Urine strip test — Understanding its limitations

Published in Biochemistry
Tuesday, 22 November 2016 01:46

Routine urinalysis is a cost-effective, non-invasive test used as an indicator of health or disease for metabolic and renal disorders, infection, drug abuse, pregnancy, and nutrition. Urine chemistry can be completed in a number of different ways, ranging from manual reading of a visual urine test strip to the use of semi-automated analyzers to loading the sample on a fully automated urine chemistry analyzer. There is one thing that all methods have in common: a urine chemistry reagent strip.

While urinalysis remains a routinely ordered laboratory test, today most of the emphasis focuses on automating urine microscopy to reduce manual, subjective microscopic work. Urine chemistry analysis is viewed by many as a screening tool that can help aid in the diagnosis of some common conditions such as urinary tract infections (UTIs), kidney or liver diseases, or diabetes, among others. It is important to remain focused on urine chemistry and better understand common test interferences.

Urine chemistry reagent strips comes in many different configurations, depending on their use. The most common tests include bilirubin, urobilinogen, glucose, ketones, protein, blood, nitrite, leukocyte esterase, and pH. In addition, some manufacturers include urine chemistry reagent pads for specific gravity, ascorbic acid, microalbumin, creatinine, and color. While urine chemistry testing is common, it is important to understand the test and its limitations to ensure accuracy of the test and recognize the factors that can cause incorrect results. Manufacturers have improved urine chemistry analysis by including additional tests to easily identify common interferences.

Bilirubin

Bilirubin (BIL) is a waste product of red blood cell (RBC) destruction. The primary source of bilirubin is the daily release of hemoglobin from the breakdown of RBCs in the reticuloendothelial system. In addition, RBC breakdown can occur in the bone marrow or other heme-containing proteins. The liver normally breaks down most of the bilirubin.

Healthy individuals exhibit a “negative” reading; very small amounts (0.02 mg/dL) can be found in urine but are undetected by routine testing techniques. The presence of bilirubin can indicate liver dysfunction such as jaundice, hemolytic disease, or obstruction of the bile duct or biliary system. A high amount of bilirubin, especially, affects the brain of newborns.

False positives can be caused by drugs that color the urine red, such as phenazopyridine, or large quantities of chlorpromazine metabolites. False negatives can be caused by the presence of ascorbic acid, increased nitrite concentrations, or improper sample storage.

Urobilinogen

Urobilinogen (URO) is a breakdown product of bilirubin. When high concentrations form in the body, the liver may not be able to break down all of the bilirubin present. Urobilinogen is produced in the intestines as bacteria metabolizes bilirubin. Small amounts (≤1 mg/dL or ≈1 Ehrlich unit) may be found in normal urine. However, the presence of urobilinogen is found with liver dysfunction, excessive destruction of RBC (hemolytic anemia, pernicious anemia and malaria), hepatitis, portal cirrhosis, and congestive heart failure.

Interferences for urobilinogen include formalin, high concentrations of nitrites, and drugs or substances that color the urine. If samples don’t equilibrate to room temperature before testing, that can produce an incorrect result.

Ketones

Ketones (KET) are normally not found in urine, but can be present when the body breaks down fat for energy. The body normally obtains energy from carbohydrates. If the carbohydrate supply is reduced, not absorbed properly, or not broken down metabolically, the body will use fat for energy. Ketones are associated with uncontrolled diabetes, vomiting, starvation, fasting, frequent strenuous exercise, and when the body uses fat instead of glucose for energy, which often occurs in people on a high-protein diet.

Agents containing free sulfhydryl groups can cause interference with ketone detection. Highly pigmented urine can result in false positive results, and improper sample or test strip storage may provide false negative results.

Glucose

Glucose (GLU) supplies the body with energy. In healthy individuals, glucose is reabsorbed by the kidney tubules and not present in the urine. However, if the concentration of blood glucose becomes too high (160-180 mg/dl), then the tubules can no longer reabsorb glucose and it will pass into the urine. This presence of glucose in the urine is called glycosuria. It is often associated with endocrine disorders such as diabetes, kidney impairment, central nervous system damage, and pancreatic disease. Other conditions associated with glycosuria include burns, infections, and fractures. Glycosuria is also associated with pregnancy.

High concentrations of ketones, decreased urine sample temperature, and increased specific gravity affect the sensitivity of the glucose pad. Increased ascorbic acid can also pose an interference. Bacterial glycolysis can occur with improper storage and can provide a false negative result.

Protein

The presence of protein (PRO) in the urine, otherwise known as proteinuria, is often the first indicator of kidney disease. It can also be indicative of other diseases such as nephrotic syndrome, glomerulonephritis, multiple myeloma, and pre-eclampsia. Exposure to cold, strenuous exercise, high fever, and dehydration can also cause the presence of protein in the urine.

The protein pad is most sensitive to albumin as opposed to other proteins. False positive results can be found with extremely alkaline samples. In addition to protein urine chemistry pads, there are also urine chemistry strips that test for microalbumin and creatinine for further assessment.

Blood

Blood (BLD) is not normally present in the urine and may not be visually present. The abnormal presence of RBCs in the urine is called hematuria, and the presence of hemoglobin in the urine is called hemoglobinuria. Blood in the urine is associated with kidney or urinary tract diseases, severe burns, infections, trauma, exposure to toxic chemicals or drugs, pyelonephritis, glomerulonephritis, renal or genital disorders, tumors, transfusion reactions, intravascular hemolysis, and hemolytic anemia. Strenuous exercise and menstruation can also cause the presence of blood in the urine. A positive result should be followed up with a microscopic correlation to assess for the present of RBCs and casts.

Urine specimens must be well mixed to ensure that RBCs have not settled out. Ascorbic acid should be considered an interferent when RBCs are present during a microscopic exam but the blood urine chemistry test is negative.

Nitrites

Nitrates (NIT) are consumed in the diet as green vegetables and are normally excreted without nitrite formation. The presence of bacteria in the urinary tract (e.g., bladder, kidney, etc.), can lead to the production of nitrites. Nitrite and leukocyte esterase screening help identify the presence of an infection. This screen should not replace further microscopic examination for bacteria or a culture to identify and quantify the bacteria present. It is used to quickly identify nitrate-reducing bacteria at a low cost.

Proper nitrite screening should be performed on a urine sample collected in the morning or after it has been retained in the bladder for at least four hours. High concentrations of ascorbic acid and improper storage can provide false results.

Leukocytes

Normal urine may contain a small number of white blood cells (WBCs) or leukocytes (LEUs). An increase in the presence of leukocyte esterase, an enzyme found in leukocytes, indicates inflammation in the urinary system. A WBC increase can be present with or without bacteriuria. If leukocytes are present without bacteria, there is usually a kidney or urinary tract infection (UTI) involving trichomonas, yeast, chlamydia, mycoplasmas, viruses, or tuberculosis. A positive nitrite and leukocyte esterase is a good indication for the performance of further microscopic examination.

High glucose, protein, and specific gravity can interfere with the leukocyte-esterase reaction, causing inaccurate results. In addition, specific antibiotics, drugs, and food (beets) can affect the chemical reaction.

pH

The kidneys play a major role in maintaining proper pH balance. Urine pH can affect the stability of formed particles in the body. Acidic urine (i.e., 4.5-6.9) is associated with, but not limited to, high-protein diets or the ingestion of cranberries, starvation, severe diarrhea, chronic lung disease, and UTIs with acid-producing bacteria (Escherichia coli) as well as certain medications. Alkaline urine (i.e., 7.0-7.9) is associated with, but not limited to, vegetarian or low-carbohydrate diets, vomiting, hyperventilation, UTIs with urease-producing bacteria, and certain medications. pHs that are below 4.5 should be suspected of adulteration, and pHs that are above 8 are often tied to improperly stored urine specimens.

Specific gravity

Specific gravity (SG) is a measure of the density of a urine. The more particles (i.e., salts, glucose, protein, etc.) in a urine, the higher the specific gravity. High specific gravity is caused by dehydration, diarrhea, heart failure, and glucose in the urine (i.e., diabetes). Low specific gravity is caused by kidney failure, diabetes insipidus, renal tubular necrosis, and the intake of too much fluids.

Urine test strips used for visual analysis often have a pH reagent pad. A limitation of the reagent pad is that it only measures the ionic solutions and can be susceptible to pH readings. Fully automated urine chemistry analyzers often use an onboard refractometer to obtain a specific gravity reading. A refractometer can be affected by particle size, temperature, and concentration of the solution as well as light wavelength. Some manufacturers have a specific gravity correction factor for high protein and glucose concentrations.

Ascorbic acid

Ascorbic acid, otherwise known as vitamin C, can be found in various foods and supplements. It is also a common interferent with urine chemistry reagent pads. When a urine sample has high levels of ascorbic acid, the reagent pads for blood, glucose, nitrite, and bilirubin may not react properly. This especially interferes with blood measurements at low levels. Clinicians should consider asking whether the patient is taking vitamin C when collecting a urine sample. We see more people taking vitamin C or vitamin C-like substances during the winter months or when traveling by plane, in an effort to boost their immune system.

Not all strip manufacturers have an ascorbic acid detection pad, as ascorbic acid is not commonly reported out. When the sample tests positive for ascorbic acid, the laboratorian may append a note with the results identifying potential interferences to the physician.

Color

Normal urine ranges from yellow/amber in color to clear or transparent and has a characteristic odor. A change in color, clarity, or odor is not necessarily a sign that something is incorrect. Urine changes color based on the body’s chemistry, food, medication intake, and state of hydration. Below is a list of colors, other than shades of yellow, found during urinalysis testing, along with their associated causes:

  • Orange: dehydration; certain medications; liver or bile duct issues
  • Blue/green: dyes in food or for kidney and bladder tests; medications such as amitriptyline, indomethacin (Indocin) and propofol (Diprivan); familial benign hypercalcemia, also known as blue diaper syndrome; UTIs caused by pseudomonas bacteria
  • Red/pink: UTIs; enlarged prostate; tumors; kidney cysts; long-distance running; kidney or bladder stones; the use of medications such as rifampin (Rifadin, Rimactane) or phenazopyridine (Pyridium); the use of some laxatives; the use of chemotherapy drugs. In addition, eating beets, blackberries, or rhubarb may cause the urine to turn red or pink
  • Brown: liver and kidney disorders; UTIs; extreme exercise; ingesting large amounts of certain foods (e.g., fava beans, rhubarb, or aloe); medications such as the antimalarial drugs chloroquine and primaquine, antibiotics metronidazole (Flagyl) and nitrofurantoin
  • Cloud/murky: urinary tract infection (UTI)

Urine color can interfere with some of the aforementioned tests during the color reaction process that takes place on the pad. For this reason, some manufacturers have a “blank” or color compensation pad on the dipstick. This color compensation pad will identify the color of the urine, and the analyzer will “subtract out” the color from other readings to provide a more accurate result.

The lab’s perspective

As noted above, specimen storage is a concern for a number of tests. Most manufacturers require testing within one to two hours of collection. If this is not feasible, samples are often refrigerated or stored in a preservative tube for testing at a later date. It’s important to note that few manufacturers have validated the use of preservative tubes for analysis on their urine analyzers, so lab leaders should assess their needs before purchasing a system.

In summary, urinalysis remains an informative laboratory test. It is important to understand what is being tested and what can interfere with the test, since certain medications and vitamins interfere with urinalysis testing. For example, during the winter months, more and more people are taking vitamin C in an effort to “starve a cold,” and we see ascorbic acid as an interference in bilirubin, glucose, blood, and nitrite testing. It is also important to understand the patient’s diet and exercise level, since they can impact results as well. Laboratorians should become very familiar with the manufacturer’s instructions for use to know what the limitations of the analyte are in order to ensure accurate reporting.

Abnormal MCH effects to HbA1c level

Published in Biochemistry
Sunday, 23 October 2016 14:51

Abstract

Background: Several hematological alterations are associated with altered hemoglobin A1c (Hb A1c). However, there have been no reports of their influence on the rates of exceeding standard Hb A1c thresholds by patients for whom Hb A1c determination is requested in clinical practice.

Methods: The initial data set included the first profiles (complete blood counts, Hb A1c, fasting glucose, and renal and hepatic parameters) of all adult patients for whom such a profile was requested between 2008 and 2013 inclusive. After appropriate exclusions, 21844 patients remained in the study. Linear and logistic regression models were adjusted for demographic, hematological, and biochemical variables excluded from the predictors.

Results: Mean corpuscular hemoglobin (MCH) and mean corpuscular volume (MCV) correlated negatively with Hb A1c. Fasting glucose, MCH, and age emerged as predictors of Hb A1c in a stepwise regression that discarded sex, hemoglobin, MCV, mean corpuscular hemoglobin concentration (MCHC), serum creatinine, and liver disease. Mean Hb A1c in MCH interdecile intervals fell from 6.8% (51 mmol/mol) in the lowest (≤27.5 pg) to 6.0% (43 mmol/mol) in the highest (>32.5 pg), with similar results for MCV. After adjustment for fasting glucose and other correlates of Hb A1c, a 1 pg increase in MCH reduced the odds of Hb A1c–defined dysglycemia, diabetes and poor glycemia control by 10%–14%.

Conclusions: For at least 25% of patients, low or high MCH or MCV levels are associated with increased risk of an erroneous Hb A1c–based identification of glycemia status. Although causality has not been demonstrated, these parameters should be taken into account in interpreting Hb A1c levels in clinical practice.

Preanalytical Errors in Clinical Chemistry Laboratory

Published in Biochemistry
Friday, 21 October 2016 22:57
Abstract: There are many factors that contribute to accurate test results in the chemistry laboratory. These factors can be broken down into three areas: preanalytical, analytical and post analytical. Preanalytical variables account for 32-75% of laboratory errors, and encompass the time from when the test is ordered by the physician until the sample is ready for analysis.1 The focus of this article will be preanalytical variables that can occur during a venipuncture and specimen processing and how they relate to testing in the clinical chemistry laboratory.
 
Scenario: A patient has been in the cardiac intensive care unit for 3 days. For the past 2 mornings, he has had his cardiac enzymes drawn into a BD SSTT tube to monitor his condition since his heart attack. On this particular morning, his tube of blood is drawn and sent to the clinical chemistry lab for analysis. However, when the tube is processed and ready for analysis, the technologist running the chemistry analyzer notices that the specimen is very gelatinous and will need to be re-processed before the sample can be run on the analyzer. What could have happened to the quality of this specimen?
There are many variables that can contribute to the quality of a chemistry specimen. This article will investigate the variables that may have contributed to the gelatinous specimen in the case of the cardiac patient, as well as the other variables that are important to specimen quality. The focus will be on the preanalytical phase of the blood collection and sample handling, up until the time that the sample is to be run on the chemistry instrument.
Following the above BD SST™ tube from time of collection until it is ready for analysis, the preanalytical variables that can contribute to the quality of the sample are as follows:
 
Patient Identification: It is important to identify a patient properly so that blood is being collected from the correct person. Drawing blood from the wrong person, or labeling the correct patient’s sample with a different patient’s label can certainly contribute to laboratory error. Perhaps in the opening scenario, the patient in the next bed, with an extremely prolonged clotting time, was drawn and labeled as the cardiac patient.
When identifying the patient, have them provide their full name, address, identification number and/or date of birth.2 Hospital inpatients should be wearing an identification band with the above information, which the phlebotomist should confirm before the venipuncture. Blood should not be drawn from a patient without a band. A nurse, physician, relative or guardian should identify patients that are unable to speak or identify themselves.
 
Patient Preparation: Prior to collecting specimens for chemistry, certain patient variables need to be considered. For certain chemistry analytes, such as glucose and cholesterol, patients need to be fasting (absence of food and liquids) for at least 12 hours prior to venipuncture. Other analytes, such as cortisol and adrenocorticotropin, have diurnal variations, where the analyte is at its highest level in the morning, and the levels gradually decrease during the course of the day.
 
Selecting the Site: Selecting the appropriate site for venipuncture can contribute to a better quality sample. The preferred site is the median cubital vein. This vein is usually the easiest to access. Generally, there is less need to probe to find the vein, which in turn should cause less trauma during the venipuncture. This will usually be the most comfortable for the patient. If the median cubital vein cannot be used, the next choice would be the cephalic vein. The last vein to consider for venipuncture is the basilic vein. This vein is in close proximity to the median nerve and brachial artery, and extreme caution must be used so that only the basilic vein is being punctured.
 
Site Preparation: Prior to venipuncture, the site should be cleansed with alcohol. Cleansing starts at the center of the vein, and should continue outward in concentric circles. Before performing the venipuncture, the alcohol should be allowed to air dry. This will help to ensure that the specimen is not contaminated with alcohol, as this can lead to hemolysis. Hemolysis can result in the spurious elevation of such analytes as potassium, lactate dehydrogenase (LD), iron and magnesium in the chemistry lab. Allowing the alcohol to dry completely will also cause less burning and pain to the patient.
 
Tourniquet Application and Time: The tourniquet should be applied approximately three to four inches above the venipuncture site. The tourniquet should be on the arm no longer than one minute. 2 A good rule of thumb to determine the one-minute tourniquet time is to remove the tourniquet when blood starts to flow into the first tube of blood being drawn. Prolonged tourniquet time can lead to an increase in various chemistry analytes, including serum protein, potassium and lactic acid due to hemoconcentration of blood at the puncture site.
 
Proper Venipuncture Technique: During phlebotomy, avoid probing to find the vein and achieve blood flow. Excessive probing and/or “fishing” to find a vein can result in a poor quality sample, including hemolysis. As mentioned previously, hemolysis can affect several chemistry analaytes.
 
Order of Draw: Following the correct order of draw during venipuncture will help to ensure accurate test results. The BD and CLSI (Clinical and Laboratory Standards Institute, formerly NCCLS) recommended order of draw for evacuated blood collection tubes is as follows (PDF).2
An example of improper order of draw that can lead to an incorrect chemistry result is drawing an EDTA tube prior to an BD SST ™ or heparin tube for chemistry testing. The potential cross contamination of K2 or K3EDTA on the needle from the lavender top tube to the chemistry tube can lead to an elevated potassium result. This in turn can require a recollection of the sample, or possible misdiagnosis or treatment of the patient.
 
Proper Tube Mixing: All tubes with additives need to be inverted to mix the additive evenly with the blood. Plastic serum tubes and BD SST™ tubes contain clot activator and should be inverted 5 times to mix the activator with the blood and help the specimen clot completely. In the opening case study, improper mixing of the tube after venipuncture could have contributed to the gelatinous serum sample that was seen in the laboratory. Other additive tubes, such as heparin, need to be inverted 8-10 times to mix the anticoagulant with the blood and prevent clotting. Be sure that tubes are not being shaken vigorously, as this can lead to a hemolyzed sample.
 
Correct Specimen Volume: All blood collection tubes need to be filled to the correct volume.3 This will ensure the proper amount of blood for the amount of additive in the tube (blood to additive ratio). For example, if a 5 mL draw heparin tube is only filled with 3 mL of blood, the heparin concentration is erroneously high and may potentially interfere with some chemistry analytes. Expiration dates should also be checked on the evacuated tubes.4 Expired tubes should not be used, as they may have a decreased vacuum, as well as potential changes in any additives in the tubes.
 
Proper Tube Handling and Specimen Processing: Once the blood collection tubes have been drawn in the correct order, to the proper fill volume and mixed thoroughly, the next step toward accurate test results is processing the tubes properly. This section will look at serum and plasma tubes separately, as both specimen types have their own special handling requirements.
 
Serum Samples
Serum specimens, namely red top tubes and BD SST™ gel tubes, need to clot completely prior to centrifugation and processing. Blood specimens in red top tubes should clot for 45 to 60 minutes, and those in BD SST ™ tubes should be allowed to clot for 30 minutes to ensure complete clot formation.4 Blood from patients who are receiving anticoagulant therapy, such as heparin or coumadin, may take longer to clot. Tubes should be allowed to clot at room temperature, upright in a test tube rack, with the closures on the tubes. In the gelatinous sample that was presented at the beginning of this article, perhaps the blood was not clotted completely prior to centrifugation because a cardiac patient is often heparanized. Spinning the tube too soon may result in a gelatinous and/or fibrinous serum sample that will require respinning.
 
Plasma Samples
Blood specimens collected in plasma tubes, such as the plain heparinized green top tubes and the BD PST™ tubes with heparin and gel do not require clotting prior to centrifugation. This allows the tube of blood to be drawn, mixed and centrifuged immediately, resulting in a quicker turn-around-time for test results.
 
Centrifugation: The next step in sample processing is the centrifugation of the blood collection tubes. Both BD SST™ and BD PST™ tubes are centrifuged at the same speed and for the same amount of time. In a swinging bucket centrifuge (preferred type of spin for gel separation tubes), the tubes should be spun for ten minutes at a speed of 1100 to 1300 relative centrifugal force (RCF). A fifteen-minute spin at the same speed is required for spinning tubes in a fixed- angle centrifuge. Serum and plasma tubes without gel can be spun at a speed of 1000 RCF for ten minutes.4
It is important to spin gel tubes for the recommended time. The gel barrier in the tubes needs time to move and form a solid barrier between the red cells and the serum or plasma. Also, in BD PST™ tubes, the white blood cells and platelets that remain in the plasma need adequate time to spin out of the plasma. If the BD PST™ tubes are spun for less than the recommended 10 minutes, these cells and platelets may remain in the plasma and could cause interference with some chemistry analytes. It is recommended that BD SST™ tubes should not be re-centrifuged after their initial centrifugation. Re-spinning the tubes can result in elevated potassium values, as excess serum that has been in contact with the red cells will be expressed from underneath the gel barrier.
 
Special Handling of Blood Specimens: Certain chemistry analytes will require the tube of blood to be chilled after collection in order to maintain the stability of the analyte. A slurry of ice and water is recommended for chilling the tubes of blood. Examples of specimens that need to be chilled or transported on ice include adrenocorticotropic hormone (ACTH), angiotensin converting enzyme (ACE), acetone, ammonia, catecholamines, free fatty acids, lactic acid, pyruvate and renin.
Other anayltes are photo-sensitive, and need to be protected from light in order to remain stable and to ensure that the laboratory reports an accurate result. This can be done by wrapping the tube of blood in aluminum foil. The most common example of a light-sensitive analyte is bilirubin. Other chemistry analytes that need to be light-protected include beta-carotene and erythrocyte protoporphyrin.
 
Stability for Whole Blood, Serum and Plasma: A whole blood specimen that is going to be spun down should be centrifuged and the serum or plasma removed from the red blood cells within two hours after the venipuncture.5 Once the serum has been removed or separated from the red blood cells (in the case of a gel barrier tube), the sample will be stable at room temperature for eight hours, and up to 48 hours at 2-4 degrees C.5 After 48 hours, the serum specimen should be frozen at –20 degrees C in an aliquot tube.5
Paying close attention to the preanalytical variables associated with blood collection will help to ensure accurate test results in the chemistry department, as well as all areas of the clinical laboratory. As was evident from the opening case study, there are often several variables that can potentially contribute to erroneous test results. Our cardiac patient’s blood could have been drawn from the wrong patient, had improper tube handling or his blood may have not clotted long enough. Therefore, it is important to remember that a better quality sample during the preanalytical phase of blood collection will yield a better test result.
 
References
1. Bonini P, PlebaniM, Ceriotti F, et al. Errors in laboratory medicine. Clin Chem. 2002;48:691-698.
2. NCCLS – Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture; Approved Standard, Fifth Edition, H3-A5 Vol. 23 No. 32, December 2003.
3. NCCLS – Tubes and Additives for Blood Specimen Collection; Approved Standard-Fifth Edition, H1- A5 Vol. 23 No. 33, December 2003.
4. BD Evacuated Blood Collection System Package Insert 6/2004
5. NCCLS – Procedures for the Handling and Processing of Blood Specimens; Approved Standard-Third Edition, H18-A3 Vol. 24 No. 38, November 2004.

New finding: Biobank storage time affects blood test results

Published in Biochemistry
Wednesday, 28 September 2016 19:43
The amount of time a blood sample has been stored at a biobank may affect the test results as much as the blood sample provider’s age. These are the findings of a new study from Uppsala University, which was published in the scientific journal EBioMedicine. Until now, medical research has taken into account age, sex and health factors of the person providing the sample, but it turns out that storage time is just as important.

They analysed 380 different samples from 106 women between the ages of 29 and 73. To study the impact of storage time, only samples from 50-year-old women were used in order to isolate the time effect. 108 different proteins were analysed. In addition to how long a sample had been frozen, the researchers also looked at what year the sample was taken and the age of the patient when the sample was taken.

‘We suspected that we’d find an influence from storage time, but we thought it would be much less’, says Professor Ulf Gyllensten. ‘It has now been demonstrated that storage time can be a factor at least as important as the age of the individual at sampling.’

Blood from biobanks has been used in research aimed at producing new drugs and testing new treatment methods. The results of this study are important for future drug research, but it is not possible or necessary, to repeat all previous biobank analyses.


Read more: New finding: Biobank storage time affects blood test results

BRS Biochemistry, Molecular Biology, and Genetics 6th Ed.

Published in Downloads
Saturday, 17 September 2016 18:41
Description: BRS Biochemistry, Molecular Biology, and Genetics is an excellent aid for USMLE Step 1 preparation and for coursework in biochemistry, molecular biology, and genetics. Fully updated for its sixth edition, chapters are written in an outline format and include pedagogical features such as bolded key words, figures, tables, algorithms, and highlighted clinical correlates. USMLE-style questions and answers follow each chapter and a comprehensive exam appears at the end of the book.

Porphyrias

Published in Biochemistry
Sunday, 03 July 2016 21:15
Porphyrias

Porphyrias (from Greek porphura meaning purple pigment; the name is probably derived from purple discoloration of some body fluids during the attack) are a heterogeneous group of rare disorders resulting from disturbance in the heme biosynthetic pathway leading to the abnormal accumulations of red and purple pigments called as porphyrins in the body. Heme, a component of hemoglobin, is synthesized through various steps as shown in figure. Each of the steps is catalyzed by a separate enzyme; if any of these steps fails (due to hereditary or acquired cause), precursors of heme (porphyrin intermediates) accumulate in blood, get deposited in skin and other organs, and excreted in urine and feces. Depending on the site of defect, different types of porphyrias are described with varying clinical features, severity, and the nature of accumulated porphyrin.
 
Porphyria has been offered as a possible explanation for the medieval tales of vampires and werewolves; this is because of the number of similarities between the behavior of persons suffering from porphyria and the folklore (avoiding sunlight, mutilation of skin on exposure to sunlight, red teeth, psychiatric disturbance, and drinking of blood to obtain heme).
 
Porphyrias are often missed or wrongly diagnosed as many of them are not associated with definite physical findings, screening tests may yield false-negative results, diagnostic criteria are poorly defined and mild disorders produce an enzyme assay result within ‘normal’ range.
 
Heme is mainly required in bone marrow (for hemoglobin synthesis) and in liver (for cytochromes). Therefore, porphyrias are divided into erythropoietic and hepatic types, depending on the site of expression of disease. Hepatic porphyrias mainly affect the nervous system, while erythropoietic porphyrias primarily affect the skin. Porphyrias are also classified into acute and nonacute (or cutaneous) types depending on clinical presentation.
 
Inheritance of porphyrias may be autosomal dominant or recessive. Most acute porphyrias are inherited in an autosomal dominant manner (i.e. inheritance of one abnormal copy of gene). Therefore, the activity of the deficient enzyme is 50%. When the level of heme falls in the liver due to some cause, activity of ALA synthase is stimulated leading to increase in the levels of heme precursors up to the point of enzyme defect. Increased levels of heme precursors cause symptoms of acute porphyria. When the heme level returns back to normal, symptoms subside.
 
Accumulation of porphyrin precursors can occur in lead poisoning due to inhibition of enzyme aminolevulinic acid dehydratase in heme biosynthetic pathway. This can mimick acute intermittent porphyria.

Lippincott's Illustrated Reviews Biochemistry, 5th Edition by Pamela C. Champe

Published in Downloads
Monday, 02 May 2016 10:35
Description: Lippincott’s Illustrated Reviews: Biochemistry is the long-established first-and best resource for the essentials of biochemistry. Students rely on this text to help them quickly review, assimilate, and integrate large amounts of critical and complex information. For more than two decades, faculty and students have praised LIR Biochemistry’s matchless illustrations that make concepts come to life.
Advertisement

Useful Sites

  • NCBI

    National Center for Biotechnology Information
  • LTO

    Lab Tests Online® by AACC
  • ASCP

    American Society for Clinical Pathology
  • ASM

    American Society for Microbiology
  • The Medical Library®

    Project of BioScience.pk
Advertisement

Connect With Us

Contact Us

All comments and suggestions about this web site are very welcome and a valuable source of information for us. Thanks!

Tel: +(92) 302 970 8985-6

Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Website: https://www.bioscience.pk



This website is certified by Health On the Net Foundation. Click to verify. This site complies with the HONcode standard for trustworthy health information:
verify here.

Our Sponsors

InsightGadgets.comPathLabStudyTheMedicalLibrary.orgThe Physio ClubB2BPakistan.com

By using BioScience.pk you agree to our use of cookies to enhance your experience on this website.