- A clean and dry glass slide is divided into two sections with a glass marking pencil. The sections are labeled as anti-A and anti-B to identify the antisera (see Figure 786.2).
- Place one drop of anti-A serum and one drop of anti-B serum in the center of the corresponding section of the slide. Antiserum must be taken first to ensure that no reagents are missed.
- Add one drop of blood sample to be tested to each drop of antiserum.
- Mix antiserum and blood by using a separate stick or a separate corner of a slide for each section over an area about 1 inch in diameter.
- By tilting the slide backwards and forwards, examine for agglutination after exactly two minutes.
Positive (+): Little clumps of red cells are seen floating in a clear liquid.
Negative (–): Red cells are floating homogeneously in a uniform suspension.
- Interpretation: Interpret the result as shown in the Table 786.1 and Figure 786.2.
Separate tubes of auto-control, positive control, and negative control should always be setup along with the test sample tube. Auto-control tube consists of mixture of patient’s red cells and patient’s own serum. This is required to rule out false-positive result due to auto antibodies in patient’s serum causing auto agglutination of patient’s own red cells. Auto-control test is particularly essential when ABO grouping is being done only by forward method and blood group is typed as AB. If there are auto antibodies in recipient’s serum, ABO grouping, Rh typing, antibody screening, and cross matching all will show positive result.
If forward grouping, reverse grouping, and autocontrol tests are all positive, then these results are probably indicative of a cold-reactive autoantibody. Before performing forward typing, red cells should be washed with normal saline to elute the antibody. Before performing reverse grouping, autoantibody should be adsorbed by washed cells till autocontrol is negative.
- Scan the slide in a methodical grid pattern, in order not to cover the same area twice. Counts can be completed quickly under 400×magnification, but if you are also evaluating morphology, 1000×magnification should be used.
- Count a minimum of 100 WBCs.
- Manual or microscopic method
- Automated method
Hemocytometer with cover glass, compound microscope.
HgCl2 0.05 gm
NaSO4 2.5 gm
NaCl 0.5 gm
Distilled water 100 ml
- Wipe finger with cotton soaked with alcohol, with a sterile lancet do small prick on the finger tip. Use pipette. Aspirate blood to 0.5.
- Aspirate diluting Hayem’s solution to the 101 mark. It will give 1:200 dilution of the blood.
- Hold the pipette horizontally and role it with both hands between finger and thumb.
- Place the counting chamber, absolutely free from dust and grease, on the table and lay the cover glass in place over the ruled area.
- Discard the first two or three drops from the pipette. Charge the counting chamber by holding the pipette in an inclined position. Allow 3 minutes for the cells to settle.
- Locate the central square, which is divided into 25 medium sized squares. Each of the medium sized squares is further divided into 16 smallest squares.
- Count the erythrocytes in medium sized squares (80 smallest squares) using high power objective.
- In order to avoid confusion in counting, count all cells wihich touch the upper and left outer double line of the group of 16 squares as if they were inside the square. Neglect all those cells, which touch the lower and right inner line.
= 1/5 sq mm
= 1/5 sqmm x 1/10 mm
= 1/50 cu mm
(1) Increased in numbers of RBC called polycythemia it is due to
• Bone marrow failure
• Erythropoietin deficiency (2ndry to kidney disease)
• Hemolysis (RBC destruction) from transfusion reaction
• Multiple myloma
• Nutritional deficiencies of (Iron, Copper, Folate, Vit B12, B6)
• Newborns: 4.8-7.2 millions
• Children: 3.8-5.5 millions
• Adult ( male): 4.6-6.0 millions
• Adult (Females): 4.2-5.0 millions
• Pregnancy: slightly lower than normal
- Brown, B.A., Haemotology, Principles and Procedures, Lea & Febiger, U.S.A., 1976.
- Hoffbrand, A. V. and Pettit, 1. E., Essential Haemotology, Blackwell Scientific Publication, U.S.A., 1980.
- Kassirsky, I. and Alexeev, G., Clinical Haemotology, Mir Publishers, U.S.S.R., 1972.
- Widmann, F.K., Clinical interpretation of Laboratory tests, F.A. Davis Company, U.S.A., 1985.
- Kirk, C.J.C. et al, Basic Medical Laboratory Technology, Pitman Book Ltd., U.K. 1982.
- Green, J.H., An Introduction to human Physiology, Oxford University Press, U.K., 1980.
Anticoagulated whole blood is centrifuged in a capillary tube of uniform bore to pack the red cells. Centrifugation is done in a special microhematocrit centrifuge till packing of red cells is as complete as possible. The reading (length of packed red cells and total length of the column) is taken using a microhematocrit reader, a ruler, or arithmetic graph paper.
- Microhematocrit centrifuge: It should provide relative centrifugal force of 12000 g for 5 minutes.
- Capillary hematocrit tubes: These are disposable glass tubes 75 mm in length and 1 mm in internal diameter. They are of two types: plain (containing no anticoagulant) and heparinised (coated with a dried film of 2 units of heparin). For plain tubes, anticoagulated venous blood is needed. Heparinised tubes are used for blood obtained from skin puncture.
- Tube sealant like plastic sealant or modeling clay; if not available, a spirit lamp for heat sealing.
- Microhematocrit reader; if not available, a ruler or arithmetic graph paper.
Venous blood collected in EDTA (dipotassium salt) for plain tubes or blood from skin puncture collected directly in heparinised tubes. Venous blood should be collected with minimal stasis to avoid hemoconcentration and false rise in PCV.
- Fill the capillary tube by applying its tip to the blood (either from skin puncture or anticoagulated venous blood, depending on the type of tube used). About 2/3rds to 3/4ths length of the capillary tube should be filled with blood.
- Seal the other end of the capillary tube (which was not in contact with blood) with a plastic sealant. If it is not available, heatseal the tube using a spirit lamp.
- The filled tubes are placed in the radial grooves of the centrifuge with the sealed ends toward the outer rim gasket. Counterbalance by placing the tubes in the grooves opposite to each other.
- Centrifuge at relative centrifu-gal force 12000 g for 5 minutes to completely pack the red cells.
- Immediately remove the tubes from the centrifuge and stand them upright. The tube will show three layers from top to bottom: column of plasma, thin layer of buffy coat, and column of red cells.
- With the microhematocrit reader, hematocrit is directly read from the scale. If hematocrit reader is not available, the tube is held against a ruler and the hematocrit is obtained by the following formula:
Length of total column in mm
- Prolonged application of tourniquet during venepuncture causes hemoconcentration and rise in hematocrit.
- Excess squeezing of the finger during skin puncture dilutes the sample with tissue fluid and lowers the hematocrit.
- Correct proportion of blood with anticoagulant should be used. Excess EDTA causes shrinkage of red cells and falsely lowers the hematocrit.
- Inadequate mixing of blood with anticoagulant, and inadequate mixing of blood before testing can cause false results.
- Low hematocrit can result if there are clots in the sample.
- Centrifugation at lower speed and for less time falsely increases PCV.
- A small amount of plasma is trapped in the lower part of the red cell column which is usually insignificant. Increased amount of plasma is trapped in microcytosis, macrocytosis, spherocytosis, and sickle cell anemia, which cause an artifactual rise in hematocrit. Larger volume of plasma is trapped in Wintrobe tube than in capillary tube.
- As PCV requires whole blood sample, it is affected by plasma volume (e.g. PCV is higher in dehydration, and lower in fluid overload).
- Expression of PCV: Occasionally, PCV is expressed as a percentage. In SI units, PCV is expressed as a volume fraction. Conversion factor from conventional to SI units is 0.1 and from SI to conventional units is 100.
- Rules of 3 and 9: These rules of thumb are commonly used to check the accuracy of results and are applicable only if red cells are of normal size and shape.
• Hemoglobin (gm/dl) × 3 = PCV
• Red cell count (million/cmm) × 9 = PCV
- Automated hematocrit: In automated hematology analyzers, hematocrit is obtained by multiplying red cell count (in millions/cmm) by mean cell volume (in femtoliters).
- Adult males: 40-50%
- Adult females (nonpregnant): 38 45%
- Adult females (pregnant): 36-42%
- Children 6 to 12 years: 37-46%
- Children 6 months to 6 years: 36 42%
- Infants 2 to 6 months: 32-42%
- Newborns: 44-60%
- Packed cell volume: < 20% or > 60%
- Wintrobe tube: This tube is about 110 mm in length and has 100 markings, each at the interval of 1 mm. Internal diameter is 3 mm. It can hold about 3 ml of blood.
- Pasteur pipette with a rubber bulb and a sufficient length of capillary to reach the bottom of the Wintrobe tube.
- Centrifuge with a speed of 2300 g.
- Mix the anticoagulated blood sample thoroughly.
- Draw the blood sample in a Pasteur pipette and introduce the pipette up to the bottom of the Wintrobe tube. Fill the tube from the bottom exactly up to the 100 mark. During filling, tip of the pipette is raised, but should remain under the rising meniscus to avoid foaming.
- Centrifuge the sample at 2300 g for 30 min (To counterbalance a second Wintrobe tube filled with blood from another patient or water should be placed in the centrifuge).
- Take the reading of the length of the column of red cells.
After centrifugation of anticoagulated whole blood, three zones can be distinguished in the Wintrobe tube from above downwards-plasma, buffy coat layer (a small greyish layer of white cells and platelets, about 1 mm thick), and packed red cells. Normal plasma is straw-colored. It is colorless in iron deficiency anemia, pink in the presence of hemolysis or hemoglobinemia, and yellow if serum bilirubin is raised (jaundice). In hypertriglyceridemia, plasma appears milky. Increased thickness of buffy coat layer occur if white cells or platelets are increased in number (e.g. in leukocytosis, thrombocytosis, or leukemia). Smears can be made from the buffy coat layer for demonstration of lupus erythematosus (LE) cells, malaria parasites, or immature cells.
WHAT IS PACKED CELL VOLUME (PCV) OR HEMATOCRIT? USES AND METHODS FOR ESTIMATION OF PACKED CELL VOLUME (PCV)Monday, 17 July 2017 11:02
- Detection of presence or absence of anemia or polycythemia
- Estimation of red cell indices (mean cell volume and mean corpuscular hemoglobin concentration)
- Checking accuracy of hemoglobin value (Hemoglobin in grams/dl × 3 = PCV).
This method is also more accurate as plasma trapping in red cell column is less.
This method is rapid and simple. However, no stable standard solution is available, color of oxyhemoglobin solution rapidly fades, and hemoglobin derivatives other than oxyhemoglobin are not measured.
Objective: To test organism's ability to tolerate various osmotic concentrations.
1. Use a sterile loop or needle to inoculate broth tubes with different salt concentrations.
2. Incubate at the optimum temperature for 48-96 hours.
Positive = growth; Negative = no growth
Objective: To test the organism's susceptibility to antibiotic penicillin.
Test Procedure and Interpretation: See the Optochin Disc Test.
Discovery of Penicillin
The discovery of penicillin's antibiotic powers is attributed to Alexander Fleming. The story goes that he returned to his laboratory one day in September 1928 to find a Petri dish containing Staphylococcus bacteria with its lid removed.
The dish had become contaminated by blue-green mold. He noted that there was a clear ring surrounding the mold where the bacteria had been inhibited from growing.
This discovery of the mold - Penicillium notatum - and his recognition of its special powers set the wheels in motion to create one of the most used drugs in medical history.
In March 1942, Anne Miller became the first civilian to be treated successfully with penicillin having almost died from a huge infection following a miscarriage.
Although Fleming often gets the accolade for having invented the first antibiotic, there was a lot of work to do before penicillin could become as commonly used and useful as it is today.
The bulk of the work was eventually carried out by scientists who had a much better-stocked laboratory and a deeper understanding of chemistry than Fleming. Dr. Howard Florey, Dr. Norman Heatley, and Dr. Ernst Chain carried out the first in-depth and focused studies.
Interestingly, and with impressive foresight, Fleming's Nobel Prize acceptance speech warned that the overuse of penicillin might, one day, lead to bacterial resistance.