- Life processes, interactions, and adaptations
- The movement of materials and energy through living communities
- The successional development of ecosystems
- The abundance and distribution of organisms and biodiversity in the context of the environment.
- Brown: Normal
- Black: Bleeding in upper gastrointestinal tract (proximal to cecum), Drugs (iron salts, bismuth salts, charcoal)
- Red: Bleeeding in large intestine, undigested tomatoes or beets
- Clay-colored (gray-white): Biliary obstruction
- Silvery: Carcinoma of ampulla of Vater
- Watery: Certain strains of Escherichia coli, Rotavirus enteritis, cryptosporidiosis
- Rice water: Cholera
- Unformed with blood and mucus: Amebiasis, inflammatory bowel disease
- Unformed with blood, mucus, and pus: Bacillary dysentery
- Unformed, frothy, foul smelling, which float on water: Steatorrhea.
- Sedimentation techniques: Ova and cysts settle at the bottom. However, excessive fecal debris may make the detection of parasites difficult. Example: Formolethyl acetate sedimentation procedure.
- Floatation techniques: Ova and cysts float on surface. However, some ova and cysts do not float at the top in this procedure. Examples: Saturated salt floatation technique and zinc sulphate concentration technique.
- Occult blood
- Excess fat excretion (malabsorption)
- Reducing sugars
- Fecal osmotic gap
- Fecal pH
- Intestinal diseases: hookworms, amebiasis, typhoid fever, ulcerative colitis, intussusception, adenoma, cancer of colon or rectum.
- Gastric and esophageal diseases: peptic ulcer, gastritis, esophageal varices, hiatus hernia.
- Systemic disorders: bleeding diathesis, uremia.
- Long distance runners.
- Ingestion of peroxidase-containing foods like red meat, fish, poultry, turnips, horseradish, cauliflower, spinach, or cucumber. Diet should be free from peroxidase-containing foods for at least 3 days prior to testing.
- Drugs like aspirin and other anti-inflammatory drugs, which increase blood loss from gastrointestinal tract in normal persons.
- Foods containing large amounts of vitamin C.
- Conversion of all hemoglobin to acid hematin (which has no peroxidase-like activity) during passage through the gastrointestinal tract.
- Deficiency of pancreatic lipase (insufficient lipolysis): chronic pancreatitis, cystic fibrosis.
- Deficiency of bile salts (insufficient emulsification of fat): biliary obstruction, severe liver disease, bile salt deconjugation due to bacterial overgrowth in the small intestine.
- Diseases of small intestine: tropical sprue, celiac disease, Whipple’s disease.
- Microscopic stool examination after staining for fat: A random specimen of stool is collected after putting the patient on a diet of >80 gm fat per day. Stool sample is stained with a fat stain (oil red O, Sudan III, or Sudan IV) and observed under the microscope for fat globules (Figure 845.2). Presence of ≥60 fat droplets/HPF indicates steatorrhea. Ingestion of mineral or castor oil and use of rectal suppositories can cause problems in interpretation.
- Quantitative estimation of fecal fat: The definitive test for diagnosis of fat malabsorption is quantitation of fecal fat. Patient should be on a diet of 70-100 gm of fat per day for 6 days before the test. Feces are collected over 72 hours and stored in a refrigerator during the collection period. Specimen should not be contaminated with urine. Fat quantitation can be done by gravimetric or titrimetric method. In gravimetric method, an accurately weighed sample of feces is emulsified, acidified, and fat is extracted in a solvent; after evaporation of solvent, fat is weighed as a pure compound. Titrimetric analysis is the most widely used method. An accurately weighed stool sample is treated with alcoholic potassium hydroxide to convert fat into soaps. Soaps are then converted to fatty acids by the addition of hydrochloric acid. Fatty acids are extracted in a solvent and the solvent is evaporated. The solution of fat made in neutral alcohol is then titrated against sodium hydroxide. Fatty acids comprise about 80% of fecal fat. Values >7 grams/day are usually abnormal. Values >14 grams/day are specific for diseases causing fat malabsorption.
(Plasma sodium × Urine creatinine)
- Causes of increased specific gravity:
a. Reduced renal perfusion (with preservation of concentrating ability of tubules),
e. Urinary tract obstruction.
- Causes of reduced specific gravity:
a. Diabetes insipidus
b. Chronic renal failure
c. Impaired concentrating ability due to diseases of tubules.