University:
Saint Louis University
Course:
PATH 0100 | Introduction to Pathology
Academic year:

2024
Views:

197

Pages:

2
Author:

brian 11kizz

Occult Blood Examination Objective: to detect small bleeding that cannot be detected macroscopically or microscopically. There are 3 methods: 1.With benzidine base 2.With benzidine dihydrochloride 3.With guajac Occult Blood Test with Benzidine Base How it works: 1. Make a stool emulsion with 10 ml of water or 0.9% NaCl-heat until boiling 2. Filter the hot emulsion, leave the filtrate until it cools again 3. Put a knife's amount of Benzidine base into another test tube 4. Add 3 ml of glacial acetic acid - shake until the benzidine dissolves leaving some crystals. 5. Add 2 ml of fecal emulsion filtrate - mix 6. Add 1 ml of 3% H2O2 solution - mix 7. Results are read within 5 minutes (don't take longer) Results are assessed by: 1. Negative (-): no color change or faint green color 2. Positive + : green 3. Positive 2+ : blue mixed with green 4. Positive 3+ : blue 5. Positive 4+ : dark blue Note: to get meaningful results, the examination should be carried out more than once. Occult Blood Examination with Benzidine Dihydrochloride Purpose: 1.As a substitute for benzidine base 2.So that the test is sensitive and does not produce false positives Method: the same as using benzidine base. Attention: be careful when using benzidine!!! Occult Blood Examination with Guajac Ways of working: 1. Make 5 ml of fecal emulsion in a test tube and add 1 ml of glacial acetic acid - mix 2. Put a knife of guajac powder and 2 ml of 95% alcohol in another test tube -c mix 3. Carefully pour the contents of the second tube into the tube containing the fecal emulsion - both types of mixture remain as separate layers 4. Positive result: blue color appears at the boundary of the two layers. The degree of positivity is judged by that color.