Angeles University FoundationAngeles City, Pampanga

College of Allied Medical ProfessionsDepartment of Medical Technology

Routine Stool Examination: Chemical Phase

Submitted by:Group3 BSMT-3C

Bautista, Joseph Ryan C.Gamboa, Lois Danielle L.Gundran, Angelika Joy

Introduction

Gross or macroscopic examination of stool may not always reveal the presence of blood, which is why chemical examination for occult blood is employed. Occult blood, generally, is not present. If there is occult blood detected in the stool specimen, it indicates either infection or some disorder of the digestive system.

Other chemical tests for fecal specimen include detection of reducing substances and determination of pH. Strongly acidic stool (pH below 5.5) indicates an excess of carbohydrates in the diet. It is non–pathologic. But, if fermentation is present, it may be due to lactose intolerance. Then, it is pathologic. Strongly alkaline stool (pH above 7.5) indicates an excess of protein in the diet. It is non–pathologic. Reducing substances are generally found in stools of infants suffering from diarrhea.

Flowchart/Brief Summary of the Procedure

Guaiac Test

It is performed using a slide that contains paper squares coated with guaiac, a chemical derived from resin of a tree of the genus Guaiacum. A small portion of fecal/stool specimen is applied to the paper squares in the special slide. Then, a developer solution containing hydrogen peroxide is added to the paper. If blood is present in the specimen, the iron (Fe) in the hemoglobin catalyzes the reaction between the guaiac and the hydrogen peroxide, forming a blue color. Fecal occult blood determination is based on the detection of the pseudoperoxidase activity of hemoglobin.

Results and Interpretation

Results Obtained: Negative for Occult Blood Test

Manner of Reportingo Trace – very faint blueo + - faint blueo ++ - distinct blueo +++ - dark blueo ++++ - prussian blue

Answer to Research Questions1. State the principle of fecal occult blood determination.

o Fecal occult blood determination is based on the pseudoperoxidase activity of hemoglobin in which liberates oxygen from the reaction of stool and hydrogen peroxide to oxidize the guaiac reagent.

2. What are the different indicators that are used in the detection of fecal occult blood?o Guaiac resin - When the hydrogen peroxide is dripped on to the guaiac paper, it

oxidizes the alpha-guaiaconic acid to a blue colored quinone.o Benzidine - the suspected fluid is treated with glacial acetic acid and ether, and the

latter is then decanted and treated with hydrogen peroxide and a solution of benzidine in acetic acid; the presence of blood is indicated by a bluish colour turning to purple.

o Imipramine hydrochloride (IPH) and desipramine hydrochloride (DPH)- proposed as new reagents for detection of fecal occult blood. The usefulness of IPH and DPH in occult blood detection has been examined and compared with benzidine and stanoccult methods. The results show that the proposed reagents are selective and sensitive and gives reproducible results. The proposed methodology is much less

Negative for Occult Blood Positive for Occult Blood

subject to vegetable peroxidase, iron and vitamin C interference and can be performed on patients who are on a normal diet.

Updates/Related Journal

Digestive Diseases and SciencesOctober 1997, Volume 42, Issue 10, pp 2064-2071“Performance Characteristics and Comparison of Two Immunochemical and Two Guaiac Fecal Occult Blood Screening Tests for Colorectal Neoplasia”

A new immunochemical test for stool Hb, FlexSureOBT, was compared with the immunochemical HemeSelect and guaiac Hemoccult II and Hemoccult SENSA tests. Blinded development of test cards smeared with stools having added human blood showed better analytical sensitivity of FlexSure OBT (0.2 ml blood/100g feces), than Hemoccult SENSA (≥0.5 ml) or Hemoccult II (≥1.0 ml). All four stool tests were prepared by 403 subjects having endoscopic examinations. The guaiac tests and FlexSure OBT were easy to prepare and develop. The positivity rate of Hemoccult SENSA was 8.7%, Hemoccult II 6%, FlexSure OBT 4.2%, and HemeSelect 3.4%. In this population, guaiac tests were as sensitive as immunochemical tests for clinically significant colorectal neoplasia, but with significantly lower predictive positive values. A combination of a sensitive guaiac test (Hemoccult SENSA) and a specific confirmatory test for human Hb (FlexSure OBT) provided high specificity, comparable to HemeSelect.

References:o B. Estridge, Basic Clinical Laboratory Techniques, 2011, pp. 680-681o S. Strasinger, Urinalysis and Body Fluids, 5th Edition, pp. 245-251o http://www.aarogya.com/conditions-and-diseases/diagnostic-tests/physical-a-chemical-

examination.html