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Lab Manual for UCSF Clinical Laboratories

Lab Manual for SFGH

Internal Resources


Item Value
Approval req'd? no
Available Stat? No
Test code OCX1, OCX2, OCX3
Performed by? Hematology
Sendout? no
Price range $
In House Availability 24 hours/ 7 days
Principle The guaiac test for occult blood depends on the oxidation of a phenolic compound, alpha guaiaconic acid, to a blue quinone structure. Hemoglobin exerts a peroxidase-like activity and facilitates oxidation by hydrogen peroxide. The test is a simplified, standardized variation of the guaiac test. When a stool specimen containing occult blood is applied to the test pad, the hemoglobin from lysed red cells comes in contact with the guaiac-impregnated paper. Application of Developer (a stabilized hydrogen peroxide solution) turns the test paper blue in 30 to 60 seconds in the presence of occult blood.
Interpretation The test is a screening procedure designed to detect bleeding due to colorectal cancer, gastrointestinal hemorrhage, or other gastrointestinal pathology. A positive result indicates that further diagnostic procedures are necessary.

As of May 2016, all ZSFG and COPC clinics switched to automated fecal immunochemical testing (FIT) using the OC-Auto SENSOR DIANA iFOB analyzer, by Polymedco, for colorectal cancer screening.
Container type stool collection card
Sample type Stool
Special instructions Ascorbic acid (Vitamin C) in excess of 250 mg/day may cause false negative results and should be discontinued two days before testing.

The manufacturer recommends that, if practical, patients should be placed on a meat-free high residue diet, starting two days before the test period, in order to reduce the number of false positive reactions and help uncover lesions that may bleed only intermittently.
Some oral medications (e.g., aspirin, indomethacin, phenylbutanzone, corticosteroids, reserpine, etc.) may cause occult bleeding. These substances should be discontinued, if possible, two days prior to testing.
Normal range Negative.
Synonyms Fecal Occult Blood;Guaiac;Stool Occult Blood;
Additional information Note: This method is designed for fecal occult blood only.
References 1. Beckman Coulter Hemoccult, Product Instructions. August 2003.
CPT coding 82270
Last Updated 8/7/2017 10:53 AM
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