Procedure

GASTRIC OCCULT BLOOD AND PH BY GASTROCCULT

Prepared by	Date Adopted	Supersedes Procedure
		New Procedure

Review Date

Revision Date

Signature

Distributed to	No. of Copies	Distributed to	No. of Copies
Pathology Department	1
Nursing Department	10

PRECAUTION: WHILE PERFORMING THIS PROCEDURE, THE FOLLOWING

SAFETY MEASURES MUST BE TAKEN: GLOVES MUST BE WORN; SMOKING, EATING, DRINKING, APPLICATION OF COSMETICS, AND MANIPULATION OF CONTACT LENSES ARE PROHIBITED IN ALL TECHNICAL WORK AREAS. REFER TO THE UNIVERSAL PRECAUTIONS POLICIES.

CLIA Complexity: Waived-Definitive

I. Principle

Gastroccult is a rapid screening test designed for detecting the presence of occult blood and determining pH of gastric aspirate or vomitus. The Gastroccult slide includes both a specially buffered guaiac test for occult blood and a pH test based on the principle that certain dyes change color with changes in hydrogen ion concentration. This test is based on the oxidation of a phenolic compound, alpha guaiaconic acid, to a blue quinone structure. Hemoglobin exerts a peroxidase-like activity and facilitates the oxidation of this phenolic compound by a buffered, stabilized hydrogen peroxide solution (active component of the developer).

The Gastroccult test is designed for use as a preliminary screening aid in the diagnosis and management of various gastric conditions and is not intended to replace other diagnostic procedures. The identification of occult blood can be useful in the early detection of gastric trauma or deteriorating gastric condition, while pH may be of use in evaluating antacid therapy.

II. Specimen

Either gastric aspirate obtained by nasogastric intubation or vomitus is an appropriate sample for use with the Gastroccult test. Prior to collecting the patient’s sample, the patient’s identity must be verified by looking at the arm band.

Sample may be applied by using the applicators provided in the kit, or by any other method whereby a small amount of test material is applied to the reaction areas.

No special patient preparation is necessary. Samples should be tested for pH within a few minutes after collection. Samples applied to the occult blood test area may be developed immediately or within four days.

Many foods (e.g., incompletely cooked meat, raw fruits and vegetables, etc.) have peroxidase activity which can produce a positive Gastroccult test result. Thus, a positive result does not always indicate the presence of human blood.

III. Reagents and Supplies

1. Materials

§ Gastroccult slides containing high-quality filter paper treated with natural guaiac resin and dyes sensitive to hydrogen ion concentration.

§ Gastroccult Developer solution contains a stabilized mixture of less than 2.9% hydrogen peroxide and 30% denatured ethyl alcohol in a citrate-buffered aqueous solution.

§ Applicators

Any lot number of developer may be used with any lot number of slides as long as both are within expiration date and are “color-matched.”

2. Storage and stability

Store slides and developer at room temperature (15-30⁰C) in original packaging. Protect from heat and light. Do not store with volatile chemicals (e.g., iodine, chlorine, bromine, or ammonia). They are stable until expiration dates, which appear on each slide and developer bottle. Do not use after expiration date.

3. Precautions

Because this test is visually read and requires color differentiation, it should not be interpreted by the visually impaired.

Gastroccult Developer should be protected from heat and the bottle kept tightly capped when not in use. It is flammable and subject to evaporation. It is also an irritant. Avoid contact with skin. DO NOT USE IN EYES. Should contact occur, rinse properly with water.

IV. Procedure

1. Properly fill out patient identification, collection date, and physician name in spaces provided on front of each slide. This is especially important to do on slides that are not to be developed immediately.

2. Open slide. Apply one drop of gastric sample to pH test circle and one drop to occult blood test area.

3. Determine pH of sample by visual comparison of test area to pH color comparator. This must be done within 30 seconds after applying sample.

4. Apply two (2) drops of Gastroccult Developer directly over the sample and one (1) drop between the positive and negative Performance Monitor areas.

5. Read occult blood results within 60 seconds. The development of any blue color in the occult blood test area is regarded as a positive result.

6. Record results appropriately on patient's chart.

V. Quality Control

The function and stability of the guaiac paper and developer can be tested using the on-slide Performance Monitor feature located to the right of the test area. The Performance Monitor areas must be developed with each patient test.

The positive Performance Monitor area contains a hemoglobin-derived catalyst which, upon application of developer, will turn blue within 10 seconds, and the color will remain stable for at least 60 seconds. The negative Performance Monitor area contains no such catalyst and should not turn blue upon application of developer.

The Performance Monitor feature provides additional assurance that the guaiac-treated paper and developer are functional. In the event that the Performance Monitor areas do not react as expected after application of developer, the test results should be regarded as invalid and unreportable. The sample should than be retested on a new slide.

If the Performance Monitors do not perform as expected, follow the steps below to troubleshoot.

STEP	ACTION
1	Do not report the patient result
2	Check expiration dates of the guaiac slides and developer
3	Review the procedure
4	Repeat control monitors with a new slide and freshly opened developer
5	If control monitors perform correctly on repeat, discard old vial of developer
6	Using a new slide repeat patient test and controls. Report patient results
7	Record all control results on the QC log and note any corrective action take, ie. opened new bottle of developer
8	If the controls do not perform correctly on repeat, call the manufacturer of Gastroccult at Smithkline Diagnostics at 1-800-877-6242. If problems continue, contact the Point-of-Care Coordinator at extension 4431.

VI. Results

§ Report and document patient results only if Performance Monitors perform as expected

§ Follow established nursing protocol on documentation of patient records

§ Gastroccult should give negative results with specimens from healthy individuals.

§ Positive results should be reported to the physician immediately.

§ The results of the Gastroccult test cannot be considered conclusive evidence of the presence or absence of upper gastrointestinal bleeding or pathology. Gastroccult tests are designed for preliminary screening as an aid to diagnosis, and are not intended to replace other diagnostic procedures.

VII. Limitations

1. Do not use Hemoccult Developer or any other developing solution.

2. Occasional gastric samples may be highly colored and appear as blue or green on the test area. Test results should only be regarded as positive if additional blue is formed after developer is added.

3. Interfering Substances are:

§ Antacids: it is unlikely that there will be any inhibition of the occult blood test by antacids if gastric samples are tested no sooner than 60 minutes after last antacid administration and following stomach irrigation.

§ Ascorbic Acid: Ascorbic acid (vitamin C) has been shown to cause false-negative test results for occult blood This can be expected to be true for the Gastroccult test also.

VIII. Competency Checks

Competency checks are performed during MYR yearly by the POC Medical Technologist or a validated nurse.

IX. References

Gastroccult package insert. SmithKline Diagnostics, Inc. San Jose, California. April 1990.