SCREENING FOR OCCULT BLOOD IN STOOL SPECIMENS
PRINCIPLE
Commercially prepared occult blood test slides provide a rapid qualitative method for detecting occult blood in the stool. The test is a simplified variation of the standard guiac test for occult blood. If occult blood is present hemoglobin comes in contact with the guiac-impregnated test paper. When hydrogen peroxide solution is added, a guiac peroxidase-like reaction occurs; when occult blood is present this reaction yields a visible blue color.
Refer to video in-service presentation, Hemoccult-Developing & Interpreting the Test, located at www.beckman.com/customersupport/trainingeducation/pcdvideos.asp.
CLINICAL SIGNIFICANCE
Screening tests for fecal occult blood are intended for use as an aid in the diagnosis of asymptomatic gastrointestinal conditions such as colo-rectal cancer, ulcers, polyps, anemia and diverticulosis.
SPECIMEN
Hemoccult screening tests are requested on all patients of age 50 or older or per a medical provider’s instructions. It is recommended for screening that stool smears for testing be collected from three consecutive bowel movements since bleeding from gastrointestinal lesions may be intermittent. The occult blood screening test is performed on stool specimens smeared thinly on the two paper windows in the test slide. Hemoccult test kits are prepared in the laboratory and given to the patients at the time of their laboratory visit or when requested by their physician. Included in the occult blood test kit are:
Instruction Card (See sample below)
3 Occult Blood Test Cards
3 Wooden Sticks
3 Stool Collections Cups
The tests may be prepared and developed immediately in the health unit or prepared and held at room temperature, protected from heat and light, and sent to the laboratory for developing. (See PROCEDURE NOTES for additional information.)
PRECAUTION: Patient specimens and all materials coming into contact with them should be handled as if capable of transmitting infections and disposed of with proper precautions.
UNACCEPTABLE SPECIMENS
The following are considered unacceptable specimens:
· Unlabelled patient specimens.
· Test slides on which there is an excessive amount of stool so that the test performance monitors (See QUALITY CONTROL) cannot be read. Repeat tests should be requested in this case;
· Expired test slides or slides which have been exposed to excessive heat or light and have discolored so much that the performance monitors are not readable. Repeat tests need to be requested.
REAGENTS
Hemoccult (Smith Kline Diagnostics, Inc.) or Hemascreen (Immunostics, Inc.) or other commercially prepared slides are used for occult blood testing. These slides contain natural guiac impregnated into standardized, high quality filter paper. Supplied with the purchased slides is the developing solution, a stabilized mixture of hydrogen peroxide (less than 6%) and 75% denatured ethyl alcohol in aqueous solution.
PRECAUTION: If skin or eyes come into contact with developing solution, wash immediately with water. Do not ingest. Developing solution is flammable.
STORAGE REQUIREMENTS
· Occult Blood Test Slides should be stored at room temperature (15° - 30° C). Do not refrigerate or freeze; protect from excess heat, humidity and light. If not stored as recommended slides may discolor - turn blue - and lose sensitivity. Slides maintain sensitivity for three years after manufacture date. Do not use cards after expiration date.
· Developing Solution should be stored at room temperature (15° -30° C). Do not refrigerate or freeze. Solution remains stable for at least three years from date of manufacture. Do not use after expiration date.
CALIBRATIONS - N/A
QUALITY CONTROL
Before routine use, each lot number of test slides is tested with a hemolyzed, diluted blood sample (1 drop blood in 1ml water) to show a positive test result. This result and the results from the performance monitors (the +/-- control spots on each slide) are recorded in the Quality Control Record Book. Also, record the lot number and expiration date of every new box opened on the QC log sheet.
· The positive performance monitor contains a hemoglobin-derived catalyst, which, upon application of the developing solution, will turn blue within thirty seconds.
· The negative performance monitor contains no catalyst and should not turn blue upon application of the developing solution.
The performance monitors provide assurance that the guiac-impregnated paper and the developing solution are functional. The performance monitors are checked at the time each patient test is developed and read. It is important that the performance monitors be developed after the specimen to avoid inference or prejudice of test interpretation. If the performance monitors do not yield the proper reaction, the test is unacceptable and a repeat patient sample should be requested. A record of this action is recorded on the Quality Assurance Record.
TEST PROCEDURE
To develop the occult blood slide test:
1. Open the flap in back of the slide and apply two drops of developing solution to the guiac paper directly over each smear.
2. Read results after thirty seconds but before two minutes.
3. Apply one drop of developing solution between the positive and negative performance monitors.
4. Read results within 30 seconds. Correct results in the performance monitoring indicate the slides and the developing solution are functional. Always develop the test, read and interpret the results before adding developing solution to the performance standards. Any blue color originating from the performance standards should be ignored in interpreting the specimen test results.
CALCULATIONS – N/A
REFERENCE RANGE
This procedure is a qualitative screening for the presence of occult blood. Results are either:
Positive - Any visible blue color, which is an indication of the presence of occult blood in the stool specimen.
Negative - No blue color seen.
INTERPRETATION/REPORTING
Positive - Any trace of blue seen on or at the edge of the smears is positive for occult blood;
Negative - No blue color seen.
PROCEDURE NOTES
1. Product information indicates prepared slides should be tested within 8 days. Frequently labs receive without the specific dates of collection recorded by the patient. MED/LAB has conducted a study to demonstrate that occult blood slides yield acceptable results if testing was delayed. Six sets of slides were smeared with known negative and positive stool specimens. The slides were held at room temperature and tested at the intervals up to 50 days from date of smear preparation. See following table for results.
Test #1 (Positive) Test #2 (Negative) Performance Monitors
Positive / Negative
Day 1 + -- + / --
Day 10 + -- + / --
Day 15 + -- + / --
Day 20* + -- + / --
Day 45* + -- + / --
Day 50* + -- + / --
* Paper showed light blue discoloration but all results were readable.
Conclusion: Although patients are encouraged to return slides to the laboratory as soon as possible delays in development of the slide that are longer than 8 days do not appear to adversely affect the results of the test.
2. A special diet is omitted initially. If a patient has one or more positive tests in the initial series, the medical provider may request the patient should repeat the tests after following a special diet. A red meat free, high residue diet is recommended starting two days before testing and continuing through the test period. Raw fruits and vegetables which contain peroxidase-like substances (turnips, broccoli, horseradish cantaloupe, radishes, etc.) should be avoided during the test period.
LIMITATIONS
1. Individuals suffering from color blindness should not interpret this test.
2. Results obtained with the occult blood slides are designed for preliminary screening only and are not intended to replace diagnostic procedures such as barium enema, proctosigmoidoscopic exam or other studies. The test should not be considered as conclusive evidence for the presence or absence of gastrointestinal bleeding or pathology.
3. Some oral medications (e.g. aspirin, indomethacin, phenylbutazone, corticosteroids, reserpine) can cause G.I. irritation and occult bleeding in some patients. These substances may need to be discontinued two days prior to and during testing, as recommended by the patient’s physician.
4. Ascorbic acid in excess of 250 mg/day may cause false negative results.
5. Therapeutic dosages of iron can yield false positive fecal occult blood test reactions. Use of iron preparations should be suspended before and during testing for fecal occult blood.
REFERENCES
1. HEMASCREEN Package Insert, Immunostics, Inc. Revised 12/95.
2. HEMOCCULT Package Insert, Smith Kline Diagnostics, Inc., December, 1994.
Commercially prepared occult blood test slides provide a rapid qualitative method for detecting occult blood in the stool. The test is a simplified variation of the standard guiac test for occult blood. If occult blood is present hemoglobin comes in contact with the guiac-impregnated test paper. When hydrogen peroxide solution is added, a guiac peroxidase-like reaction occurs; when occult blood is present this reaction yields a visible blue color.
Refer to video in-service presentation, Hemoccult-Developing & Interpreting the Test, located at www.beckman.com/customersupport/trainingeducation/pcdvideos.asp.
CLINICAL SIGNIFICANCE
Screening tests for fecal occult blood are intended for use as an aid in the diagnosis of asymptomatic gastrointestinal conditions such as colo-rectal cancer, ulcers, polyps, anemia and diverticulosis.
SPECIMEN
Hemoccult screening tests are requested on all patients of age 50 or older or per a medical provider’s instructions. It is recommended for screening that stool smears for testing be collected from three consecutive bowel movements since bleeding from gastrointestinal lesions may be intermittent. The occult blood screening test is performed on stool specimens smeared thinly on the two paper windows in the test slide. Hemoccult test kits are prepared in the laboratory and given to the patients at the time of their laboratory visit or when requested by their physician. Included in the occult blood test kit are:
Instruction Card (See sample below)
3 Occult Blood Test Cards
3 Wooden Sticks
3 Stool Collections Cups
The tests may be prepared and developed immediately in the health unit or prepared and held at room temperature, protected from heat and light, and sent to the laboratory for developing. (See PROCEDURE NOTES for additional information.)
PRECAUTION: Patient specimens and all materials coming into contact with them should be handled as if capable of transmitting infections and disposed of with proper precautions.
UNACCEPTABLE SPECIMENS
The following are considered unacceptable specimens:
· Unlabelled patient specimens.
· Test slides on which there is an excessive amount of stool so that the test performance monitors (See QUALITY CONTROL) cannot be read. Repeat tests should be requested in this case;
· Expired test slides or slides which have been exposed to excessive heat or light and have discolored so much that the performance monitors are not readable. Repeat tests need to be requested.
REAGENTS
Hemoccult (Smith Kline Diagnostics, Inc.) or Hemascreen (Immunostics, Inc.) or other commercially prepared slides are used for occult blood testing. These slides contain natural guiac impregnated into standardized, high quality filter paper. Supplied with the purchased slides is the developing solution, a stabilized mixture of hydrogen peroxide (less than 6%) and 75% denatured ethyl alcohol in aqueous solution.
PRECAUTION: If skin or eyes come into contact with developing solution, wash immediately with water. Do not ingest. Developing solution is flammable.
STORAGE REQUIREMENTS
· Occult Blood Test Slides should be stored at room temperature (15° - 30° C). Do not refrigerate or freeze; protect from excess heat, humidity and light. If not stored as recommended slides may discolor - turn blue - and lose sensitivity. Slides maintain sensitivity for three years after manufacture date. Do not use cards after expiration date.
· Developing Solution should be stored at room temperature (15° -30° C). Do not refrigerate or freeze. Solution remains stable for at least three years from date of manufacture. Do not use after expiration date.
CALIBRATIONS - N/A
QUALITY CONTROL
Before routine use, each lot number of test slides is tested with a hemolyzed, diluted blood sample (1 drop blood in 1ml water) to show a positive test result. This result and the results from the performance monitors (the +/-- control spots on each slide) are recorded in the Quality Control Record Book. Also, record the lot number and expiration date of every new box opened on the QC log sheet.
· The positive performance monitor contains a hemoglobin-derived catalyst, which, upon application of the developing solution, will turn blue within thirty seconds.
· The negative performance monitor contains no catalyst and should not turn blue upon application of the developing solution.
The performance monitors provide assurance that the guiac-impregnated paper and the developing solution are functional. The performance monitors are checked at the time each patient test is developed and read. It is important that the performance monitors be developed after the specimen to avoid inference or prejudice of test interpretation. If the performance monitors do not yield the proper reaction, the test is unacceptable and a repeat patient sample should be requested. A record of this action is recorded on the Quality Assurance Record.
TEST PROCEDURE
To develop the occult blood slide test:
1. Open the flap in back of the slide and apply two drops of developing solution to the guiac paper directly over each smear.
2. Read results after thirty seconds but before two minutes.
3. Apply one drop of developing solution between the positive and negative performance monitors.
4. Read results within 30 seconds. Correct results in the performance monitoring indicate the slides and the developing solution are functional. Always develop the test, read and interpret the results before adding developing solution to the performance standards. Any blue color originating from the performance standards should be ignored in interpreting the specimen test results.
CALCULATIONS – N/A
REFERENCE RANGE
This procedure is a qualitative screening for the presence of occult blood. Results are either:
Positive - Any visible blue color, which is an indication of the presence of occult blood in the stool specimen.
Negative - No blue color seen.
INTERPRETATION/REPORTING
Positive - Any trace of blue seen on or at the edge of the smears is positive for occult blood;
Negative - No blue color seen.
PROCEDURE NOTES
1. Product information indicates prepared slides should be tested within 8 days. Frequently labs receive without the specific dates of collection recorded by the patient. MED/LAB has conducted a study to demonstrate that occult blood slides yield acceptable results if testing was delayed. Six sets of slides were smeared with known negative and positive stool specimens. The slides were held at room temperature and tested at the intervals up to 50 days from date of smear preparation. See following table for results.
Test #1 (Positive) Test #2 (Negative) Performance Monitors
Positive / Negative
Day 1 + -- + / --
Day 10 + -- + / --
Day 15 + -- + / --
Day 20* + -- + / --
Day 45* + -- + / --
Day 50* + -- + / --
* Paper showed light blue discoloration but all results were readable.
Conclusion: Although patients are encouraged to return slides to the laboratory as soon as possible delays in development of the slide that are longer than 8 days do not appear to adversely affect the results of the test.
2. A special diet is omitted initially. If a patient has one or more positive tests in the initial series, the medical provider may request the patient should repeat the tests after following a special diet. A red meat free, high residue diet is recommended starting two days before testing and continuing through the test period. Raw fruits and vegetables which contain peroxidase-like substances (turnips, broccoli, horseradish cantaloupe, radishes, etc.) should be avoided during the test period.
LIMITATIONS
1. Individuals suffering from color blindness should not interpret this test.
2. Results obtained with the occult blood slides are designed for preliminary screening only and are not intended to replace diagnostic procedures such as barium enema, proctosigmoidoscopic exam or other studies. The test should not be considered as conclusive evidence for the presence or absence of gastrointestinal bleeding or pathology.
3. Some oral medications (e.g. aspirin, indomethacin, phenylbutazone, corticosteroids, reserpine) can cause G.I. irritation and occult bleeding in some patients. These substances may need to be discontinued two days prior to and during testing, as recommended by the patient’s physician.
4. Ascorbic acid in excess of 250 mg/day may cause false negative results.
5. Therapeutic dosages of iron can yield false positive fecal occult blood test reactions. Use of iron preparations should be suspended before and during testing for fecal occult blood.
REFERENCES
1. HEMASCREEN Package Insert, Immunostics, Inc. Revised 12/95.
2. HEMOCCULT Package Insert, Smith Kline Diagnostics, Inc., December, 1994.
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