A rapid screening method for 1-131 fat-absorption test.

Abstract

The usual method for determining small-bowel absorbability of an oral test dose of I131-tagged triolein is to take blood samples three, four, five, and six hours after ingestion. The total blood activity in terms of percentage of administered dose is then compared with normal values. Malabsorption is considered to exist when blood activity falls below the normal range. Impairment of the body's ability to metabolize the absorbed fat is postulated when the blood activity is high and renal function is normal. Early in our routine clinical use of this test it was learned that, with oral doses of about 20 microcuries, enough activity was present in the blood at the end of three hours to be counted by means of a scintillation detector probe placed against the head. Further, a linear relationship was found to exist between the number of microcuries in the blood and the head counts. This latter finding enables reasonably accurate determination of the percentage of administered dose present in the blood without venipuncture. The examination is terminated in those patients with head counts corresponding to normal levels of absorption at the end of three hours. Venipuncture blood sampling is done at four, five, and six hours in patients with head counts indicating low blood activity at the third hour. Methods And Material The material of this study comprises 32 patients (14 male; 18 female), ranging in age from twenty-four to sixty-four years. Preparation of Patient: Twenty drops of Lugol's solution are administered to the patient the night prior to the test and nothing is taken orally after midnight. Another 20 drops of Lugol's is given the next morning followed by the triolein I131 capsule. The patient is permitted to have lunch, provided three hours have elapsed since ingestion of the capsule. Measurements: The test triolein capsule as it comes from the manufacturer is accurately assayed as to its microcurie content. This is the “administered dose.” The capsule, placed in a neck phantom for convenience, is counted at a fixed distance by the same detector probe which is used for head counts. The two-minute capsule count is referred to as “counts administered.” The scintillation detector probe is placed against the side of the head, just above the ear insertion. The net “head count” is the average of the two-minute counts on each side of the head less background, which is determined immediately after ingestion of the triolein-I131 capsule. Head counts are taken within a space of five minutes of blood withdrawal. Two milliliters of venous blood is withdrawn hourly and its activity is measured in a well counter against a standard. The number of microcuries in the 2-ml. sample multiplied by half the blood volume equals the total number of microcuries in the blood.