CRITICAL ANALYSIS OF THE ACCURACY OF A COMBINED TEST (SE-75-HCAT AND CO-58 B-12) OF ILEAL FUNCTION USING A WHOLE-BODY COUNTER

The accuracy of a combined test (**7**5Se-HCAT plus **5**8Co-B//1//2) of ileal function by whole-body counting has been assessed with particular attention being paid to the reliability of the 100% retention measurements, the accuracy of the crossover of **5**8Co into the **7**5Se channel and the effects of variable counting geometry. A linear relationship between **5**8Co crossover and body weight improved the accuracy of determining the crossover value for individual patients. The main sources of error were due to problems of variable counting geometry but there was very good agreement between **7**5Se and **5**8Co retentions measured by whole body counting and by excreta analysis which suggested that the overall error of the test was unlikely to exceed plus or minus 10%. A protocol is presented for use of the combined test on an outpatient basis and includes retention measurements at 4, 7, and 10 d post administration.