Folic Acid Absorption Determined by a Single Stool Sample Test—A Double-Isotope Technique. The Folic Acid Absorption Capacity in Children

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Abstract
The fractional folic acid absorption (FAFol) was determined in 66 patients with various gastrointestinal diseases by a double-isotope technique, employing a single stool sample test (SSST) as well as a complete stool collection. The age of the patients ranged from 2.5 months to 16.8 years (mean 6.3 years). The test dose was administered orally and consisted of 50 .mu.g of [3H]folic acid (monoglutamate) (.apprx. 20 .mu.Ci), carmine powder, and 2 mg 51CrCl3( .apprx. 1.25 .mu.Ci) as the unabsorbable tracer. The whole-body radiation given to a 1-year-old child averaged 4.8 mrad only. The stool and napkin contents were collected and homogenized by the addition of 300 ml chromium sulfuric acid. A 300-ml sample of the homogenized stool and napkin contents, as well as 300 ml chromium sulfuric acid (75% vol/vol) containing the standards, were counted for the content of 51Cr in a broad-based well counter. The quantity of [3H]folic acid was determined by liquid scintillation, after duplicate distillation. Estimated by SSST, the FAFol, which employs the stool with the highest content of 51Cr corresponding to the most carmine-colored stool, correlated closely with the FAFol based on complete stool collection (r = 0.96, n = 39, p < 0.0001). The reproducibility of FAFol determined by SSST was assessed from repeated tests in 18 patients. For a mean of 81%, the SD was 4.6%, which corresponded to a coefficient of variation of 5.7%. The excretion of 51CrCl3 and 3H in the urine was examined in six patients with moderate to severe mucosal damage and was found to be low. The mean FAFol in 45 control children aged 9 months to 16.8 years (mean 6.4 years) was 83% (range 66-95%). The FAFol levels showed no correlation with age. In conclusion, the method fulfilled the following requirements: (a) a minimum of cooperation and control of possible errors, (b) small radiation dose, (c) direct measurement of the folic acid absorption, and (d) no need for flushing with folic acid. To the best of the author''s knowledge, this study is the first attempt of direct measurement of folic acid absorption in control children.