25-hydroxy vitamin D absorption test in patients with gastrointestinal disorders.

To evaluate the relationships of a 25-hydroxy vitamin D absorption test to intestinal fat absorption and to the absorption of radioactively labeled vitamin D and 25-hydroxy vitamin D, an investigation was undertaken in 19 patients with gastrointestinal disorders. A correlation was noted between the results of the 25-hydroxy vitamin D absorption test and baseline 25-hydroxy vitamin D levels. No correlation was found between results of the 25-hydroxy vitamin D absorption test and quantitative fecal fat excretion. Peak values of the 25-hydroxy vitamin D absorption test correlated with net absorption of 14C vitamin D. No correlation existed between the values obtained in the 25-hydroxy vitamin D absorption test and 3H-25-OH D absorption. These studies indicate that the 25-hydroxy vitamin D absorption test probably does not serve as an effective screening test for intestinal fat malabsorption. The results of the test probably most accurately reflect the body stores of vitamin D at the time of testing, but there appears to be little advantage to performing a 25-hydroxy vitamin D absorption test in lieu of a single determination of the serum level of 25-hydroxy vitamin D as a method of evaluating vitamin D nutritional status.