Reference Intervals for Intestinal Disaccharidase Activities Determined from a Non-Reference Population

Background: Cutoff activities for diagnosing disaccharidase deficiencies are historical and are difficult to verify from a reference population. The objectives of this study were to validate the utility of historical disaccharidase cutoffs using data from clinical samples and to evaluate the demographics of individuals for whom intestinal disaccharidase testing was performed. Methods: Results from 14,827 disaccharidase test samples were extracted from the laboratory information system. Data were analyzed by the Hoffman method to calculate a reference interval for each enzyme, and the lower limits were compared to historical cutoffs. The observed frequencies of disaccharidase deficiencies were determined using historic and calculated cutoffs. Results: Themedian patient age of the entire data set was 13 years (range <1–88 years), and 45%were male. The cutoffs for lactase,maltase, palatinase, and sucrasewere determined to be 10, 100, 9, and 25 U/g protein, respectively. Applying these cutoffs to the data set, 61% had no enzyme deficiencies, 35% were lactase deficient, 11% were maltase deficient, 13% were palatinase deficient, and 13% were sucrase deficient. Pandisaccharidase deficiency was present in 8%. Conclusions: Disaccharidase testing is most commonly performed in patients <18 years. Lactase deficiency is the most frequently observed single-disaccharidase deficiency. The historical cutoffs for maltase and sucrase were validated. To align with calculated reference intervals, the palatinase cutoff should increase from 5 to 9 U/g protein, and the lactase cutoff should decrease from 15 to 10 U/g protein.