5C61.60/E73 Primary lactase deficiency



Primary lactase deficiency is caused by a genetic mutation that reduces the activity of the lactase enzyme, which is responsible for breaking down lactose, a sugar found in dairy products.


Primary lactase deficiency is diagnosed by a simple breath test that measures the amount of hydrogen present in the breath when a patient consumes lactose.

Differential diagnosis

Differential diagnoses for primary lactase deficiency include secondary lactase deficiency, which can be caused by a variety of conditions such as celiac disease, Crohn’s disease, and small intestinal bacterial overgrowth; and congenital lactase deficiency, which is a rare inherited disorder.


Treatment for primary lactase deficiency involves eliminating or reducing lactose in the diet and taking over-the-counter lactase supplements.


The prognosis for primary lactase deficiency is generally good, as long as patients follow their doctor’s recommendations for dietary changes and lactase supplementation.

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