The oral levothyroxine absorption test is an infrequently used test that measures intestinal absorption of free T4 to diagnose malabsorption as the cause of persistent, uncontrolled hypothyroidism. We present a case of a patient with a positive result of a 1000 mcg levothyroxine test at 2 hours, indicating malabsorption, who was then later found to have a normal response at 16 hours, calling into question the positive predictive value of the test.
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Dacus et al. (2024) studied this question.
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