The PMOS diagnostic workup: Labs, rule-outs, and timing tips
Which labs actually change management? Our experts debate fasting insulin versus A1c, explain why total testosterone can mislead, and share the LH-to-FSH trick that helps settle ambiguous cases.
Maresca walks through her diagnostic approach, starting with ruling out mimics: Cushing's syndrome (thick violaceous striae, buffalo hump, facial redness, hypertension), nonclassic congenital adrenal hyperplasia, and hypothyroidism, which can also disrupt cycles. Once PMOS is confirmed, she screens for associated metabolic complications with a lipid panel, liver function tests, blood pressure, and a sleep study when obstructive sleep apnea is suspected. On insulin testing, she says fasting insulin levels rarely change management, since insulin secretion fluctuates constantly; she relies instead on HDL, triglycerides, and hemoglobin A1c, reserving a 2-hour glucose tolerance test for patients borderline on A1c who could still have elevated post-prandial glucose. Cree agrees fasting insulin is largely unhelpful and notes that in her 19-center research cohort, only two sites still run oral glucose tolerance tests routinely; the rest use A1c. Citing the TODAY and RISE trials, which showed pediatric type 2 diabetes progresses aggressively and resists delay once A1c reaches 6%, she keeps a low threshold for metformin, treating every adolescent with PMOS as functionally insulin resistant. Both physicians flag sex hormone binding globulin (SHBG) as a key marker: when SHBG runs low from insulin resistance, total testosterone can look falsely normal even though free testosterone is elevated, making a full androgen panel, not total testosterone alone, essential. Cree adds two more diagnostic habits outside formal guidelines: ruling out a prolactinoma and primary ovarian failure with FSH, and checking LH, since roughly 80% of adolescents with PMOS have an LH higher than FSH, a pattern she uses to tip ambiguous cases. Because testosterone follows a diurnal rhythm, she recommends redrawing afternoon labs the following morning. Maresca adds that DHEA sulfate catches androgen elevations that testosterone alone misses; Cree's data show 10% of adolescents nationally have an isolated DHEAS elevation.