Pituitary Function Test Calculator

The anterior pituitary drives (at minimum) five hormone axes -- corticotropic, thyrotropic, gonadotropic, somatotropic (GH), and lactotropic -- but this calculator screens only four of them (cortisol, thyroid, GH, prolactin) independently, each from its own baseline lab value rather than a combined score. It does not assess the gonadal axis at all: there is no LH, FSH, testosterone, or estradiol input, so the Deficient Axes Count and Panhypopituitarism Flag below are both undercounts for anyone with isolated or predominant central hypogonadism -- a patient with a failing gonadal axis plus one or two of the four modeled axes could have clinically significant hypopituitarism that this calculator's count never reaches the panhypopituitarism threshold for. The cortisol (ACTH) axis reads morning cortisol: below 3 ug/dL is very suggestive of adrenal insufficiency, above 18 ug/dL is generally considered to reasonably exclude it, and the wide band in between is genuinely indeterminate and needs a dynamic test such as a cosyntropin stimulation test or insulin tolerance test (ITT) to resolve -- note this baseline-cortisol banding applies specifically to an 8 AM morning draw, not a post-stimulation peak from a dynamic test, which would need different interpretive bands. The thyroid axis screens for CENTRAL hypothyroidism -- low free T4 paired with a low or merely normal TSH, the pattern that suggests the pituitary itself isn't driving the thyroid, as opposed to primary thyroid failure, where TSH would be appropriately elevated -- and separately flags an elevated free T4 alongside a TSH that isn't suppressed as a distinct pattern, since a healthy pituitary should suppress TSH in response to high thyroid hormone; a non-suppressed TSH with high FT4 instead suggests a TSH-secreting pituitary adenoma or thyroid hormone resistance, exactly the kind of pituitary-driven finding this calculator is meant to catch, rather than the ordinary primary hyperthyroidism pattern (elevated FT4 with a properly suppressed TSH).

Growth hormone is assessed from the peak value on a stimulation test (ITT, GHRH-arginine, or glucagon, not a single random draw, since baseline GH is not diagnostically useful), with a peak below 3 ug/L read as GH deficient and 3-5 ug/L as borderline. Prolactin is graded on its own scale, since marked elevation (above 200 ng/mL) points toward a macroprolactinoma, but this calculator also folds a macroprolactinoma-range reading into the deficient-axis count on the reasoning that a large enough mass can compress the pituitary stalk and impair the other axes even though elevated prolactin is not itself a "deficiency." Three or more affected axes (out of the four modeled here) flags possible panhypopituitarism -- keeping in mind the gonadal-axis gap above. Each axis uses a single-timepoint approximation for a real workup that typically also needs stimulation testing before treatment decisions are made.