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HPA Labs


GH stimuli include: exercise, hypoglycemia hi protein diet, acute starvation & oral contraceptives (secondary to estrogen)
GH deficiency seen in: obesity & cortico-steroid therapy
Pituitary adenoma diagnosed by: CT or MRI of brain to evaluate sella turcica
GH lab testing GH on fasting AM samples (often not diagnostic); GH Stimu tests (hyperglycemia normally suppresses GH secretion); GH remains elevated in acromegaly
3 causes of pituitary dwarfism: pit tumor (1/3); pit damage (1/3); Pure GH deficiency (1/3)
pituitary dwarfism: IGF-1 & GH Useful to compare IGF-1 levels to GH; IGF-1 is low whenever GH is deficient; IGF1 more stable than GH; mediate GH fx on sk mx
IGF-1 levels influenced by: nutrition (low levels in malnutrition)
Prolactin prodn driven by: automatic/constant unless inhibited
Most common disorder involving excess pituitary secretion Prolactinomas
ACTH measurement rarely measured directly (d/t lability)
2 actions of ADH Alters the permeability of renal collecting tubules to water; Causes vasoconstriction
ADH is secreted when serum osmo exceeds: 285 mOsm/L
Central DI: Hypothalamic origin; ADH production or release is deficient. Labs show hyperuricemia.
Nephrogenic DI: Kidneys fail to respond to normal or even elevated levels of ADH
ADH measurement usually unmeasurable; 2.3-3.1 pg/mL
Pt ADH deficient, urine osmo: ≤300 mOsmkg urine osmo: <300 mOsmkg (nml pt; ovenight urine is ≥800)
H2O deprivation test: fx of exogenous ADH Central DI: urine osmo will increase; Nephrogenic DI: urine osmo will not change
SIADH caused by: excessive levels of ADH active material of non-pituitary origin
SIADH labs: low serum osmolality (<280 mOsm/kg), low serum Na (<130mEq/L, sxs seen at <120) & high urine osmolality (>140 mOsm/kg). Low BUN & uric acid
ADH problems: tests DI: H2O deprivation; SIADH: water loading test
Water loading study results (1L H2O; hourly urine/serum x 5 hrs) Normal: urine osmo < serum osmo; SIADH: urine osmo > serum osmo
PTH labs can measure Ca, PO4, Mg, PTH directly; Alk phos assoc w/osteocyte activity (higher in growing kids, M>F, or mets)
Vit D metabolites responsible for absorption of dietary calcium & phosphate in intestines; enhance PTH fx on mobilization of skeletal Ca & PO4
Vit D labs can directly measure Vit D & metabolites
IGF's fn: IGF’s mediate the effect of GH on skeletal muscle
Labs to dx DI: No single test. 24 hr urine w/Cr (<2L/day: not DI). Serum osmo, glucose, K, Na, uric acid. UA. Serum osmo > urine osmo.
Arginine infusion test is for: growth hormone
Created by: Abarnard