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HPA Labs
Endocrine
| Question | Answer |
|---|---|
| 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
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