Laboratory Findings in Calcium Disorders

• interpretation of serum calcium
• 
• Serum parathyroid hormone (PTH) concentrations in hypercalcemia and hypocalcemia
• Ca: bones
• parathyroid hormone: thief of bones
• 25-(OH)D: intestine to blood

Ca	PTH	Disease	PO4	25-(OH)D	1,25-(OH),D
up	upup	Hyperparathyroidism (1° and 3°)	down	down to normal	normal to up
up	up or normal	Familial hypocalciuric hypercalcemia	down	var.	nl
up	down	Malignancy	var	var	var.
up	down	Vitamin D excess	up	up	normal to up
up	dwon	Milk-alkali syndrome.thiazides	var	var.	var.
up	down	Bone turnover	normal to up	var	nl
------	--------------	--------------------------------------	--------------	----------------	----------------
down	upup	Pseudohypoparathyroidism	up	var	down
down	up	Vitamin D deficiency	down	down down	normal to down
down	up	Chronic renal failure (2° hyperpara)	normal to up	var	down
down	var	Acute calcium sequestration	var	var	var
down	down	Hypoparathyroidism	up	var	down to normal

Pitfalls in measuring calcium

• 生理活性鈣是游離的或電離的 (ICa)。
• Serum Ca reflects total calcium (bound + unbound) and ∴ influenced by albumin (main Ca-binding protein).
• 血清 Ca 反映總鈣（結合 + 未結合）和 所以：受白蛋白（主要 Ca 結合蛋白）的影響。
• Corrected Ca (mg/dL) = measured Ca (mg/dL) + {0.8 × [4 – albumin (g/dL)]}
• 鹼中毒會導致更多的Ca與白蛋白結合（∴總Ca可能正常但↓ICa）Alkalosis will cause more Ca to be bound to albumin (∴ total Ca may be normal but ↓ ICa)
• 最好直接測量 Ca++（但準確度取決於實驗室） Best to measure ionized Ca directly (but accuracy is lab dependent)