What is the best workup for hypocalcemia?

Unexplained hypocalcemia can usually be diagnosed by a limited number of serum tests when the cause isn't obvious from the history (recent neck surgery or renal failure): calcium corrected for serum albumin); creatinine; phosphorus; magnesium; parathyroid hormone (PTH). The most common causes, categorized according to the results of these tests, are (strength of recommendation: C, expert opinion, case series, and physiologic principles): high PTH, high phosphorus, and high creatinine: renal failure; high PTH, low or normal phosphorus, and normal creatinine: vitamin D deficiency or pancreatitis; low PTH, high phosphorus, and normal creatinine: inadequate parathyroid gland function or hypomagnesemia