Hypocalcemia Algorithm: NP Approach

Hypocalcemia (corrected calcium < 8.5 mg/dL or ionized calcium < 4.6 mg/dL) results from PTH deficiency, PTH resistance, vitamin D deficiency/resistance, or calcium sequestration. PTH deficiency (hypoparathyroidism): most commonly post-surgical (thyroidectomy, parathyroidectomy — transient or permanent depending on parathyroid gland preservation); autoimmune (isolated or polyendocrine syndrome); congenital (DiGeorge syndrome — 22q11 deletion); infiltrative (hemochromatosis, Wilson disease, metastases). Vitamin D deficiency reduces intestinal calcium absorption (calcitriol activates TRPV6 calcium channels and calbindin in enterocytes). PTH resistance occurs in pseudohypoparathyroidism (Albright hereditary osteodystrophy — Gsα mutation preventing cAMP generation). Calcium sequestration: pancreatitis (saponification), hyperphosphatemia (CKD — calcium-phosphate precipitation), massive blood transfusion (citrate chelates calcium), hungry bone syndrome, rhabdomyolysis. The clinical manifestations of hypocalcemia result from increased neuromuscular excitability: peripheral nerve tingling → muscle cramps → carpopedal spasm → laryngospasm → seizures → cardiac arrhythmias.