Table 2. Causes of hypocalcemia.^5-7.

Major causes	Sub-causes
Hypoparathyroidism	Acquired Following thyroid gland surgery either parathyroidectomy or total thyroidectomy (where parathyroid gland is damaged) Infiltrative disease (e.g., hemochromatosis, granulomatous disease (sarcoidosis), thalassemia, and amyloidosis) Metastatic or heavy metal (copper, iron) infiltration of parathyroid gland Due to an autoimmune disease (isolated or often as part of polyglandular autoimmune syndromes) Pseudohypoparathyroidism types 1a, 1b, and 2 Genetic cause Absence of parathyroid glands at birth/developmental defects of parathyroid glands (DiGeorge's syndrome - aplasia of third and fourth pharyngeal pouch) Autosomal dominant hypocalcemia (activating mutation of calcium receptor gene)
Pseudohypoparathyroidism	Lack of response to normal level of PTH
Calcium disorders	Calcium-sensing receptor mutations Inadequate calcium in diet/dietary Ca deficiency cow's milk protein intolerance The natural aging process with increasing parity can cause calcium deficiency disease Disorder that decreases calcium absorption or serum calcium concentration by binding of calcium within the vascular space or by its deposition in tissues, as can occur with short gut, hyperphosphatemia, coeliac disease, tufting enteropathy Renal disease making kidneys excrete more calcium in urine Hungry bone syndrome (persistent hypocalcemia and hypophosphatemia post parathyroidectomy) Acid-base disturbances can cause hypocalcemia (in cases of alkalosis, as the blood's pH rises (low hydrogen cations), this results in an ionization of albumin, making in more negative. Thus, calcium binds to albumin with greater affinity, and this reduces the free calcium) Increased potassium can burn up calcium (potassium aids in maintaining the body’s normal blood calcium balance by decreasing the loss of calcium through urine)
Actual vitamin D deficiency and dependency	Dietary deficiency Lack of sunlight Malabsorption, especially pancreatic disease and coeliac disease
Functional vitamin D deficiency and dependency	Renal disease causes kidneys to lower conversion and activation of vitamin D (lack of 1- α hydroxylation) Liver disease (lack of 25-hydroxylation)
Medication effects	Corticosteroids alter vitamin D Infusion of phosphate or citrated blood transfusion May occasionally develop in the course of treatment with commonly used drugs like antiepileptics and proton pump inhibitors. Such incidents of hypocalcemia can be easily missed due to the coexistence of multiple causative factors
Severe hypomagnesemia inhibits PTH response to hypocalcemia	Renal loss Diuretics, especially loop diuretics Immunosuppressants Miscellaneous drugs, e.g., proton pump inhibitors Gastrointestinal Severe diarrhea Malnutrition Alcoholism
Other causes	Sclerotic metastases Acute pancreatitis (when lipolytic products released from the inflamed pancreas chelate calcium) Fanconi syndrome Septic shock (due to suppression of parathyroid hormone release and decreased vitamin D conversion) Severe hypermagnesemia Surgery Post bariatric surgery Hyperphosphatemia (causes hypocalcemia by poorly understood mechanisms) Renal failure Rhabdomyolysis Tumor lysis Phosphate administration Hypoalbuminemia (most common cause of hypocalcemia) Cirrhosis, nephrosis, malnutrition, burns, chronic illness, and sepsis Widespread osteoblastic metastases Breast cancer