para>PO4, phosphate; N, normal; I, increased; D, decreased.
TABLE 16 " 14Variations of Various Serum and Urine Analytes in Association with Hypocalcemic DisordersView LargeTABLE 16 " 14Variations of Various Serum and Urine Analytes in Association with Hypocalcemic Disorders Hypocalcemia Associated with Increased Decreased Serum PTH Pseudohypoparathyroidism Hypoparathyroidism Renal failure, acute/chronic Acute pancreatitis Malabsorption Magnesium deficiency Vitamin D deficiency Phosphate administration Serum phosphorus Hypoparathyroidism Vitamin D deficiency Pseudohypoparathyroidism Acute pancreatitis Renal failure, acute (oliguric phase)/chronic Renal failure, acute (diuretic phase) Phosphate administration Malabsorption Serum bicarbonate and pH Hypoparathyroidism Serum Mg Renal failure, acute/chronic Magnesium deficiency Acute pancreatitis Renal failure, acute (diuretic phase) Urine calcium Hypoparathyroidism Other causes of hypocalcemia Urine phosphate Renal failure, chronic Hypoparathyroidism Vitamin D deficiency Pseudohypoparathyroidism Malabsorption Magnesium deficiency Phosphate administration Urine cAMP Renal failure, chronic Hypoparathyroidism Vitamin D deficiency Pseudohypoparathyroidism Malabsorption
- Hypoparathyroidism
- Surgical
- Idiopathic infiltration of parathyroids (e.g., sarcoid, amyloid, hemochromatosis, tumor)
- Hereditary (e.g., DiGeorge syndrome)
- Pseudohypoparathyroidism
- Chronic renal disease with uremia and phosphate retention, Fanconi syndromes, renal tubular acidosis
- Malabsorption of calcium and vitamin D, obstructive jaundice
- Insufficient calcium, phosphorus, and vitamin D ingestion
- Bone disease (osteomalacia, rickets)
- Starvation
- Late pregnancy
- Altered bound calcium citrate
- Multiple citrated blood transfusions
- Dialysis with citrate anticoagulation
- Hyperphosphatemia (e.g., phosphate enema/infusion)
- Rhabdomyolysis
- Tumor lysis syndrome
- Acute severe illness (e.g., pancreatitis with extensive fat necrosis, sepsis, burns)
- Respiratory alkalosis
- Certain drugs
- Cancer chemotherapy drugs (e.g., cisplatin, mithramycin, cytosine arabinoside)
- Fluoride intoxication
- Antibiotics (e.g., gentamicin, pentamidine, ketoconazole)
- Chronic therapeutic use of anticonvulsant drugs (e.g., phenobarbital, phenytoin)
- Loop-active diuretics
- Calcitonin
- Gadolinium-based magnetic resonance (MR) imaging contrast agents.
- Osteoblastic tumor metastases
- Neonates born of complicated pregnancies
- Hyperbilirubinemia
- Respiratory distress, asphyxia
- Cerebral injuries
- Infants of diabetic mothers
- Prematurity
- Maternal hypoparathyroidism
- Hypermagnesemia (e.g., magnesium for treatment of toxemia of pregnancy)
- Magnesium deficiency
- Toxic shock syndrome
Temporary hypocalcemia after subtotal thyroidectomy in >40% of patients; >20% are symptomatic.
Limitations
- Total serum protein and albumin should always be measured simultaneously for proper interpretation of serum calcium levels, since 0.8 mg of calcium is bound to 1.0 g of albumin in serum; to correct, add 0.8 mg/dL for every 1.0 g/dL that serum albumin falls below 4.0 g/dL; binding to globulin only affects total calcium if globulin >6 g/dL.
- Serum levels increased by
- Hyperalbuminemia (e.g., multiple myeloma, Waldenstr śm macroglobulinemia)
- Dehydration
- Venous stasis during blood collection by prolonged application of tourniquet
- Use of cork-stoppered test tubes
- Hyponatremia (<120 mEq/L), which increases the protein-bound fraction of calcium, thereby slightly increasing the total calcium (opposite effect in hypernatremia)
- Serum levels decreased by
- Hypomagnesemia (e.g., due to cisplatin chemotherapy)
- Hyperphosphatemia (e.g., laxatives, phosphate enemas, chemotherapy of leukemia or lymphoma, rhabdomyolysis)
- Hypoalbuminemia
- Hemodilution