Calcium (CA), Serum

CPT Code:  



Serum (preferred) or plasma 


1 mL 

Minimum Volume:  0.5 mL 

Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube; do not use oxalate, EDTA, or citrate plasma.


Spectrophotometry (SP)


Serum should be separated from red cells and analyzed promptly. Complete clot formation should take place before centrifugation. 

Patient Preparation: 

Morning, fasting sample is desirable, since some diurnal variation exists (which may reflect postural changes). 

Reference Range: 

8.5-10.1 mg/dL 


Temperatures  Period 
Room Temperature  8 Hours 
Refrigerated (2-8 ⁰C)  2 Days 
Frozen (≤ -20 ⁰C)  Longer Storage 


Use Calcium is the most important mineral in the body with approximately 98% found in the bones. The calcium in the blood is necessary for many important bodily functions, including muscle contraction, blood clotting, bone formation, conduction of nerve impulses, and parathyroid gland activity. Blood calcium levels are strictly regulated by various substances called hormones. 
Clinical Significance High Calcium may be caused by hyperparathyroidism, Carcinoma, with or without bone metastases, myeloma, leukemia and lymphoma, dehydration, sarcoidosis, chronic hypervitominosis D, vitamin A intoxication,  prolonged immobilization, TB, histoplasmosis, coccidioidomycosis, berylliosis, milk-alkali syndrome, Idiopathic hypercalcemia of infancy (uncommon), addison disease, acromegaly, pheochromocytoma, advanced chronic liver disease, bacteremia, familialhypocalciuric hypercalcemia or aluminum induced renal osteomalacia, rhabdomyolysis.  Several commonly used drugs cause in vivo elevation, including calcium salts, lithium, thiazide/chlorthalidone therapy, other diuretics; vitamins D and A and estrogens (rapid increase in patients with breast carcinoma).

Low Calcium may be the cause of vitamin D deficiency, rickets, osteomalacia, milkman syndrome, renal tubular acidosis, acute pancreatitis, Dilutional (I.V.) fluids, bacteremia, hypomagnesemia, renal insufficiency, hypoparathyroidism, or pseudohypoparathyroidism.  In addition, low albumin and low total protein relate to common, usually slight decreases of calcium.

Causes for Rejection:  Gross hemolysis; EDTA, oxalate, or citrate anticoagulant; improper labeling 
Limitations Sodium citrate, EDTA, and NaF potassium oxalate interfere. 
Interfering Substances:  Interference due to magnesium is negligible at magnesium levels normally encountered in human serum.  A maximum positive interference of 0.7 mg/dL occurs at a magnesium level of 7 mg/dL.

Calcium values may be falsely decreased in the presence of gadolinium-containing contrast agents such as Omniscan.  Therefore it is recommended to avoid drawing samples for serum calcium determination 24 hours after administration of Omniscan. 

Bilirubin (unconjugated) of 80mg/dL decreases calcium at 6.4mg/dL by 11%.

Lipemia of 600mg/dL, the magnitude of the interference could not be determined.