Serum calcium

Alternative names 
Ca+2; Calcium - serum; Ca++

Serum calcium is a blood test that measures calcium in serum. Serum calcium is usually measured to screen for or monitor diseases of the bone or calcium regulation disorders (diseases of the parathyroid gland or kidneys).

How the test is performed

Adult or child:
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test
Drugs that can cause increased measurements in this test include calcium salts (for example, in nutritional supplements or antacids), vitamin D, lithium, thiazide diuretics, and thyroxine. Consult your health care provider regarding the need to discontinue drugs that may affect this test.

Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

  • Infant test or procedure preparation (birth to 1 year)  
  • Toddler test or procedure preparation (1 to 3 years)  
  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed
All cells require calcium for numerous functions. Calcium is especially important in the structure of bones and in the neuromuscular activity. A deficiency of calcium in the body fluids causes hyperexcitable nerves and muscles. Excess calcium has the opposite effect.

Normal Values
Normal values range from 8.5 to 10.2 mg/dL. Normal value ranges may vary slightly among different laboratories.

What abnormal results mean

Abnormal results indicate the following:

Greater-than-normal levels may indicate:

  • Hyperparathyroidism  
  • Metastatic bone tumor  
  • Milk-alkali syndrome  
  • Multiple myeloma  
  • Paget’s disease  
  • Sarcoidosis  
  • Tumors producing a PTH-like substance  
  • Vitamin D intoxication

Lower than normal levels may indicate:

  • Hypoparathyroidism  
  • Malabsorption (inadequate absorption of nutrients from the intestinal tract)  
  • Osteomalacia  
  • Pancreatitis  
  • Renal failure  
  • Rickets and vitamin D deficiency

Additional conditions under which the test may be performed:

  • Delirium  
  • Dementia  
  • Multiple endocrine neoplasia (MEN) II  
  • Multiple endocrine neoplasia (MEN) I  
  • Renal cell carcinoma  
  • Secondary hyperparathyroidism

What the risks are

  • Excessive bleeding  
  • Fainting or feeling lightheaded  
  • Hematoma (blood accumulating under the skin)  
  • Infection (a slight risk any time the skin is broken)  
  • Multiple punctures to locate veins

Special considerations
An excess ingestion of milk or vitamin D as a dietary supplement can increase calcium levels.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Johns Hopkins patient information

Last revised: December 2, 2012
by Arthur A. Poghosian, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.