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Lab Test: Calcium (Blood) Level

    Lab Test
    • Lab Test: Calcium (Blood) Level
    • Detection of ionized calcium in serum, plasma or whole blood for the evaluation and management of metabolic and endocrine disorders.
    • Used to monitor patients with renal failure renal transplantation, hyperparathyroidism, and various malignancies.
    • Used to monitor calcium levels during and after large-volume blood transfusions.
    Reference Range
    • Ionized calcium:
      • Adults (whole blood):  4.5-5.6 mg/dL (1.1-1.4 mmol/L)
      • Adults (plasma):  4.12-4.92 mg/dL (1.03-1.23 mmol/L)
      • Adults (serum):  4.64-5.28 mg/dL (1.16-1.32 mmol/L)
      • Adults, 60-90 years (whole blood):  4.64-5.16 mg/dL (1.16-1.29 mmol/L)
      • Adults > 90 years (whole blood):  4.48-5.28 mg/dL (1.12-1.32 mmol/L)
      • Neonates, cord blood (serum):  5.2-6.4 mg/dL (1.3-1.6 mmol/L)
      • Neonates, 2 hours (serum):  4.84-5.84 mg/dL (1.21-1.46 mmol/L)
      • Neonates, 24 hours (serum):  4.4-5.44 mg/dL (1.1-1.36 mmol/L)
      • Neonates, 6 to 36 hours (capillary blood): 4.2-5.48 mg/dL (1.05-1.37 mmol/L)
      • Neonates, 60 to 84 hours (capillary blood):  4.4-5.68 mg/dL (1.1-1.42 mmol/L)
      • Neonates, 3 days (serum):  4.6-5.68 mg/dL (1.15-1.42 mmol/L)
      • Neonates, 5 days (serum):  4.88-5.92 mg/dL (1.22-1.48 mmol/L)
      • Neonates, 108 to 132 hours (capillary blood): 4.8-5.92 mg/dL (1.2-1.48 mmol/L)
      • Children (serum):  4.9-5.52 mg/dL (1.2-1.38 mmol/L)
    • Total calcium:
      • < 10 days:  7.6-10.4 mg/dL (1.9-2.60 mmol/L
      • Umbilical:  9.0-11.5 mg/dL (2.25-2.88 mmol/L)
      • 10 days - 2 years:  9.0-10.6 mg/dL (2.3-2.65 mmol/L)
      • Child:  8.8-10.8 mg/dL (2.2-2.7 mmol/L)
      • Adult:  9.0-10.5 mg/dL (2.25-2.62 mmol/L)
    • Critical Values
      • Total calcium:  < 6 or > 13 mg/dL or <1/5 or > 3.25 mmol/L (SI units)
      • Ionized calcium:  < 2.2 or > 7 mg/dL or <0.78 or > 1.58 mmol/L (SI units)
    Indications & Uses
    • Ionized calcium monitoring in critically ill patients - provides the most accurate assessment of calcium status in the critically ill patient.  An ionized calcium level lower than 1.15 mmol/L is indicative of hypocalcemia.
      • Low critical limits for ionized calcium range from 2 to 4.29 mg/dL (0.5 -1.07 mmol/L) in US medical centers and from 2.4 to 4.33 mg/dL (0.6-1.08 mmol/L) in US children's hospitals.
      • High critical limits for ionized calcium range from 5.21 to 8.02 mg/dL (1.3-2 mmol/L) in US medical cent3rs and from 5.41 to 7.01 mg/dL (1.35-1.75 mmol/L) in US children's hospitals. 
      • Symptoms of hypercalcemia usually occur once ionized calcium levels are above 1.5 mmol/L. 
    • Suspected hyperparathyroidism - elevated serum ionized calcium in association with raised parathyroid hormone (PTH) levels strongly suggests hyperparathyroidism. 
    • Suspected hypoparathryoidism - decreased serum ionized calcium associated with low PTH and high serum phosphate levels suggests hypoparathroidism.  Ionized calcium levels should be maintained at the lower limit of normal (about 1.15 mmol/L) in patients with surgical hypoparathroidism to reduce risk of hypercalcemic episodes.
    Clinical Application
    • Serum calcium is necessary in many metabolic enzymatic pathways.  The serum calcium test is used to evaluate parathyroid function and calcium metabolism by directly measuring the total amount of calcium in the blood. 
    • The ionized form of calcium also can be measured by ion-selective electrode techniques or can be calculated from several available formulas.  An advantage of measuring the ionized form is that it is unaffected by changes in serum albumin levels. 
    • When the serum calcium level is elevated on at least three separate determinations the patient is said to have hypercalcemia. 
    • Increased levels (hypercalcemia) may indicate:
      • Hyperparathyroidism, nonparathyroid PTH-producing tumor (e.g., lung or renal carcinoma), metastatic tumor to bone, Paget disease of bone, prolonged immobilization, milk-alkali syndrome, Vitamin D intoxication, lymphoma, multiple myeloma, granulomatous infections such as sarcoidosis and tuberculosis, Addison disease, acromegaly, or hyperthyroidism. 
    • Decreased levels (hypocalcemia) may indicate: 
      • Hypoparathyroidism, renal failure hyperphosphatemia secondary to renal failure, rickets, Vitamin D deficiency, osteomalacia, hypoalbuminemia, malabsorption, pancreatitis, fat embolism, or alkalosis.
    Related Tests
    • Parathyroid hormone - a measurement of PTH, which increases serum calcium levels.
    • Albumin - has a major effect on serum calcium metabolism
    • Vitamin D - adequate levels of this vitamin are required for calcium absorption
    Drug-Lab Interactions
    • Vitamin D intoxication may cause increased calcium levels.
    • Excessive ingestion of milk may cause increased levels.
    • Serum pH can affect calcium values.  A decrease in pH causes increased calcium levels.
    • Prolonged tourniquet time will lower pH and factitiously increase calcium levels.
    • There is normally a small diurnal variation in calcium, with peak levels occurring around 9 PM.
    • Hypoalbuminemia is associated with decreased levels of total calcium.
    • Drugs that may cause increased levels include:  alkaline antacids, androgens, calcium salts, ergocalciferol, hydralazine, lithium, PTH, thiazide diuretics, thyroid hormone, and vitamin D.
    • Drugs that may cause decreased levels include:  acetazolamide albuterol, anticonvulsants, asparaginase, aspirin, calcitonin, cisplatin, corticosteroids, estrogens, heparin, laxatives, loop diuretics, magnesium salts, oral contraceptives, and thiazide diuretic.
    Test Tube Needed
    • Heparinized tube* (PDR); red top tube
    • Collect anaerobic sample. 
    • Use heparinized tube for whole blood sample collection.
    • Draw sample from non-static limb.
    • Avoid prolonged tourniquet use.
    • Draw whole blood for emergent care samples, anticoagulate with less than 15 International units/mL of calcium-0titrated heparinate, and process within 15 minutes.
    • Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding.
    Storage and Handling
    • Put sample on ice and deliver to laboratory promptly.
    • Store plasma or serum at -20°C for up to 6 months.
    What To Tell Patient Before & After
    • Explain the procedure to the patient.
    • Tell the patient that no fasting is required; however, the serum calcium may be part of a multichemical analysis in which fasting is required for the other studies.
    • LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.
    • Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.

MESH Terms & Keywords

  • Calcium