Calcium in blood
Test Description
Calcium (Ca++) is present in the blood in two forms. Approximately 50% is present
in a free state, and the other 50% is bound to plasma protein, primarily to albumin.
The calcium which is circulating in the free state is biologically active. Its functions
include important roles in muscle contraction, heart function, transmission of nerve
impulses, and clotting of the blood.
The amount of calcium in the blood is minute compared to the 98% to 99% present
in the teeth and bones. The storage of calcium in the bones provides an excellent
reservoir which is readily available for release into the bloodstream to assist in
maintaining a normal level of calcium in the blood.
Two hormones work together to control serum calcium levels. Calcitonin, which
is secreted by the thyroid gland, causes calcium to be excreted by the kidneys, thus
preventing a calcium excess in the blood. Parathyroid hormone (PTH) works directly
on the bones to release calcium into the bloodstream when needed and also
increases absorption of calcium by the intestines and kidneys. There is an inverse
relationship between calcium and phosphorus: as serum calcium levels increase,
serum phosphorus levels decrease.
This laboratory test measures the total calcium present in the blood. This provides
information regarding parathyroid gland function and the metabolism of calcium.
It is also used to evaluate malignancies, since cancer cells release calcium,
often resulting in high calcium levels in the blood (hypercalcemia).
Since much of the circulating calcium is bound to albumin, calcium levels in the
blood must be interpreted in relation to serum albumin levels. As serum albumin
decreases 1 g, the total serum calcium decreases approximately 0.8 mg due to the
decrease in the bound calcium; the amount of free calcium would not change.
Patients with hypercalcemia may have deep bone pain, renal calculi, and muscle
hypotonicity. Patients with hypocalcemia, or decreased serum calcium levels,
may experience numbness and tingling in the hands, feet, and around the mouth, muscle
twitching, cardiac arrhythmias, and possibly convulsions. These patients may
also demonstrate Chvostek’s sign and Trousseau’s sign.
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Normal Values
8.5–10.5 mg/dL (2.1–2.6 mmol/L SI units)
Elderly: Decreased
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Possible Meanings of Abnormal Values
Increased Decreased
Acromegaly Acute pancreatitis
Addison’s disease Alcoholism
Antacid abuse Chronic renal disease
Dehydration Diarrhea
Hodgkin’s disease Early neonatal hypocalcemia
Hyperparathyroidism Hyperphosphatemia
Hyperthyroidism Hypoparathyroidism
Prolonged immobilization Low albumin level
Leukemia Malabsorption
Lung cancer Massive blood transfusions
Metastatic bone cancer Metabolic alkalosis
Multiple myeloma Osteomalacia
Paget’s disease Renal failure
Parathyroid tumor Rickets
Renal cancer Severe malnutrition
Respiratory acidosis Vitamin D deficiency
Sarcoidosis
Vitamin D intoxication
Williams syndrome
ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Contributing Factors to Abnormal Values
• Use of a tourniquet during the acquisition of the blood sample causes venous stasis.
This may alter test results.
• Drugs which may increase blood calcium levels: anabolic steroids, androgens,
antacids, calcium carbonate, calcium gluconate, calcium salts, ergocalciferol, estrogens,
hydralazine, indomethacin, lithium, parathyroid hormone, progesterone,
tamoxifen, theophylline, thiazide diuretics, thyroid hormones, vitamin A, vitamin D.
• Drugs which may decrease blood calcium levels: acetazolamide, antacids, anticonvulsants,
asparaginase, aspirin, barbiturates, calcitonin, cisplatin, corticosteroids,
cholestyramine, furosemide, gastrin, gentamicin, glucagon, glucose, heparin, hydrocortisone,
insulin, iron, laxatives, loop diuretics, magnesium salts, mercurial diuretics,
methicillin, phenobarbital, phenytoin, sulfonamides.
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Interventions/Implications
Pretest
• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• No fasting is usually required prior to the test, although some laboratories do require a
fast with water permitted.
Procedure
• A 7-mL blood sample is drawn in a red-top collection tube. Use of a tourniquet is
avoided, if possible.
• Gloves are worn throughout the procedure.
Posttest
• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Clinical alert
• Patients with low calcium levels should be informed of dietary sources of calcium:
milk, cheese, turnip greens, collard greens, white beans, and lentils.
• Infants with Williams syndrome can have critically high calcium levels due to
idiopathic hypercalcemia. This tends to resolve as the child gets older, but may
necessitate use of calcium-free formula during infancy and early childhood
Calcium (Ca++) is present in the blood in two forms. Approximately 50% is present
in a free state, and the other 50% is bound to plasma protein, primarily to albumin.
The calcium which is circulating in the free state is biologically active. Its functions
include important roles in muscle contraction, heart function, transmission of nerve
impulses, and clotting of the blood.
The amount of calcium in the blood is minute compared to the 98% to 99% present
in the teeth and bones. The storage of calcium in the bones provides an excellent
reservoir which is readily available for release into the bloodstream to assist in
maintaining a normal level of calcium in the blood.
Two hormones work together to control serum calcium levels. Calcitonin, which
is secreted by the thyroid gland, causes calcium to be excreted by the kidneys, thus
preventing a calcium excess in the blood. Parathyroid hormone (PTH) works directly
on the bones to release calcium into the bloodstream when needed and also
increases absorption of calcium by the intestines and kidneys. There is an inverse
relationship between calcium and phosphorus: as serum calcium levels increase,
serum phosphorus levels decrease.
This laboratory test measures the total calcium present in the blood. This provides
information regarding parathyroid gland function and the metabolism of calcium.
It is also used to evaluate malignancies, since cancer cells release calcium,
often resulting in high calcium levels in the blood (hypercalcemia).
Since much of the circulating calcium is bound to albumin, calcium levels in the
blood must be interpreted in relation to serum albumin levels. As serum albumin
decreases 1 g, the total serum calcium decreases approximately 0.8 mg due to the
decrease in the bound calcium; the amount of free calcium would not change.
Patients with hypercalcemia may have deep bone pain, renal calculi, and muscle
hypotonicity. Patients with hypocalcemia, or decreased serum calcium levels,
may experience numbness and tingling in the hands, feet, and around the mouth, muscle
twitching, cardiac arrhythmias, and possibly convulsions. These patients may
also demonstrate Chvostek’s sign and Trousseau’s sign.
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Normal Values
8.5–10.5 mg/dL (2.1–2.6 mmol/L SI units)
Elderly: Decreased
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Possible Meanings of Abnormal Values
Increased Decreased
Acromegaly Acute pancreatitis
Addison’s disease Alcoholism
Antacid abuse Chronic renal disease
Dehydration Diarrhea
Hodgkin’s disease Early neonatal hypocalcemia
Hyperparathyroidism Hyperphosphatemia
Hyperthyroidism Hypoparathyroidism
Prolonged immobilization Low albumin level
Leukemia Malabsorption
Lung cancer Massive blood transfusions
Metastatic bone cancer Metabolic alkalosis
Multiple myeloma Osteomalacia
Paget’s disease Renal failure
Parathyroid tumor Rickets
Renal cancer Severe malnutrition
Respiratory acidosis Vitamin D deficiency
Sarcoidosis
Vitamin D intoxication
Williams syndrome
ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Contributing Factors to Abnormal Values
• Use of a tourniquet during the acquisition of the blood sample causes venous stasis.
This may alter test results.
• Drugs which may increase blood calcium levels: anabolic steroids, androgens,
antacids, calcium carbonate, calcium gluconate, calcium salts, ergocalciferol, estrogens,
hydralazine, indomethacin, lithium, parathyroid hormone, progesterone,
tamoxifen, theophylline, thiazide diuretics, thyroid hormones, vitamin A, vitamin D.
• Drugs which may decrease blood calcium levels: acetazolamide, antacids, anticonvulsants,
asparaginase, aspirin, barbiturates, calcitonin, cisplatin, corticosteroids,
cholestyramine, furosemide, gastrin, gentamicin, glucagon, glucose, heparin, hydrocortisone,
insulin, iron, laxatives, loop diuretics, magnesium salts, mercurial diuretics,
methicillin, phenobarbital, phenytoin, sulfonamides.
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Interventions/Implications
Pretest
• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• No fasting is usually required prior to the test, although some laboratories do require a
fast with water permitted.
Procedure
• A 7-mL blood sample is drawn in a red-top collection tube. Use of a tourniquet is
avoided, if possible.
• Gloves are worn throughout the procedure.
Posttest
• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Clinical alert
• Patients with low calcium levels should be informed of dietary sources of calcium:
milk, cheese, turnip greens, collard greens, white beans, and lentils.
• Infants with Williams syndrome can have critically high calcium levels due to
idiopathic hypercalcemia. This tends to resolve as the child gets older, but may
necessitate use of calcium-free formula during infancy and early childhood
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