Ionized calcium
(Factor IV)

Calcium in the fifth most common element and the most prevalent cation found in the body. Calcium exists in three physiochemical states in plasma: free/ionized, bound and complexed with small anions. Ionized calcium is a more useful measure than total calcium and provides the best indication of calcium status because it is biologically active and is tightly regulated by hormones. Calcium is used for the assessment and treatment of parathyroid disease, a variety of bone diseases and chronic renal disease.

Sample Type:

Whole blood Green Top (lithium heparin)

Uses:

• To measure the coagulation factor concentration in the blood.

• To find the inherited or acquired bleeding disorders.

• If there is a history of bruises or excessive bleeding.

• If there are prolonged PT or PTT.

• Acquired conditions like Vit. K deficiency or liver disease.

• Maybe advised to monitor the treatment of a patient with factor deficiency.

Precautions:

• Fasting sample is preferred.

• Venous stasis or upright posture increased the calcium level by 0.6 mg / dL.

• There is diurnal variation, greater in PM than in AM.

• Separate immediately from red blood cells to avoid calcium absorption by these cells (red blood cells).

• Excessive milk intake leads to an increase in calcium levels.

• Vitamin D poisoning also increases the level of calcium.

• Check the level of albumin because hypoalbuminemia leads to an artificial decrease in the level of calcium

• Drugs can increase the level of serum calcium such as calcium salts, alkaline antacids, thiazide diuretics, vitamin D, parathyroid and thyroid hormones and androgens.

• Drugs can lower the level of calcium such as aspirin, anticonvulsants, heparin, laxatives, diuretics, magnesium salts and oral contraceptives.

Interfering factors:

Calcium blood levels depend on several important factors, including:

• Parathyroid hormone (PTH)

• Vitamin D

• Phosphorous

• Magnesium

• Thiazide diuretics may impair urinary calcium excretion and result in hypercalcemia (most common drug-induced factor).

• For patients with renal insufficiency undergoing dialysis, a calcium-ion exchange resin is sometimes used for hyperkalemia. This resin may increase calcium levels.

• Increased magnesium and phosphate uptake and excessive use of laxatives may lower blood calcium level because of increased intestinal calcium loss.

• When decreased calcium levels are due to magnesium deficiency (as in poor bowel absorption), the administration of magnesium will correct the calcium deficiency.

• If a patient is known to have or suspected of having a pH abnormality, a concurrent pH test with ionized calcium level should be requested.

• Many drugs may cause increased or decreased levels of calcium. Calcium supplements taken shortly before specimen collection will cause falsely high values.

• Elevated serum protein increases calcium; decreased protein decreases calcium.

Pre analytical errors:

• Collection of blood samples

• Improper mixing of sample

• Fasting and non-fasting

Corrective action:

• Good mixing

• Propre collection of the sample

Post analytical errors:

• Test interpretation

• Test reporting

Reference Range:

Adult: 4.4 to 5.3 mg/dL

Child: 4.4 to 6.0 mg/dL