Calcium ionized (Ca), Free Calcium Part 2
- Collect blood anaerobically and draw without pressure or stasis.
- The sample is stable for 6 hours at 4 °C.
- Plasma or serum can be stored for a longer period at -20 °C.
- The nonfasting sample is acceptable.
- The prolonged tourniquet should be avoided because it will lower pH and increase the calcium.
Purpose of the test (Indication):
- This test is used to determine physiologically active or free Calcium in patients with altered proteins e.g in chronic renal failure, nephrotic syndrome, malabsorption, and multiple myeloma.
- Ionized calcium value reflect calcium metabolism better than total calcium.
- A significant decrease in ionized calcium regardless of total calcium may lead to an increase in neuromuscular irritability and tetany.
- This is also advised in the parathyroid diseases.
- Fasting specimen is preferred.
- Serum pH can affect the calcium level. A decreased pH can cause an increased level of calcium.
- Venous stasis or erect posture increased the calcium level by 0.6 mg/dL.
- There is diurnal variation, higher in PM than AM.
- Separate immediately from RBCs to avoid uptake of calcium by these cells (RBCs).
- Excessive intake of milk leads to increased calcium levels.
- Vitamin D intoxication also increases the calcium level.
- Check the albumin level because hypoalbuminemia leads to an artificial decrease in the calcium level.
- Drugs may increase the serum calcium level like calcium salts, alkaline antacids, thiazide diuretics, vitamin D, parathyroid and thyroid hormones, and androgens.
- Drugs may decrease the calcium level like aspirin, anticonvulsant, heparin, laxatives, diuretics, magnesium salts, and oral contraceptives.
- This is the calcium not bound to protein.
- 99% of the calcium is present in the bone structure.
- Calcium in plasma is:
- 50% free or ionized and is the active form.
- 40% is bound to protein.
- 10% is complexed with anions.
- Ionized calcium or free calcium in order to exert its physiological effects upon:
- The neuromuscular junction.
- Bone deposition.
- The most valuable clinical information is provided by a knowledge of the concentration of Ca++ rather than of total Ca++.
- Functions of the calcium:
- All body cells need calcium.
- Calcium is needed for strong muscles and bones.
- This is also important for the normal function of the heart.
- Calcium is needed for the nerve signals.
- Calcium helps in the contraction of muscles.
- Calcium is needed for the blood clotting mechanism.
- Calcium maintains plasma membrane potential.
- This is a cofactor in the enzymatic reaction.
Normal Ionized Calcium:
- Ionized calcium
- Whole blood adult = 4.65 to 5.28 mg/dL (1.175 to 1.375 mmol/L)
- Newborn = 4.20 to 5.58 mg/dL.
- The ratio of ionized Ca++ to total Ca++ = 48 to 56%.
- Newborn = 4.20 to 5.58 mg/dL (1.05 to 1.37 mmol/L).
- 2 months to 18 years = 4.80 to 5.52 mg/dL (1.20 to 1.38 mmol/L).
- Adult = 4.5 to 5.6 mg/dL (1.05 to 1.3 mmol/L).
|Age||Whole blood mg/dL||Serum mg/dL||Capillary blood mg/dL|
|Cord blood||5.20 to 6.40|
|2 hours||4.84 to 5.84|
|24 hours||4.40 to 5.44||4.20 to 5.48|
|3 days||4.60 to 5.68||4.40 to 5.68|
|5 days||4.88 to 5.92||4.80 to 5.92|
|Youth||4.80 to 5.52|
|Adults||4.64 to 5.28|
|18 to 60 years||4.60 to 5.08|
|60 to 90 years||4.64 to 5.16|
|>90 years||4.48 to 5.28|
- To convert into SI unit multiplying factor is x 0.25 = mmol/L
The increased level is seen in:
- Primary hyperparathyroidism.
- PTH-producing tumors.
- Various malignancies.
- Excess intake of vit.D.
The decreased level is seen in:
- primary hypoparathyroidism.
- Vitamin D deficiency.
- After blood transfusion.
- After major surgery.
- Trauma, burns, and sepsis.
- After hemodialysis.
- Multiple organ failures.
- Please see more details on the Calcium level (total).
Natural foods a good source of calcium:
|Food||Quantity||Amount of calcium|
|Kale||one cup||245 mg|
|Milk||one cup||305 mg|
|Yogurt||6 oz||300 mg|
|Cheese||one oz||224 mg|
|Dried figs||8 whole figs||107 mg|
|White Beans||one cup||191 mg|
|Turnip greens||one cup||195 mg|
|Black-eyed beans||1/2 cup||185 mg|
|Canned salmon||1/2 cup||232 mg|
|Orange juice||one cup||500 mg|
|Orange||one medium||65 mg|
|Sesame seed||one teaspoon||88 mg|
|Almond||1/2 cup dry roasted||72 mg|
|Instant oatmeal||one cup||187 mg|
|Soy milk||one cup||300 mg|
|Firm Tofu||1/2 cup||861 mg|
|Broccoli||one cup||62 mg|