Calcium ionized (Ca), Free Calcium Part 2

Sample

1. Collect blood anaerobically and draw without pressure or stasis.
2. The sample is stable for 6 hours at 4 °C.
3. Plasma or serum can be stored for a longer period at -20 °C.
4. The nonfasting sample is acceptable.
   1. The prolonged tourniquet should be avoided because it will lower pH and increase the calcium.

Purpose of the test (Indication):

1. 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.
2. Ionized calcium value reflect calcium metabolism better than total calcium.
3. A significant decrease in ionized calcium regardless of total calcium may lead to an increase in neuromuscular irritability and tetany.
4. This is also advised in the parathyroid diseases.

Precautions:

1. Fasting specimen is preferred.
2. Serum pH can affect the calcium level. A decreased pH can cause an increased level of calcium.
3. Venous stasis or erect posture increased the calcium level by 0.6 mg/dL.
4. There is diurnal variation, higher in PM than AM.
5. Separate immediately from RBCs to avoid uptake of calcium by these cells (RBCs).
6. Excessive intake of milk leads to increased calcium levels.
7. Vitamin D intoxication also increases the calcium level.
8. Check the albumin level because hypoalbuminemia leads to an artificial decrease in the calcium level.
9. Drugs may increase the serum calcium level like calcium salts, alkaline antacids, thiazide diuretics, vitamin D, parathyroid and thyroid hormones, and androgens.
10. Drugs may decrease the calcium level like aspirin, anticonvulsant, heparin, laxatives, diuretics, magnesium salts, and oral contraceptives.

Pathophysiology:

1. This is the calcium not bound to protein.
2. 99% of the calcium is present in the bone structure.
3. Calcium in plasma is:
   1. 50% free or ionized and is the active form.
   2. 40% is bound to protein.
   3. 10% is complexed with anions.
4. Ionized calcium or free calcium in order to exert its physiological effects upon:
   1. The neuromuscular junction.
   2. Membranes.
   3. Bone deposition.
      1. The most valuable clinical information is provided by a knowledge of the concentration of Ca⁺⁺ rather than of total Ca⁺⁺.

5. Functions of the calcium:
   1. All body cells need calcium.
   2. Calcium is needed for strong muscles and bones.
   3. This is also important for the normal function of the heart.
   4. Calcium is needed for the nerve signals.
   5. Calcium helps in the contraction of muscles.
   6. Calcium is needed for the blood clotting mechanism.

4. 7. Calcium maintains plasma membrane potential.
   8. This is a cofactor in the enzymatic reaction.
      

      Calcium intracellular and Extracellular distribution

Normal Ionized Calcium:

Source 1

• 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%.

Source 2

• 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:

1. Primary hyperparathyroidism.
2. PTH-producing tumors.
3. Various malignancies.
4. Excess intake of vit.D.

The decreased level is seen in:

1. primary hypoparathyroidism.
2. Vitamin D deficiency.
3. After blood transfusion.
4. After major surgery.
5. Trauma, burns, and sepsis.
6. Pancreatitis.
7. After hemodialysis.
8. 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

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