- Red top (preferred) or green top tube
- 3-5 mL of whole blood
Additional information on specimen collection:
- Following collection, the specimen must be kept anaerobic
- Venous blood should be collected with tourniquet in place
- Serial samples should be collected at the same time of the day for comparison as calcium shows diurnal variation
- Do not use citrate, EDTA or oxalate as the anticoagulant. They may bind to calcium leading to low ionized calcium levels.
- Keep the specimen tightly capped
- Transport in an ice slurry
- Specimen should be analyzed promptly
- Sample pH must be determined simultaneously
Hypocalcemia (low Calcium) can clinically present with:
- Cardiac arrhythmias
- Changes in ECG
- Prolonged ST segment
- Prolonged Q-T interval
- Facial spasms (positive Chvostek's sign)
- Muscle cramps
- Muscle twitching (positive Trousseau's sign)
- Numbness in the extremities
- Seizures
- Tetany
- Tingling sensation
Hypercalcemia (high Calcium) can clinically present with:
The ionized calcium level measurement helps to:
- Detect neoplasms that produce ectopic parathyroid hormone
- Detect loss of parathyroid gland function after thyroid or other neck surgery (indicated by decreased levels)
- Detect hyperparathyroidism
- Evaluating cardiac arrhythmias and coagulation disorders (to check if an altered serum calcium level is a contributing factor)
- Evaluating disorders of calcium metabolism
- Evaluate the effect of protein on calcium levels
- Identify individuals with toxic levels of vitamin D
- Monitor ionized calcium during open-heart surgeries, liver transplantations, and other operations in which large volumes of blood anticoagulated with citrate are given
- Monitor therapy to correct abnormal calcium levels
- Monitor effects of drugs that alter calcium levels
- Monitor patients with:
- Secondary Hyperparathyroidism
- Sepsis
- Magnesium deficiency
- Renal failure
- Renal transplant
- Endocrine disorders
- Malignancies
- Cardiac disease
- Skeletal disorders
Additional information:
- Calcium circulating in the blood is found as:
- Free ionized form (47%)
- Bound to organic anions such as lactate, phosphate or citrate (10%)
- Bound to proteins (43%) with albumin making up 80% of this and globulin 20%
- Calcium free ions participate in vital body processes such as:
- Blood coagulation
- Control of skeletal and cardiac muscle contractility
- Glandular secretion
- Intracellular regulation
- Neuromuscular conduction
- Calcium levels are inversely proportional to phosphorus levels
- Ionized calcium levels are not affected by the protein concentrations or by disturbances in the metabolic acid-base balance. Elevations may be seen even if the total calcium is normal.
- Women have greater circadian variations in ionized calcium than men
- Related laboratory tests include:
- Albumin
- Alkaline phosphatase
- Calcitonin
- Calcium (blood and urine)
- Electrolytes
- Kidney stone panel
- Magnesium (blood and urine)
- Parathyroid hormone
- Phosphorus (blood and urine)
- Total protein
- Urinalysis
- Vitamin D
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below. Values listed are for blood pH=7.4.
| Conv. Units
(mg/dL) | SI Units
(mmol/L) |
|---|
| Adult | 4.5-5.4 | 1.13-1.35 |
| Child | 4.5-6.0 | 1.13-1.50 |
| Newborn | 4.4-5.5 | 1.10-1.38 |
| Critical low | <3.0 | <0.75 |
| Critical high | >6.5 | >1.63 |
Elevated ionized calcium level is seen in the following conditions:
- Ectopic PTH-producing tumor
- Hyperparathyroidism
- Malignancies
- Metastatic bone tumor
- Milk-alkali syndrome
- Multiple myeloma
- Paget's disease
- Physiological:
- Acidosis
- Exercise
- In neonates
- Meals high in calcium
- Tourniquet use
- Upright posture
- Sarcoidosis
- Substances and drugs:
- Androgens
- Antacids (some)
- Calcitriol
- Calcium carbonate
- Chlorthalidone
- DES
- Dihydrotachysterol
- Hydralazine
- Lithium
- Thiazide diuretics
- Thyroxine
- Vitamin D
- Tuberculosis
- Tumors producing PTH like substances
- Vitamin D excess
Decreased ionized calcium level is seen in the following conditions:
- Alkalosis
- Blood transfusions (large volume) with acid citrate dextrose containing blood as this chelates calcium in the blood
- Burns
- Drugs:
- Calcitonin
- Carbamazepine
- Citrates
- Estrogens
- Fluorides
- Foscarnet
- Furosemide
- Glucocorticoids
- Laxative abuse
- Octreotide
- Pamidronate
- Phenytoin
- Tetracycline
- Hyperventilation
- Hypoparathyroidism (primary)
- Magnesium deficiency
- Malabsorption
- Multiple organ failure
- Osteomalacia
- Pancreatitis
- Post-dialysis period (with low-calcium dialysate)
- Post-surgical period
- Pseudohypoparathyroidism
- Renal Failure
- Rickets
- Sepsis
- Toxic shock syndrome
- Trauma
- Vitamin D deficiency