- It is done on the serum of the patient.
- The blood should be collected without much pressure on the arm.
- Avoid prolonged tourniquet.
- EDTA cannot be used as the anticoagulant for the plasma.
- Obtain blood with minimal venous occlusion and without exercise or after restoring circulation.
- The serum is stable for 8 hours at 22 to 25 °C. But can keep at 4 °C for a longer period.
- Fasting specimen is preferred.
- 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 level.
- 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.
Purpose of serum calcium (Indications)
- Serum level of calcium is used to evaluate parathyroid function and metabolism.
- Serum calcium level is used to monitor renal failure and renal transplantation.
- Serum calcium level is used to evaluate hyperparathyroidism.
- Serum calcium level may be done in malignancies like multiple myeloma.
- Serum calcium level may be done to monitor calcium level before and after blood transfusions.
Pathophysiology of Calcium
- There is a large amount of calcium in the body and mainly in the bones and teeth.
- Normally the level of calcium in the blood is carefully controlled. When blood calcium levels get low Hypocalcemia, the bones release calcium to bring it back to a good blood level.
- When blood calcium levels get high Hypercalcemia, the extra calcium is stored in the bones or passed out of the body in stool and urine.
- The calcium is also needed to maintain metabolic process like as muscle contraction, transmission of neural impulses, clotting of the blood, cardiac function and inhibit cell destruction,
- Daily intake of about 400 mg is needed by the body.
- Body serum calcium levels are maintained by a balance between parathyroid Hormone PTH (Parathyroid gland hormone) and calcitonin (produced by C or parafollicular cells of thyroid).
- PTH increases the serum calcium level by increasing bone resorption and mobilizing Calcium.
- PTH indirectly increases the absorption of calcium from the gastrointestinal tract by the production of the vit. D.
Calcium metabolism and control
- PTH also increases the excretion of phosphate in the urine.
- Calcitonin decreases serum calcium and phosphate levels by inhibiting bone resorption.
- Decrease calcium level increases PTH which acts on the reservoir of calcium and lead to its release in the circulation.
- Half of the calcium in blood circulation is free in ionized form and half is in the protein-bound form mostly with albumin.
- 50% free or ionized (active) form.
- 40% is bound to protein.
- 10% is complexed with anions.
- In a patient with low serum albumin will have low serum calcium.
- So serum albumin level may be estimated with serum calcium level. Serum calcium level decreases 0.8 mg with every decrease of 1 gram albumin.
- Some physician prefers ionized serum calcium level to avoid the effect of albumin level.
- To label hypercalcemia, one should have three separate raised level of calcium.
- Symptoms of hypercalcemia are:
- Ultimately coma.
- The ectopic PTH-like hormone may be secreted by the tumors of lung, breast, and kidney.
- Symptoms of hypocalcemia shows:
A normal level of total serum Calcium
- Infant to one month = 7.0 to 11.5 mg/dL.
- One month to one year = 8.6 to 10.2 mg/ dL.
- Adult = 9 to 10.5 mg/dL.
- Its low level may lead to tetany.
||8.2 to 11.2
||6.2 to 11.0
|0 to 10 days
||7.6 to 10.4
|10 days to 2 years
||9.0 to 11.0
|2 years to 12 years
||8.8 to 10.8
|12 to 18 years
||8.4 to 10.2
|18 to 60 years
||8.6 to 10 .0
|60 to 90 years
||8.8 to 10.2
||8.2 to 9.6
- The conversion factor is x 0.25 for SI unit mmol/L
Hypercalcemia may be seen in the following conditions (plasma level >10.5 mg/dL):
- Metastatic bone tumor of lung, breast, and kidney.
- Milk-alkali syndrome.
- Multiple myelomas.
- Paget’s disease.
- Tumors producing a PTH-like substance.
- Vitamin D intoxication.
- Excessive calcium intake.
- Prolonged immobilization.
- Thiazide diuretics.
- Withdrawal of steroids.
- The majority (80 to 90 %) of the hypercalcemia cases are due to hyperparathyroidism or malignancy.
Hypocalcemia may be seen in the following conditions (plasma level <8.5 mg/dL):
- Pseudohypoparathyroidism due to lack of response to PTH.
- Malabsorption (inadequate absorption of nutrients from the intestinal tract).
- Renal failure (chronic).
- Rickets and vitamin D deficiency
- Liver disease (decreased albumin production).
- The most common cause of hypocalcemia is Hypoalbuminemia in which the ionized fraction may be normal while the total calcium level is decreased due to the low percentage of calcium bound to albumin.
- Correction formula is needed as follows:
- Corrected calcium level = measured calcium -- albumin g/dL + 4
- Acute hypo or hypercalcemia can be life-threatening.
Tabulated differential diagnosis of Hypercalcemia (Raised Calcium)
| Etiological causes
||due to post- renal transplant
An antacid containing calcium
||In most of the malignant tumors
Renal cell carcinoma
Liver cell carcinoma
Islet cell tumor
Natural foods good source of calcium:
||Amount of calcium
|| one cup
||8 whole figs
| White Beans
||1/2 cup dry roasted
- > 14 mg/dL Hypercalcemia leads to come and cardiac arrest.
- < 4 mg/dL Hypocalcemia leads to tetany.
Possible References Used
Back to tests