What Is Serum Calcium?

Most of the calcium in the blood exists in the plasma, and the plasma calcium has two parts, non-diffusive calcium and diffusible calcium.

Serum calcium

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Most of the calcium in the blood is found in

Calcium is the most abundant cation in the body. The atomic formula is Ca and the atomic weight is 40.08. Normal adults contain 25-30 mol of calcium, more than 99% of which are in bones and teeth. Bone is the largest calcium storage in the body.

(1) Methyl thymol blue colorimetric method (MTB):

Serum calcium: 2.03 2.54mmol / L for adults

Children 2.25 2.27mmol / L (9 ~ 11mg / dl)

Serum ionized calcium: 1.13 1.35mmol / L

erythrocyte calcium: almost all of the calcium in the blood is in plasma, and there are only 15.72 mol / L hematocrit in red blood cells.

Urinary calcium excretion: It varies greatly with different diets:

A. <3.75mmol / 24h when on a low calcium diet;

B. <6.25mmol / 24h in general calcium diet;

C. High calcium diet can reach <10mmol / 24h.

Saliva calcium: 0.74 to 1.69 mmol / L.

(2) Direct colorimetric method of o-cresolphthalein complex ketone: see (MTB) method.

(3) Titration method of ethylenediamine tetraacetic acid disodium: see (MTB) method.

(4) Determination of ionized calcium: 1.10 to 1.34 mmol / L for serum ionized calcium in adults.

(1) Ethylenediamine tetraacetic acid disodium titration method:

Increased blood calcium:

A. Hyperparathyroidism: There are two kinds of primary and secondary. Secondary to rickets, osteomalacia, and chronic renal failure. The increase of blood calcium is greater than 2.6mmol / L, the highest can reach 4.5mmol / L, meanwhile the blood phosphorus decreases, less than 1.13mmol / L, the lowest can reach 0.64mmol / L. Urinary calcium increased, which was greater than 9.68 mmol / 24h in men and 8.07 mmol / 24h in women.

B. Vitamin D excess: Both serum calcium and phosphorus can increase, and calcium deposits in the kidney can develop into kidney calcification.

C. Multiple myeloma blood calcium increase: often due to increased globulin, increased with calcium.

D. Extensive bone metastases from tumors: Moderate increase in blood calcium, but normal or slightly higher phosphorus, increased excretion of calcium in urine, increased excretion of hydroxyproline in urine, reflecting the breakdown of bone collagen.

E. Addison's disease.

F. Sarcoidosis: Due to excessive absorption of calcium in the intestine, the blood calcium is increased, and the blood phosphorus is slightly higher.

Decreased blood calcium: Decreased blood calcium can cause increased neuromuscular stress and twitch hands and feet, which can be seen in the following diseases:

A. Hypoparathyroidism: Hypothyroidism caused by thyroid surgery and parathyroid glands, serum calcium can be reduced to 1.25 to 1.50mmol / L, serum phosphorus can be increased to 1.62 to 2.42mmol / L, pseudoparathyroidism Hypofunction is not a lack of parathyroid hormone, and the lack of adenylate cyclase in the kidney, which responds to parathyroid hormone, causes a decrease in serum calcium.

B. Chronic nephritis uremia: Insufficient vitamin D3-1 hydroxylase and inadequate active vitamin D3 in renal tubules cause total serum calcium to decrease. Binding calcium is reduced due to reduced plasma albumin, but ionizing calcium is caused by metabolic acidosis. Increased, so hand and foot convulsions are less likely to occur.

C. Rickets and osteochondrosis: Lack of vitamin D in the body makes calcium absorption disorder, and serum calcium and phosphorus are low.

D. Inadequate hypocalcemia: In severe celiac disease, calcium in the diet and non-absorbed fatty acids produce calcium soap and are excreted.

E. After a large amount of citrate anticoagulation: it can cause hypocalcemia in the hands and feet.

(2) Determination of ionized calcium:

The measurement of ionized calcium is the most important for larger surgical operations, such as cardiac surgery, transplantation, and other anticoagulant surgery that requires a large amount of citrate input, or postoperative sepsis, kidney, and heart failure patients. Or burn patients, because the serum protein levels have decreased in these states, acid-base imbalances and citrate blood products have been imported, repeated measurement of total calcium has no meaning. If calcium is to be supplemented, ionic calcium determination is the best guide for the correct treatment of these patients.

When hypocalcemia of the newborn is suspected, ionized calcium should be measured, and if complications continue to occur, it should be measured often.

Kidney disease After kidney transplantation or in patients undergoing hemodialysis, calcium metabolism is often changed and sometimes intense. Therefore, maintaining a slight blood calcium balance during hemodialysis is important for maintaining good heart function. The measurement of ionized calcium is the best way to monitor this. Nephrotic syndrome is characterized by a decrease in serum protein, and the levels of total calcium and ionized calcium decrease. Correcting total calcium at the protein level may cause overestimation of ionized calcium.

In patients with primary hyperparathyroidism, ionized calcium is elevated in more than 90% of cases, and total calcium is increased in approximately 80% of cases.

In patients with acute pancreatitis, ionized calcium decreases within 24 hours after onset, but returns to normal by 48 hours. Total calcium was also slightly reduced at 48h. At this time, because albumin was also reduced, a sustained decrease in ionic calcium was associated with severe pancreatitis.

The percentage of increase of ionized calcium in patients with malignant tumors is greater than the total calcium, which may also be used for screening tests of tumors. When the cause of hypercalcemia is difficult to determine, the presence of malignancies must be considered.