Definition: calcium is present in 3 different forms in the plasma: ionized, bound and complex.
Only ionized calcium is physiologically significant. The percentage of ionized calcium is affected by pH, phosphorus, and albumin levels.
The relationship between ionized calcium and plasma pH is reciprocal (the increase in pH decreases the percentage of Ca ++ ionization).
Patients with Alkalosis, for example, may show signs of hypocalcemia despite an average level of total calcium.
Changes in albumin will affect total serum calcium without changing the free calcium level.
Signs and symptoms of calcium alterations in the blood
- Numbness with tingling of the fingers, extremities, and the region of the surgery
- Hyperactive reflexes
- Muscle pains
- Carpopedales spasms
Cardiac effects include decreased myocardial contractility and heart failure.
History and risk factors
1) Decreased ionized calcium: Alkalosis; Administration of large amounts of citrated blood (can bind calcium); Hemodilution (volume replacement, etc.)
2) Increase in calcium loss in body fluids: certain diuretics.
3) Decreased intestinal absorption: decreased intake; Alteration of vitamin D metabolism (renal failure); Chronic diarrhea, post-gastrectomy.
4) Hypoparathyroidism: congenital or acquired.
5) Hyperphosphatemia: renal failure. When hypocalcemia persists, it is best to delay the administration of calcium supplements until the serum phosphate level is less than 6 mg / dL to reduce the risk of metastatic calcification.
6) Hypomagnesemia (decreased action and release of PTH). Chronic alcoholism; acute pancreatitis. Hypocalcemia is difficult to correct without first normalizing the serum magnesium concentration.
The total serum calcium may be less than 8.5 mg / dL. Serum calcium levels should be evaluated with serum albumin. For each drop of 1.0 mg / dL in the blood albumin, there is a drop of 0.8 – 1.0 mg / dL in the total calcium level.
The ionized calcium will be less than 4.2 mg / dL. Symptoms of hypocalcemia usually occur when ionized levels fall to <2.5 mg / dL.
- Parathyroid hormone: decreased levels occur in hypoparathyroidism.
- Magnesium and phosphorus levels: can be verified to identify possible causes of hypocalcemia.
The treatment of Alkalosis should be based on:
- Present symptoms: Paresthesias, tetany, carpopedal spasm, seizures
- Signs: Chvostek or Trousseau signs, alteration of cardiac contractility, prolongation of the QT interval, bradycardia).
- The absolute level of calcium.
- Decrease rate (for example, acute decrease versus chronic decrease).
The therapeutic approach and the treatment of hypocalcemia depend significantly on the severity of the symptoms and the underlying cause. In patients with asymptomatic hypocalcemia, it is essential to check with repeated measures (ionized or corrected total calcium for serum albumin).
The first step in evaluating a patient with hypocalcemia is to verify with a repeated measurement (total serum calcium corrected for albumin or ionized calcium) that there is an actual decrease in serum calcium concentration.
If available, previous serum calcium values should also be reviewed. If the patient has low serum calcium or ionized calcium concentration corrected with albumin, an additional evaluation will be indicated to identify the cause.
Hypoalbuminemia: Correction of calcium – Calcium in serum binds proteins, mainly albumin. As a result, the total serum calcium concentration in patients with low or high serum albumin levels may not accurately reflect the ionized (or free) physiologically essential calcium concentration.
Each reduction of 1 g / dL in serum albumin concentration will decrease the total calcium concentration by approximately 0.8 mg / dL (0.2 mmol / L) without affecting the concentration of ionized calcium and, therefore, without producing any symptoms or signs of hypocalcemia.
A blood calcium test is ordered to detect, diagnose, and control conditions related to bones, heart, nerves, kidneys, and teeth.
The test can also be ordered if a person has symptoms of a parathyroid disorder, malabsorption, or an overactive thyroid.
A total calcium level is often measured as a routine health examination. Included in the full metabolic panel (PMC) and the basic metabolic panel (PMB), these tests are done together to diagnose or monitor a variety of conditions.
When an abnormal result of total calcium is obtained, it is considered an indicator of an underlying problem. To help diagnose the underlying problem, additional tests are often done to measure ionized calcium, urine calcium, phosphorus, magnesium, vitamin D, parathyroid hormone, and the peptide related to parathyroid hormone.
Parathyroid hormone and vitamin D are responsible for maintaining blood calcium concentrations within a narrow range of values. If calcium is abnormal, measuring calcium and parathyroid hormone together can help determine if the parathyroid glands usually function.
Measuring calcium in the urine can help determine if the kidneys are excreting the proper amount of calcium. Testing for vitamin D, phosphorus, and magnesium can help determine if there are other deficiencies or excesses.
Frequently, the balance between these different substances (and changes in them) is as essential as the concentrations.
Calcium can be used as a diagnostic test if a person has symptoms that suggest:
- Kidney stones
- Bone disease
- Neurological disorders.
The total calcium test is the most frequently ordered test to assess the calcium status. In most cases, it is a good reflection of the amount of free calcium present in the blood since the balance between free and bound is generally stable and predictable.
However, the balance between free and free calcium is altered in some people, and total calcium is not a good reflection of calcium status. Under these circumstances, measurement of ionized calcium may be necessary.
Some conditions in which ionized calcium should be the test of choice are critically ill patients, those who receive blood transfusions or intravenous fluids, patients undergoing major surgery, and people with abnormalities in blood protein such as low albumin.
Large fluctuations in ionized calcium can cause the heart to slow down or pump too fast; it can cause the muscles to go into spasm and cause confusion or even coma.