Serum Calcium

Calcium (Ca, Ca⁺⁺) is the most abundant cation in the body and participates in virtually all vital processes. About half the total amount of calcium circulates as free ions that participate in blood coagulation, neuromuscular conduction, intracellular regulation, glandular secretion, and control of skeletal and cardiac muscle contractility. The remaining calcium is bound to circulating proteins and plays no physiological role. Serum calcium measurement includes both ionized and protein-bound calcium.

Calcium ions undergo continuous turnover, with bone serving as the major reservoir. Serum contains only a small amount at any one time, but the serum level reflects overall calcium metabolism. Calcium levels are largely regulated by the parathyroid glands and vitamin D. Other substances affecting calcium levels include estrogens and androgens, calcitonin, and ingested carbohydrates. Increased or decreased serum proteins also may affect levels of protein-bound calcium.⁶²

Table 5-27 shows the various disorders and drugs associated with altered calcium levels. Abnormal serum calcium may produce cardiac dysrhythmias. Furthermore, serum calcium levels have a reciprocal relationship with serum phosphate levels; if one rises, the other tends to fall.

Reference Values ⬆ ⬇

	Conventional Units	SI Units
Newborns	7.0-11.5 mg/dL 3.7-7.0 mEq/L	1.75-2.90 mmol/L
Infants	8.6-11.2 mg/dL 5.0-6.0 mEq/L	2.15-2.80 mmol/L
Children	<12.0 mg/dL <6.0 mEq/L	<3 mmol/L
Adults	9-11 mg/dL 4.5-5.5 mEq/L	2.25-2.75 mmol/L
Critical values	<6 mg/dL or >13 mg/dL	<1.5 mmol/L or >3.25 mmol/L

Interfering Factors ⬆ ⬇

Values are higher in children because of growth and active bone formation.
Numerous drugs may alter serum calcium levels (see Table 5-27).
Increased or decreased serum protein levels may alter results.

Indications ⬆ ⬇

Evaluation of the effects of various disorders on overall calcium metabolism, especially diseases involving bone (see Table 5-27)
Detection of parathyroid gland loss after thyroid or other neck surgery, as indicated by decreased levels
Monitoring of the effects of renal failure on calcium levels, which are usually decreased in the disorder
Evaluation of cardiac dysrhythmias to determine whether altered serum calcium level is contributing to the problem
Evaluation of coagulation disorders to determine whether altered serum calcium level is contributing to the problem
Monitoring for the effects of various drugs on serum calcium levels (see Table 5-27)
Evaluation of the effectiveness of treatment for abnormal calcium levels, especially in deficiency states

Care Before Procedure ⬆ ⬇

Nursing Alert

Because altered serum calcium levels may produce cardiac dysrhythmias, abnormal values should be reported to the physician immediately so that treatment may be instituted.

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

Because many drugs may alter serum calcium levels, a medication history should be obtained. It is recommended that drugs that may alter test results be withheld for 12 to 24 hours before the test, although this practice should be confirmed with the person ordering the study.

Procedure ⬆ ⬇

A venipuncture is performed and the sample collected in a red-topped tube. The sample should be handled gently to avoid hemolysis and transported promptly to the laboratory.

Care After Procedure ⬆

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

Resume any medications withheld before the test.
Increased levels: Note and report increased levels. Assess for symptoms associated with hypercalcemia such as muscle relaxation, bone pain, nausea and vomiting, or increased intake of dietary calcium. Encourage fluid intake. Instruct client to restrict foods and medications high in calcium (milk and other dairy foods, eggs, some antacids).
Decreased levels: Note and report decreased levels. Assess for symptoms associated with hypocalcemia such as muscular irritability (tingling in fingers and around mouth, muscle cramping or twitching, facial spasm or Chvostek's sign, carpopedal spasm or Trousseau's sign, and tetany). Instruct client to eat foods and fluids high in calcium. Administer oral calcium supplement or replacement; prepare for IV calcium replacement in more severe cases.
Critical values: Notify the physician at once of levels less than 6 mg/dL or greater than 13 mg/dL.