Assessment

Test

Abnormality with Normal Result Condition

Explanation

Serum calcium: total calcium, including free ionized calcium and calcium bound with protein or organic ions

Accumulation of calcium above normal levels in the extracellular fluid compartment; clinical manifestations generally occur when calcium levels are above 12 mg/dL and tend to be more severe if hypercalcemia develops rapidly; if ionized calcium cannot be measured, total serum calcium can be corrected by adding 0.8 mg/dL to the total calcium level for every 1 g/dL decrease of serum albumin below 4 g/dL; the corrected value determines whether true hypocalcemia is present. When calcium levels are reported as high or low, calculate the actual level of calcium by the following formula: Corrected total calcium (mg/dL) = (measured total calcium mg/dL) + 0.8 (4.4-measured albumin g/dL) (highlight box continues on page 460)

critical value:

460 Hyperparathyroidism

Diagnostic Highlights (continued)

Test

Normal Result

Abnormality with Condition

Explanation

Serum ionized calcium: unbound calcium; level unaffected by albumin level

4.5-5.1 mg/dL

>5.5 mg/dL

Ionized calcium is approximately 46%-50% of circulating calcium and is the form of calcium available for enzymatic reactions and neuromuscular function; levels increase and decrease with blood pH levels; for every 0.1 pH decrease, ionized calcium increases 1.5%-2.5%.

Serum parathyroid hormone level

1G-B5 pg/mL

Elevated In more than 90% of people with primary hyperparathyroidism

Determines presence of hyperpara-thyroidism

Other Tests: Supporting tests include x-rays, electrocardiogram (ECG), ultrasound, and magnetic resonance imaging (MRI).

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