Calcium

Excerpt

Calcium is a prominent molecule in the body involved in many biochemical processes. This mineral is essential for proper cardiac function, the structural integrity of bone, muscular contraction, and acts as an enzymatic signal in biochemical pathways. Calcium is tightly regulated by the parathyroid hormone (PTH), calcitonin, and calcitriol, which regulate serum calcium levels. Calcium must be ingested endogenously, and absorption in the gastrointestinal system is influenced by hormones PTH and calcitriol (1,25-dihydroxyvitamin D).

Serum calcium can be measured by a venous sample, with physiologic levels ranging from 8.8 mg/dL to 10.4 mg/dL for total calcium and 4.7 mg/dL to 5.2 mg/dL for ionized calcium. Total calcium values should be corrected for current albumin concentrations, which act as a carrier protein and can affect the reported results. Calcium can also be analyzed from urine by calcium concentration, urine calcium to creatinine ratio (UCa: UCr), or fractional excretion of calcium (FeCa). Calcium derangements can result from many diseases or therapies that affect hormone secretion, receptor sensitivities, intestinal absorption, and renal effectiveness. Laboratory error can cause inaccurately reported calcium levels, and preventive measures should be included in specimen collection and analysis.