Calcium is the fifth most common element in the body. It is a fundamental element necessary to form electrical gradients across membranes, is an essential cofactor for many enzymes, and is the main constituent in bone. Under normal physiologic conditions, the concentration of calcium in serum and in cells is tightly controlled. Calcium exists in 3 states in the body; bound to protein, bound to small anions, and in the free (ionized) state. The concentration of serum calcium in the ionized state is regulated by parathyroid hormone (PTH) and 1,23 dihydroxy vitamin D.
Circulating calcium is excreted by glomerular filtration and reabsorbed in the proximal tubules. Calcium reabsorption in the proximal tubule is affected by tubular sodium concentration, whereas PTH induces calcium uptake in the distal tubule and the collecting duct. Excess is excreted in the urine and the feces.
Because PTH increases renal tubular reabsorption of calcium, one would expect patients with hyperparathyroidism to be hypocalciuric. However, high urinary calcium/creatinine ratios were found in most hyperparathyroid patients, and less frequently in patients with hypercalcemia due to other causes.
Sample Report
Test Code(s):
003324, 1635
Preparation:
You must take your lab order to the lab to obtain a proper specimen container before collection. Medications affecting mineral metabolism should be withdrawn, if possible, two to four weeks prior to and during collection. Check with physician before stopping any medications. Urinate at 8am and discard the specimen. Then collect all urine in 24-hour period, ending with final collection at 8am the next morning. Refrigerate the collected urine between all voidings or keep it in a cool place. Screw the lid on securely. Transport the specimen promptly to the laboratory. Container must be labeled with full name, date and time collection started, and date and time collection finished.
Test Results:
2-4 Business days. May take longer based on weather, holiday or lab delays.
