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Reflects intake, rates of intestinal calcium absorption, bone resorption and renal loss. Those processes relate to parathyroid hormone and vitamin D levels. Evaluation of bone disease, calcium metabolism, renal stones (nephrolithiasis);1 idiopathic hypercalciuria,2 and especially, parathyroid disorders. Follow-up of patients on calcium therapy for osteopenia.
High in 30% to 80% of instances of primary hyperparathyroidism, but urinary calcium excretion does not consistently, reliably distinguish hyperparathyroidism from other entities. High in sarcoidosis.3 Increased with immobilization, with steroid therapy, with Paget disease, and in primary (idiopathic) hypercalciuria.4 Increased with entities causing high ultrafiltrable calcium: ectopic hyperparathyroidism, some cases of renal tubular acidosis, Fanconi syndrome, increased calcium intake, vitamin D intoxication, hyperthyroidism, diabetes mellitus, acromegaly, glucocorticoid excess, some cases of Crohn's disease and ulcerative colitis, myeloma, some instances of leukemia and lymphoma, and carcinoma metastatic to bone. Reported relationship to hematuria in children.5
Low in familial hypocalciuric hypercalcemia, for which urine calcium measurements are mandatory; low with thiazide diuretics, vitamin D deficiency, renal osteodystrophy, vitamin D resistant rickets, hypoparathyroidism, pseudohypoparathyroidism and preëclampsia.6
Decreased in patients on oral contraceptives. Lacks specificity for hyperparathyroidism when increased. Five percent of the population have hypercalciuria.4
Twenty percent to 25% patients who form calcium stones have hyperuricosuria. Urinary calcium reflects in part the relation between GFR and tubular reabsorption.
25 mL aliquot
Preferred: Plastic urine container with at least 10 mL 6N HCl (hydrochloric acid). Specimens submitted without preservatives should be acidified after receipt to a pH <2.0 to dissolve calcium salts.
Urinary calcium results are more meaningful if the patient has been on a low calcium, neutral ash diet for three days prior to urine collection. Drugs affecting mineral metabolism should be withdrawn, if possible, two to four weeks prior to and during collection. These include antacids, phosphates, diuretics, glucocorticoids, carbonic anhydrase inhibitors, and anticonvulsants.
Instruct the patient to void at 8 AM and discard the specimen. Then collect all urine including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM the next morning). Screw the lid on securely. Transport the specimen promptly to the laboratory. Container must be labeled with patient's full name, room number, date and time collection started, and date and time collection finished. pH must be <2.
Maintain specimen at room temperature.
Causes for Rejection
The test request form must state date and time collection started and date and time collection finished. State total volume.
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|003269||Calcium, 24Hr Urine||013490||Calcium, Urine||mg/dL||18488-7|
|003269||Calcium, 24Hr Urine||013243||Calcium, Urine 24hr||mg/24 hr||6874-2|