Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

CACRU
89604
CACU
89777
Calcium/Creatinine Ratio, Random, Urine
Clinical Information: Calcium is the fifth most common element in the body. It is a fundamental
element necessary to form electrical gradients across membranes, an essential cofactor for many
enzymes, and 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 1,25 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, highly urinary calcium/creatinine ratios were found
in most hyperparathyroid patients, and less frequently in patients with hypercalcemia due to other
causes. Calcium/creatinine ratio of random urine specimens may be used to detect hypercalciuria in
patients suspected of having metabolic bone disease or other abnormalities of calcium metabolism.
Useful For: Identification of abnormal physiologic states causing excess or suppressed excretion of
calcium, such as hyperparathyroidism, vitamin D abnormality, diseases that destroy bone, prostate
cancer, and drug treatment, such as thiazide therapy.
Interpretation: Increased urinary excretion of calcium accompanies hyperparathyroidism, vitamin D
intoxication, diseases that destroy bone (such as multiple myeloma), metastasis from prostatic cancer,
and following calcium supplementation. Patients with absorptive hypercalciuria (increased gut
absorption) will have lowered urine calcium with dietary restriction and, therefore, can be differentiated
from patients with hypercalciuria caused by hyperparathyroidism, hyperthyroidism, Paget's disease, or
"renal leak" type of calciuria as seen in renal tubular acidosis. Thiazide drugs tend to reduce excretion
of calcium. For individuals consuming an average daily intake of 600 mg to 800 mg of calcium per day,
the normal daily excretion of calcium is: -Males: 25 mg to 300 mg -Females: 20 mg to 275 mg The
normal urine calcium/creatinine ratio is