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

CAU
8594
apparent idiopathic hypoparathyroidism should be considered for CASR mutation screening. The
correct diagnosis is important, as ADH patients are more susceptible to the side effects of
1,25-dihydroxy vitamin D therapy than other patients with hypoparathyroidism and because of genetic
counseling considerations. CASR mutation screening, as described above, can assist in reaching a
definite diagnosis. Patients with Bartter's syndrome who have hypocalcemia and inappropriately low
serum PTH levels that do not change after repletion of magnesium stores, might be suffering from
Bartter's syndrome type V, which is caused by extreme gain of function mutations of the CASR.
Identification of the known Bartter's type V associated L125P mutation confirms the diagnosis, while
identification of other ADH-causing mutations or novel alteration(s) increase the likelihood of CASR
mutation-related Bartter's syndrome, but do not confirm it without additional family or functional
studies. Absence of any mutations or the presence of polymorphism(s) that are known to be functionally
neutral makes the diagnosis very unlikely (see Cautions for exceptions). See Parathyroid Disease and
the Calcium-Sensing Receptor Gene (November 2005 Communique') in publications for additional
information.
Reference Values:
An interpretive report will be provided.
Clinical References: 1. Hendy GN, D'Souza-Li L, Yang B, et al: Mutations of the calcium-sensing
receptor (CASR) in familial hypocalciuric hypercalcemia, neonatal severe hypocalciuric
hyperparathyroidism, and autosomal dominant hypocalcemia. Hum Mutat 2000 Oct;16(4):281-296. The
authors maintain a CASR polymorphism/mutation database: http://www.casrdb.mcgill.ca/ 2. Lienhardt A,
Bai M, Lgarde JP, et al: Activating mutations of the calcium-sensing receptor: management of
hypocalcemia. J Clin Endocrinol Metab 2001 Nov;86(1):5313-5323 3. Hu J, Spiegel AM: Naturally
occurring mutations of the extracellular Ca2+ -sensing receptor: implications for its structure and
function. Trends Endocrinol Metab 2003 Aug;14(6):282-288 4. Naesens M, Steels P, Verberckmoes R, et
al: Bartter's and Gitelman's syndromes: from gene to clinic. Nephron Physiol 2004;96(3):65-78 5. Egbuna
OI, Brown EM: Hypercalcaemic and hypocalcaemic conditions due to calcium-sensing receptor
mutations. Best Pract Res Clin Rheumatol 2008; 22:129-148
Calcium, 24 Hour, 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 is excreted in both urine and feces.
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: -25 mg to 300 mg for men -20 mg to 275 mg for women
Reference Values:
Males: 25-300 mg/specimen*
Females: 20-275 mg/specimen*
Hypercalciuria: >350 mg/specimen
*Values are for persons with average calcium intake (ie, 600-800 mg/day).
Clinical References: Rockwell GF, Morgan MJ, Braden G, et al: Preliminary observations of
urinary calcium and osteopontin excretion in premature infants, term infants and adults. Neonatology
Current as of January 3, 2013 2:22 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 352