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Calcium levels can be measured with ionized calcium tests – Aug 2012

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A comparison of corrected serum calcium levels to ionized calcium levels in haemodialysis patients.

Ann Biol Clin (Paris). 2012 Mar-Apr;70(2):210-2.
Gouri A, Dekaken A.
Laboratoire de biochimie médicale, Hôpital Ibn-Zohr Guelma, Annaba, Algérie. pharmagor at gmail.com

Aberrations in calcium homeostasis are common observed in patients with chronic renal failure. Measure of total calcium does not reflect the real variation of the calcium status. The proper method to evaluate this issue in hemodialysis patients has not been completely defined. This study aimed to compare the corrected serum calcium levels to ionized calcium levels in hemodialysis patients. Thirty one patients on chronic haemodialysis admitted at the hemodialysis department were retrospectively reviewed. Calcium status was evaluated by measure of ionized levels and as a function of serum calcium levels corrected for albumin aberrations. Based on the measurement of ionized calcium and total calcium corrected, patients were classified into three categories: hypocalcemic, normocalcemic and hypercalcemic. Our result showed that the corrected serum calcium values failed to accurately classify calcium status in 41% of cases. The sensitivity and specificity of the corrected serum calcium formula to evaluate hypocalcemia were 53% and 85%, respectively. Corrected serum values underestimated the prevalence of hypocalcemia and overestimated the prevalence of normocalcemia. In total, the results obtained allow to conclude the lack of interest in the use of correction formulas. Calcium homeostasis should be evaluated by ionized calcium levels rather than as a function of serum calcium and albumin.

PMID: 22484533
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The Importance of Measuring ionized Calcium in Characterizing Calcium Status and Diagnosing Primary Hyperparathyroidism.

J Clin Endocrinol Metab. 2012 Jun 28.
Ong GS, Walsh JP, Stuckey BG, Brown SJ, Rossi E, Ng JL, Nguyen HH, Kent GN, Lim EM.
Department of Endocrinology and Diabetes (G.S.Y.O., J.P.W., B.G.A.S., S.J.B., J.L.N., E.M.L.), Keogh Institute for Medical Research (B.G.A.S.), and Department of Endocrine Surgery (H.H.N.), Sir Charles Gairdner Hospital, Nedlands 6009, Australia; Department of Clinical Biochemistry (G.S.Y.O, E.R., J.L.N., G.N.K., E.M.L.), PathWest Laboratory Medicine, Queen Elizabeth II Medical Centre, Nedlands 6009, Australia; and School of Medicine and Pharmacology (J.P.W., B.G.A.S.), The University of Western Australia, Crawley 6009, Australia.

Context:Serum total calcium (tCa) is routinely measured for diagnosing calcium disorders but may not reflect levels of biologically active ionized calcium (iCa) in disease or detect all cases of primary hyperparathyroidism.

Objective:We investigated the utility of measuring iCa and tCa for diagnosing primary hyperparathyroidism.Design:This was an observational, retrospective, cross-sectional study.

Patients:We studied a biochemistry cohort of consecutive ambulatory outpatients with suspected bone or calcium metabolism disorders referred for calcium metabolism biochemistry panels and a surgical cohort of consecutive tertiary hospital patients whose parathyroid specimens were submitted to a single center, and consecutive parathyroidectomy patients of a single surgeon with specimens submitted to a different center.

Results:In 5490 biochemistry cohort patients, discordance between iCa and tCa in classifying calcium status occurred in 12.6% of cases overall but was worse in hypercalcemic (whether defined by tCa and/or iCa) cases (49%) and hypocalcemic cases (92%). Reliance on tCa alone would miss 45% with ionized hypercalcemia. In 315 biochemistry cohort cases with PTH-dependent hypercalcemia, 130 (41%) had isolated ionized hypercalcemia at diagnosis. In 143 patients with histologically proven parathyroid disease, 24% had isolated ionized hypercalcemia at diagnosis. These patients were younger (P = 0.022) with milder ionized hypercalcemia and better renal function (both P ? 0.001) than patients presenting with concurrently elevated iCa and tCa.

Conclusion:In abnormal calcium states, tCa frequently disagrees with iCa in classifying calcium status. Histologically proven parathyroid disease can present with isolated ionized hypercalcemia. Measurement of iCa is required to accurately assess calcium status and improve diagnostic accuracy.

PMID: 22745247
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Investigation of hypercalcemia.

Clin Biochem. 2012 Aug;45(12):954-63. Epub 2012 May 5.
Endres DB.

Hypercalcemia is a relatively common clinical finding. Primary hyperparathyroidism, hypercalcemia associated with malignancy and chronic renal failure (with calcium and vitamin D metabolite treatment or tertiary hyperparathyroidism) are the most common causes. Less common causes of hypercalcemia include vitamin D-related (granulomatous diseases, lymphoma, vitamin D intoxication), other endocrine (thyrotoxicosis), medications (milk-alkali, thiazides, lithium) and other causes (immobilization, familial hypocalciuric hypercalcemia). The clinical laboratory is central to the diagnosis and differential diagnosis of hypercalcemia. Its role has expanded from measuring routine chemistry tests such as total calcium, phosphate, creatinine and alkaline phosphate to include quantification of ionized calcium, parathyroid hormone (PTH) and vitamin D metabolites. In spite of this progress, the diagnosis and differential diagnosis of hypercalcemia can be significantly improved by:
1) increasing the availability and utilization of ionized calcium since total and corrected calcium are often inaccurate;
2) establishing more accurate reference intervals for parathyroid hormone by excluding individuals who are vitamin D insufficient or deficient; and
3) harmonizing intact PTH immunoassays.

Copyright © 2012. Published by Elsevier Inc. PMID: 22569596
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