Ion Selective Electrodes (ISEs) and interferences--a review.

Invited critical reviewIonized calcium

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...

The Importance of Measuring Ionized Calcium in Characterizing Calcium Status and Diagnosing Primary Hyperparathyroidism

Miniaturized whole blood biosensors, patient-focused hospitals, and rising expectations of patients and physicians are shifting laboratory diagnostics to the point of care. Expanding transplantation and intensive care are increasing the need for rapid test results. Whole blood analysis improves accuracy, eliminates centrifugation, reduces response time, and conserves blood volume. Several hand-held, and over 20 portable or transportable whole blood instruments are now available. Criteria for instrument evaluation include test menus, point-of-care features, analysis time, on-site performance, and information integration. Whole blood analyzers measure several vital indicators (pO2, pCO2, pH, hematocrit, K+, Ca2+, Na+, Cl−, glucose, and lactate) simultaneously in less than 2 min with less than 200 μl of whole blood. Other in vitro tests are available (Mg2*, osmolality, CO2 content, urea nitrogen, β-hydroxybutyrate, hemoglobin, coagulation) or under development (HCO3− phosphorus). Some can be monitore...

New Whole Blood Analyzers and Their Impact on Cardiac and Critical Care

Evaluation of Clinical and Clinical Chemical Parameters in Periparturient Cows

We report results for adjusted ionized calcium (at pH 7.4) and actual ionized calcium (at actual pH) in capillary blood from 183 patients with disorders of calcium metabolism (primary hyperparathyroidism, secondary hyperparathyroidism of malabsorption, primary hypoparathyroidism, Paget's disease, acromegaly, hypercalcemia of malignancy, osteoporosis, sarcoidosis, idiopathic hypercalciuria, and familial hypocalciuric hypercalcemia). The correlation and the equation for the linear regression between adjusted ionized calcium (y) and actual ionized calcium (x) were y = 1.011x + 0.005 mmol/L, r = 0.992, Sy,x = 0.021 mmol/L. Results were similar within each diagnostic group. Consistent agreement between adjusted and ionized calcium was observed in 96.7% of patients representing a variety of the most frequently encountered disorders of calcium metabolism. Thus we find adjusted ionized calcium to be as useful as actual ionized calcium for evaluation of patients with such disorders. Adjusted ionized calcium may therefore also be a logical choice for establishing agreement between laboratories for reference intervals in healthy adults.

Adjusted ionized calcium (at pH 7.4) and actual ionized calcium (at actual pH) in capillary blood compared for clinical evaluation of patients with disorders of calcium metabolism

Groups comprising 42 recurrent and 38 single calcium stone formers, and 48 controls underwent a standardized study protocol During 12 h of fasting along with a standardized water load urine was collected for the last 4 h One blood sample was drawn midway during urine collection As compared with controls recurrent stone formers demonstrated significantly raised values of plasma ionized calcium, 1,25-dihydroxyvitamin D [1,25-(OH)2D], urinary ionized calcium, urinary pH, and standardized excretion rate of calcium [ECa(U)] The tubular reabsorption of sodium and chloride, the maximal tubular reabsorption of phosphate, nephrogenous cyclic AMP (NcAMP), glomerular filtration rate (GFR) and plasma albumin were all significantly depressed Data from the single stone former group were intermediate between controls and recurrent stone formers For the pathogenesis of recurrent calcium stone formation these data suggest a general, though variably expressed, defect in the proximal tubular reabsorption of calcium, phosphate, bicarbonate, sodium and chloride leading to hypersecretion of 1,25-(OH)2D, hyperabsorption of calcium from the gut and a modest increase in plasma ionized calcium Computer analysis of data do not support the concept that stone patients can be classified as either intestinal hyperabsorbers or renal losers A stepwise discriminant analysis selected plasma albumin, urinary pH, ECa(U), plasma phosphate, GFR and NcAMP as the most important variables contributing to the difference between controls and recurrent stone formers By this procedure we obtain a sensitivity of 93% and a specificity of 96% respecting proper classification of the recurrent stone former The analysis may therefore be of value predicting the risk of recurrent stone formation in the single stone former

S N Holmegaard

Papers

Adjusted ionized calcium (at pH 7.4) and actual ionized calcium (at actual pH) in capillary blood compared for clinical evaluation of patients with disorders of calcium metabolism

Simplified protocol for biochemical evaluation of recurrent renal calcium stone disease.