IFCC recommendation on sampling, transport and storage for the determinationof the concentration of ionized calcium in whole blood, plasma and serum

Abstract

The substance concentration of ionized calcium (c Ca2+) in blood, plasma or serum preanalytically may be affected by pH changes of the sample, calcium binding by heparin, and dilution by the anticoagulant solution. pH changes in whole blood can be minimized by anaerobic sampling to avoid loss of Co2, by measuring as soon as possible, or by storing the sample in iced water to avoid lactic acid formation. cCa 2+ and pH should be determined simultaneously. Plasma or serum: If centrifuged in a closed tube, and measured immediately, the pH of the sample will be close to the original value. If a delay has occurred between centrifugation and the measurement, causing substantial loss of Co2, equilibration of the sample with a gas mixture corresponding to pCO2= 5.3 kPa prior to the measurement is recommended. Conversion of the measured values to cCa 2+ (7.4) is only valid if the pH is in the range 7.2-7.6. Ca2+ binding by heparin can be minimized by using either of the following: (1) A final concentration of sodium or lithium heparinate of 15 IU/ml blood or less (2) Calcium titrated heparin with a final concentration of less than 50 IU/ml blood. Dilution effect can be avoided by use of dry heparin in capillaries or syringes. When heparin solutions are used, errors due to dilution or calcium binding can be reduced by using syringes with a heparin solution containing free calcium ions corresponding to the mean concentration of ionized calcium in normal plasma. Conditions for blood collection, storage, and transport to avoid preanalytical errors are described in this paper.

Forty mouse strain survey of voluntary calcium intake, blood calcium, and bone mineral content

“…In addition, we used a stopwatch to measure the time between when the mouse was removed from its cage and when the first tube of blood was collected. Ionized calcium concentrations were adjusted for pH using a standard formula [11].…”

“…In addition, we used a stopwatch to measure the time between when the mouse was removed from its cage and when the first tube of blood was collected. Ionized calcium concentrations were adjusted for pH using a standard formula [11].The other sample was centrifuged and resulting plasma analyzed for total calcium using a colorimetric method (Sigma Chemical Corp., kit no. 587) that was miniaturized to use 2.5 µl plasma and a 96-well plate format.…”

“…Ionized calcium is pH-sensitive and during sample processing, blood pH increases due to the loss of dissolved CO 2 . To account for this, measured ionized calcium concentrations are routinely adjusted according to a standard formula [11]. This practice, while appropriate in the clinic, would obscure intrinsic differences in blood pH between strains.…”

Measuring Total Blood Calcium Displays a Low Sensitivity for the Diagnosis of Hypercalcemia in Incident Renal Transplant Recipients

“…Free or ionized calcium (iCa) is physiologically active and under homeostatic control but is not routinely determined because of technique-related limitations and higher costs (2). Therefore, total calcium (tCa) is routinely measured.…”

Preanalytical Procedures in the Measurement of lonized Calcium in Serum and Plasma

“…The IFCC has had a working group dealing with theoretical and practical problems in this field for many years. The group has published a series of documents and recently a summary was published in the Journal of IFCC (2), based on the IFCC recommendations (3). The present study provides a basis for evaluating the risk of violating the recommendations.…”