Anticoagulant-induced preanalytical errors in ionized calcium determination on blood

Abstract

When anticoagulated blood is necessary for ionized calcium (Ca²⁺) measurements especially in urgent circumstances, the type (sodium or ‘calcium-titrated’ heparinate) as well as the form (aqueous or dry) of anticoagulant induce preanalytical errors.

To quantify these modifications Ca²⁺ was measured in three aqueous solutions and in three serum pools in different ‘sampling’ conditions.

Incomplete syringe filling and specimen volume/syringe nominal volume ratio effects were tested. Syringes were rinsed (i) with saline to yield ‘pure’ dilution effect (‘solution-dilution’); (ii) with sodium heparinate to study binding; (iii) with calcium-titrated heparinate to evaluate ‘calcium-distortion’.

All types of errors increased when syringes were not filled to their nominal volume, especially on small-sized specimens. Detailed tables provide percentage error values for all sampling conditions. Thus, ‘solution-dilution’ can reach -5%; binding is always important (-15 to -50%). ‘Calcium-distortion’ is minimal, around 1.25 mmol/1 Ca²⁺, but can reach -7% for high Ca²⁺ and +10% for low Ca²⁺.

Key Words:

• binding
• dilution
• specimen volume/syringe volume ratio