Actual ionized calcium and pH in blood collected in capillary or evacuated tubes

Abstract

Thode J. Actual ionized calcium and pH in blood collected in capillary or evacuated tubes. Scand J Clin Lab Invest 1986; 46: 89-93.

Results are presented for the concentration of actual ionized calcium (^cCa²⁺), the actual pH and ionized calcium at pH=7.4 [^cCa²⁺(7.4)] measured in capillary whole blood, venous serum from vacuum tubes (Venoject) and serum equilibrated to pCO₂₊ = 5.3 kPa from 57 renal patients. The mean value for ^cCa²⁺ was higher for venous serum than for capillary blood (1.29 mmol/l versus 1.26 mmol/l), corresponding to the difference in pH (in venous serum). This difference could be eliminated by separating the serum at 4 ^cC rather than room temperature. The ^cCa²⁺ (7.4) was the same for capillary blood, venous serum (Venoject) and equilibrated serum from blood collected in plain glass tubes, Venous serum could be stored at 4 ^cC for 4 h without significant change in ^cCa²⁺ and pH, and for 1 week at 4 °C for the measurement of ^cCa²⁺(7.4). In patients with acid-base disturbance ^cCa²⁺ is preferable to the measurement of ^cCa²⁺ (7.4).

Key Words:

• anaerobic
• glycolysis
• ionized calcium at pH=7.4
• ion-selective electrodes
• serum
• storage
• temperature