Preparing a quality control material for blood gases, pH and hemoglobinometry using stroma-free hemoglobin solution

Abstract

Properties of a quality control material for blood gases and pH should be similar to normal human whole blood with respect to oxygen buffering and acid-base behaviour. A hemoglobin solution may potentially fulfill this. However, the drawbacks of such a solution are the high oxygen affinity (lowp50), especially when it is prepared from human blood, and the improper concentration of bicarbonate. Bicarbonate is added to human stroma-free hemoglobin solution (SFHS), prepared as described previously, to obtain the desired pH and pCO2 combinations. Tonometry was used to determine the appropriate concentration of bicarbonate, which is 22.5 mmol/L to obtain an acidotic, and 29 mmol/L for both an alkalotic, and normal pH and pCO2 combination. Inositolhexaphosphate (IHP) is added to SFHS containing bicarbonate to obtain a normal p50 (around 3.55 kPa). Tonometry was used to determine the molar ratio of IHP/Hb4 (mol/mol) at which this is achieved. The molar ratios of IHP/Hb4 are 1.52, 1.74 and 3.40 for preparations with an acidotic, normal and alkalotic pH, respectively. In human SFHS nHill is 2.55 in the absence of IHP,nHill is at minimum 1.71 at a molar ratio IHP/Hb4 of 1.86 and increases to 2.53 at a molar ratio IHP/Hb4 of 5.04 and higher. Because the p50 will decrease with chi Hi this was studied at molar ratios of IHP/Hb4 of 0, 2 and 4, which covers the range of ratios as used. At these molar ratios of 0, 2 and 4, the decrease in p50 is 0.017 kPa/%Hi, 0.023 kPa/%Hi and 0.028 kPa/%Hi, respectively. Because bovine Hb was p50 near that of normal human blood, it is also used. The oxygen affinity shows a small decrease (p50 increases from 3.05 to 5.27 kPa) on addition of IHP. In the absence of IHP, nHill is 2.51 and nHill is at maximum 3.35 at molar ratios IHP/Hb4 between 3.00 to 4.56. At higher molar ratios nHill decreases to 2.90.