Variations in sample pH and pO2 affect ExacTech meter glucose measurements

A study was conducted to assess the effect of changes in sample pH and pO2 on the Accutrend, ExacTech Companion, Glucometer II, One Touch II, and Refloflux II blood glucose meters. Venous blood was tonometered after the addition of strong acid or alkali to produce 10 samples with a pH range of 6.54 to 7.73 but with a similar mean pO2 (9.09 +/- 0.096 (SEM) kPa) and pCO2 (5.52 +/- 0.024 kPa). The ExacTech showed a > 15% deviation from the value obtained at pH 7.40 below pH 6.95 and above pH 7.85 (r = 0.69, p = 0.026). Ten further samples were made with a pO2 range of 2.0 to 33.6 kPa but mean pH (7.28 +/- 0.012) and pCO2 (7.98 +/- 0.25 kPa) kept alike. The ExacTech was accurate at pO2 = 11.5 kPa but deviated by > 15% below pO2 = 5.8 kPa and above 22.9 kPa (r = -0.95, p = 0.00002). The Accutrend and One Touch II required a pO2 change of 42 and 45 kPa to achieve the same error (r = -0.82 and r = -0.67 respectively). Thus caution is required in the interpretation of ExacTech glucose measurements in severely acidotic or hypoxic patients.