Correlation of capillary and venous blood glucometry with laboratory determination

During resuscitation in the Singapore Armed Forces, blood glucose samples are often obtained for analysis using the capillary glucometer. A drop of venous blood from the intravenous cannula is sometimes used to ascertain the patient's blood glucose level. Venous samples may be sent to a commercial laboratory, but this does not allow immediate results.

To establish the correlation between the glucose levels of the capillary fingerprick sample analyzed by the glucometer (Cap), the venous sample analyzed by the glucometer (Ven), and the venous sample tested by the commercial laboratory (Lab).

This multicenter, prospective study enrolled subjects from Selarang, Clementi, and Maju Camp Medical Centers in the Singapore Armed Forces from November 2002 to January 2003. All subjects provided at least two samples; because provision of the capillary blood glucose sample was voluntary, only some gave consent for capillary fingerprick and provided three samples. There were no exclusion criteria. Bland-Altman plots were then constructed to compare the capillary and venous-on-capillary values with the laboratory results.

A total of 270 subjects were recruited. One hundred seventy subjects (63.0%) gave consent for capillary glucose measurement and, thus, had three readings for comparison. There was a mean difference of 0.97 mmol/L (17.46 mg/dL) between the Ven and Lab results. There was an insignificant mean difference of 0.01 mmol/L (0.18 mg/dL) between the Cap and Lab results.

Capillary whole-blood glucose values best approximated venous plasma glucose values from the laboratory. Measuring the venous whole-blood glucose using the glucometer resulted in an overestimation of the venous plasma glucose compared with the laboratory result by about 0.97 mmol/L (17.46 mg/dL). This may result in the withholding of intravenous glucose for patients who are actually hypoglycemic.