Background Blood from central venous or arterial catheters as well as from fingersticks is often used for point-of-care glucose testing.

Objectives To compare glucose values obtained with a point-of-care device for catheter and fingerstick blood samples with values obtained by clinical laboratory analysis of a catheter blood sample.

Methods A method-comparison design was used. Point-of-care values for fingerstick and catheter blood samples were compared with laboratory values for blood from catheters in a convenience sample of 63 critically ill patients. Device bias and precision were calculated and graphed according to the Bland-Altman method, and a t test was used to determine differences in glucose values for the 2 methods.

Results Laboratory glucose values for blood from a catheter sample differed significantly from point-of-care values for blood from a fingerstick (t1,61 = 5.01; P < .001) and from a catheter (t1,61 = 3.91; P < .001). Bias and precision for the point-of-care device was large (fingerstick, 8.7 and 13.7; catheter, 7.0 and 14.0); 20% of the values differed from the laboratory glucose values by more than 20 mg/dL. Point-of-care glucose values for fingerstick and catheter samples did not differ (P = .41).

Conclusions Glucose values obtained with a point-of-care device differ significantly from those obtained by laboratory analysis. The magnitude of these differences calls into question the widespread practice of using point-of-care glucose testing to guide insulin titration for tight glucose control. Errors in dosing could easily be made because of the large bias and precision associated with a point-of-care device.

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