Background Blood for glucose analysis is often obtained interchangeably from indwelling catheters and fingersticks. Objectives To determine the level of agreement between glucose values obtained by laboratory analysis and with a point-of-care device for blood from 2 different sources: fingerstick and a central venous catheter. Methods A method-comparison design was used. Point-of-care values for blood from fingersticks and catheters were compared with laboratory values for blood from catheters in a convenience sample of 67 critically ill patients. The effects of hematocrit level and finger edema on differences in glucose values between the 2 methods were also evaluated. A t test was used to determine differences in glucose values obtained via the 2 methods. Differences and limits of agreement were also calculated. Results Laboratory glucose values for blood from a catheter differed significantly from point-of-care values for blood from the catheter ( t 1,66 = −9.18; P < .001) and from a fingerstick ( t 1,66 = 6.53; P < .001). Glucose values for the 2 methods differed by 20 mg/dL or more for 1 of 6 patients (15%) for catheter samples and for 1 of 5 (21%) for fingerstick samples. Point-of-care glucose values for fingerstick and catheter samples did not differ ( P = .98). Hematocrit level significantly explained the difference in glucose values between the 2 methods for both catheter ( R 2 = 0.288; P < .001) and fingerstick ( R 2 = 0.280; P = .02) samples. Conclusions Use of a commonly used point-of-care device when precise glucose values are needed may lead to faulty treatment decisions.