Multicenter study of whole-blood creatinine, total carbon dioxide content, and chemistry profiling for laboratory and point-of-care testing in critical care in the United States

Objectives: To introduce a creatinine biosensor and a total carbon dioxide content (TCO₂) method for whole-blood measurements, to evaluate the clinical performance of a new transportable analyzer that simultaneously performs these two and six other tests (Na⁺, K⁺, Cl^-, glucose, urea nitrogen, and hematocrit), and to assess the potential of the new analyzer for point-of-care testing in critical care by comparing results obtained by nonlaboratory personnel and by medical technologists. Design: Multicenter sites compared whole-blood measurements with the transportable analyzer to plasma measurements from the same specimens with local reference instruments. One site compared whole-blood results produced by nonlaboratory personnel vs. medical technologists and evaluated day-to-day and within-day precision at the point of care. Settings and Patients: Four medical centers in the United States. Venous and arterial specimens from 710 critically ill patients with a variety of diagnoses. Point-of-care testing in the emergency room and operating room. Results: The linear regression analyses at the four medical centers showed the following: creatinine (a) slope, 0.91 to 1.22, (b) y intercept, -0.07 to 0.15 mg/dL, and (c) r², 0.77 to 1.00; and TCO₂: (a) slope, 0.64 to 1.00, (b) y intercept, 1.36 to 9.6 mmol/L, and (c) r², 0.52 to 0.72 (y(i), whole-blood analyses; x(i), plasma reference measurements). Bland-Altman plots also were used to assess multicenter creatinine and TCO₂ results. Of the other analytes, K⁺, glucose, and urea nitrogen had the highest r²)-values. For the eight chemistry profile tests performed at the point of care (y(i), nonlaboratory personnel results; x(i), medical technologist results), the average value of r² was 0.96 (SD 0.08) in the operating room and 0.96 (SD 0.06) in the emergency room, and mean paired differences (y(i) - x(l)) were not statistically or clinically significant. Precision was acceptable. Conclusions: The performance of the creatinine biosensor and the TCO₂ method was acceptable for whole-blood samples. Comparisons of whole-blood results from the transportable analyzer and plasma results from the local reference instruments revealed analyte biases that may be attributed to differences between direct whole-blood analyses and indirect-diluted plasma measurements and other factors. Performance of nonlaboratory personnel and medical technologists was equivalent for point- of-care testing in critical care settings. The whole-blood analyzer should be useful when patient care demands immediate results.