A critical limit protocol requiring that all point of care glucose meter readings > 22.2 mmol/L (400 mg/dL) and < 2.2 mmol/L (40 mg/dL) be immediately confirmed by the laboratory was assessed. A total of 193 (2%) of 9,523 glucose meter determinations (63 patients) were > 22.2 or < 2.2 mmol/L. One hundred twenty-two (63%) of critically high and low glucose readings were followed up, and 71 (37%) results were not. Seventy-seven percent (55 of 71) of results without follow up were in patients with multiple glucose meter/central lab comparisons, suggesting that users may have thought it unnecessary to confirm such results. Split sample quality control specimens showed good correlation (r = 0.927) between glucose meter and central lab results, whereas correlation for follow-up glucose results was poorer (r = 0.793), perhaps reflecting time delay in obtaining a lab sample. For follow-up results, only 18% of high/low critical limit glucose meter readings were confirmed by drawing a lab specimen within 10 minutes. Fifty-eight percent were in 17 patients with multiple previous glucose meter readings, suggesting that users may have though it less urgent to confirm a sequence of such results. Eleven follow-up results (9%) showed a > 50% discordance between glucose meter/central lab with three (27%) glucose meter errors, emphasizing the need to confirm critically high/low glucose meter results to avoid potential errors. The critical limit protocol now requires that only the initial critically high/low glucose meter reading be confirmed by the lab and that these patients now be followed with lab values until glucose levels are between 5.6-16.7 mmol/L (100-300 mg/dL) before the glucose meter can again be used.