![]() ![]() As with the NSGP certification, two out of the three samples must demonstrate accuracy within 6% of the NGSP target values for any assay methods to pass the CAP survey. In the past 5 years (thus for 10 surveys), the low reference A1C range has been between 5.1 and 6.6%, the medium range between 5.65 and 7.6%, and the high range between 8.05 and 9.8%. In the CAP program, three pooled, whole-blood reference samples consistent with a low, medium, and high A1C level are mailed to ∼2,000 participating individual clinical laboratories, which then analyze them in the same manner they would patient samples and return the results to CAP ( 19). Contrary to the NGSP annual certification, which demonstrates accuracy under optimal and standardized conditions, the CAP glycohemoglobin (GH2) survey provides information about accuracy and precision when assay methods are used in clinical and realistic environments, including potential influence caused by end-users. The College of American Pathologists (CAP) also conducts biannual proficiency testing of A1C instruments ( 18). As of March 2014, the Bayer (now Chek Diagnostics) A1CNow, Siemens DCA Vantage, and Axis-Shield Afinion were the only three NGSP-certified A1C POC devices. Based on the stringent criterion set by the NGSP and its alignment with DCCT results, the American Diabetes Association (ADA) endorsed the NGSP and specifically recommends that laboratories use only methods that have passed NGSP certification ( 13, 16, 17). This tight criterion provides practitioners confidence in the accuracy and precision of these devices under “optimal conditions” ( 9, 15). Certification results when at least 37 of the 40 samples fall within 6% (lowered from ☑5% in 2007) of the NGSP secondary reference laboratory values ( 7). The 40 individual samples are distributed over an A1C range of 4–10%. To ensure continued accuracy, the NGSP requires annual manufacturer certification, during which the A1C assay device must be tested in a 40-sample comparison against an NGSP secondary reference laboratory in a controlled environment. The DCCT, a primary-prevention cohort study, established the direct relationship between A1C and long-term complication risk in patients with type 1 diabetes ( 14). Since its development in 1996 under the direction of the American Association for Clinical Chemistry, the NGSP has been the authority in establishing guidelines and protocols for standardizing A1C testing for both POC and laboratory instruments to Diabetes Control and Complications Trial (DCCT)-equivalent values ( 7, 13). The ability of a POC instrument to most closely replicate the actual A1C of any given patient is paramount ( 12). ![]()
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