3. Primary Reference Laboratories (PRL)

PRLs serve as back-up laboratories for the CPRL to ensure that the CPRL function continues without interruption in the event that the CPRL cannot meet the program needs as outlined in section 2. All PRLs analyze GHB (HbA1c) using the primary reference method according to the CPRL method protocol.

a. Primary Reference Method Calibration: A single hemolysate calibrator is prepared by the CPRL; the target value is established by the CPRL based on the mean of at least 50 runs. All PRLs use this calibrator with assigned value to calibrate their instruments with each run according to the CPRL method protocol.

b. Primary Reference Method Quality Control: The CPRL prepares hemolysate QC specimens (two levels, a non-diabetic level and a diabetic level of at least 10% GHB) following the same protocol as for the calibrator preparation. Each PRL must establish their own QC mean and range criteria and accept or reject assays following the CPRL QC guidelines.

c. Certification of Traceability: A proposed PRL must perform precision testing following NCCLS EP5-A2 guidelines (1). The proposed PRL must also participate in a fresh blood sample comparison (n=100) for estimation of bias from the CPRL following modified NCCLS EP9-A2 guidelines (2). For bias estimation, fresh specimens are collected by either the proposed PRL or the CPRL and shipped to the other party. All data for calculation of precision as well as estimation of bias are submitted to the CPRL for analysis.

In order to be considered traceable to the CPRL: 1) total imprecision (CV) must not be statistically significantly >3%, 2) one within-method outlier is acceptable; one between-method outlier is acceptable, 3) 95% confidence interval for predicted bias should overlap the + 3% range of the CPRL at 2 GHB levels (6 & 9% HbA1c). All data analysis is performed by the NETCORE following NCCLS EP5-A2 and EP9-A2 guidelines. If criteria are not met, the proposed PRL may make changes as necessary, re-analyze the same set of samples from frozen aliquots and send the new set of data to the NETCORE for re-evaluation. Final certification of traceability is issued by the NETCORE after review of the data by the Steering Committee.

References:

  1. NCCLS. Evaluation of Precision Performance of Quantitative Measurement Methods; Approved Guideline;Second Edition. NCCLS document EP5-A2 (ISBN 1-56238-542-9). NCCLS, 940 West Valley Road, Suite 1400, Wayne, Pennsylvania 19087-1898 USA, 2004.
  2. NCCLS. Method Comparison and Bias Estimation Using Patient Samples; Approved Guideline;Second Edition. NCCLS document EP9-A2 (ISBN 1-56238-472-4). NCCLS, 940 West Valley Road, Suite 1400, Wayne, Pennsylvania 19087-1898 USA, 2002.