Levey-Jennings QC Chart Formula: z-Score (1_2s / 1_3s), SDI & Peer CV Ratio (CVR)

Catch reagent drift and calibration shifts before patient results leave the analyzer!

Introduced to clinical pathology by Stanley Levey and E. R. Jennings (1950, Am. J. Clin. Pathol.) adapting Walter Shewhart’s industrial control charts, a Levey-Jennings Chart plots daily QC control-material measurements x_QC around established target Mean and analytical Standard Deviation s (with horizontal reference bands at +/- 1s, +/- 2s, and +/- 3s)! Converting each run into its standardized QC z-score z = (x_QC - Mean) / s immediately triggers Westgard single-run rules: |z| > 3.0 triggers 1_3s Out-of-Control Rejection (99.73% Gaussian confidence of analytical error — hold patient run!), while 2.0 < |z| <= 3.0 triggers a 1_2s Warning to inspect 2_2s, R_4s, and 4_1s multi-rules!

Furthermore, monthly inter-laboratory peer proficiency programs benchmark your lab’s Mean and SD against hundreds of peer analyzers via Standard Deviation Index SDI = (Lab_Mean - Peer_Mean) / Peer_SD (target |SDI| < 1.5, unacceptable >= 2.0) and Coefficient of Variation Ratio CVR = Lab_CV% / Peer_CV% (target CVR < 1.5)!

Levey-Jennings Daily QC Run z-Score & 1_2s / 1_3s Status

Computes signed z = (x_QC - Lab_Mean) / Lab_SD across today’s QC result B2, Lab Mean B3, and Lab SD B4 > 0.

=IF(B4 <= 0, "Requires Lab QC Standard Deviation > 0", ROUND((B2 - B3) / B4, 2))

Westgard Single-Run 1_2s Warning / 1_3s Rejection Decision Gate + Peer SDI

Flags In-Control (|z| <= 2), 1_2s Warning (2 < |z| <= 3), or 1_3s Reject Run (|z| > 3).

=IF(B4 <= 0, "Requires Lab QC Standard Deviation > 0", IF(ABS((B2 - B3) / B4) > 3, "1_3s REJECT RUN (|z| > 3s): Hold Patient Results & Troubleshoot", IF(ABS((B2 - B3) / B4) > 2, "1_2s WARNING (2s < |z| <= 3s): Check 2_2s, R_4s & 4_1s Rules", "In-Control Run (|z| <= 2s)")))

Further reading

• CLSI C24 — Statistical Quality Control for Quantitative Measurement Procedures