Laboratory Quality Assurance and QC Best Practices

Laboratory Quality Assurance (QA)

Laboratory Quality Assurance (QA) is a comprehensive management process designed to ensure that final results reported by a laboratory are accurate, reliable, and consistent with defined analytical goals.

Proficiency Testing (PT)

Proficiency Testing, also known as an External Quality Assurance Program (EQAP), serves several critical functions:

• Allows for the comparison of test performance between different laboratories.
• Involves a batch of samples delivered periodically from a program organizer (e.g., CAP) to each member lab. Test results are sent to the organizer for data analysis, and reports are returned to member labs to compare performance.

Internal Quality Control (IQC)

Internal Quality Control (IQC) is a vital component of laboratory quality assurance. QC procedures monitor daily analytical performance, typically utilizing commercial QC samples.

Systematic and Random Errors

• Trend: A gradual change from the mean, indicating a gradual loss of reliability in the test system (e.g., aging reagents, deterioration of instrument light sources, or accumulation of debris).
• Shift: A sudden change from the mean, caused by abrupt system failures (e.g., unstable incubation temperatures, sudden light source failure, or major instrument maintenance).
• Random Error: Any deviation from expected results, typically exceeding 3SD.

QC Sample Management

• Performed on a daily, shift, or batch basis.
• Utilizes samples with defined analytes and levels, processed in the same manner as patient samples.
• QC performance must meet established criteria before patient results can be reported.
• Out-of-control situations: If QC failure is detected, patient results must be held back, investigated, resolved, and re-validated.

Westgard Multi-Rules

• 1-3s: One control measurement exceeds the mean ± 3SD; reject the run (indicates large systematic error).
• 2-2s: Two consecutive control measurements exceed the mean ± 2SD; reject the run (indicates systematic error).
• R-4s: Two control measurements exceed the mean ± 2SD in opposite directions (one +2SD, one -2SD).
• 4-1s: Four consecutive control measurements exceed the mean ± 1SD.
• 10-x: Ten consecutive control measurements fall on one side of the mean (all positive or all negative).