7: Westgard Rules & Troubleshooting

When is QC performed?

• beginning of shift

• after an instrument is serviced

• reagent lots changed

• after calibration

• inappropriate Pt results

Which QC management program:

• external agency

• unknown specimens tested by lab

• results reported to agency

• 3x a year

proficiency testing programs

Which QC management program:

• based on performance data from daily testing and internal QC

interlaboratory QC programs

req at least 2 QC materials per day for each nonwaived method

CLIA ‘88

• change in the mean of the control values

• trend or shift in control values

systemic error

QC results distributed on one side of the mean for 5-7 consecutive days

shift

What can cause shift?

• sudden failure or change in the light source

• change in reagent formulation

• change of reagent lot

• major instrument maintenance

• inaccurate calibration/recalibration

gradual change in control values; increase or decrease consistently over 5-7 consecutive days

trend

What can cause trend?

• deterioration of instrument light source

• gradual accumulation of debris in sample/reagent tubing

• gradual accumulation of debris on electrode surfaces

• aging of reagents

• gradual deterioration of control materials

What does the first number of Westgard rules mean?

number of control measurements

What does the subscript of a Westgard rule mean?

control limit

cotrol outside the mean +/- 2s

1-2s

Which Westgard rule is a warning, okay to accept?

1-2s

control is outside the mean +/- 3s

1-3s

2 consecutive controls exceed the mean +/- 2s on same side of the mean; within run and across runs (level 1 & 2 or same level 2 consecutive days)

2-2s

within run

2 levels

across runs

consecutive days

level 1 exceeds the mean +2s and level 2 exceeds the mean -2s (within run)

R-4s

10 consecutive control measurements fall on one side of the mean

10x

Steps for troubleshooting

• review QC plots and ID concerning trends, shifts, or other abnormal characteristics

• review expiration dates of all reagents, QC, and calibration material

• verify no major instrument failures or maintenance occurred within the timeframe of concern

• attempt reanalysis with fresh QC

• attempt reanalysis w/ new and unopened QC material

• attempt reacalibration w/ fresh calibrator and reanalyze QC

• attempt recalibration w/ new calibrator material from a different lot

• escalate to lab supervisor, director, and/or manufacturer