Quick Review Cards for Medical Laboratory Science

Interpretation of Quality Control

Datacontinued

TERM EXPLANATION

Trend

Error, random

Error, systematic

False rejection

Control values increasing or decreasing for 6 consecutive runs.

Error that doesn’t recur in regular pattern, e.g., error due to dirty glassware, use of wrong pipet, voltage

fluctuation, sampling error, anticoagulant or drug interference. Indicated by control value significantly

different from others on Levey-Jennings chart, or violation of the 13Sor R4SWestgard rules. Usually a 1-time

error, & controls & samples can be rerun with success.

Recurring error inherent in test procedure, e.g., dirty photometer, faulty ISE, evaporation or contamination of

standards or reagents. Affects all results. Indicated by trend or shift on Levey-Jennings chart, or violation of 22S,

(^4) 1S, or 10×Westgard rules (see following). Requires investigation to determine cause.
Rejection of run because QC results indicate problem when none is present. Use of Westgard rules minimizes
false rejections.
24681012
Day
14 16 18 20

• 2 S.D.


• 1 S.D.

• 1 S.D.


• 2 S.D.

X

Levey-Jennings chart showing trend. (From Strasinger SK, Di Lorenzo MS. Urinalysis and Body Fluids,

5th ed. Philadelphia: FA Davis; 2008:133.)

Laboratory Operations Review 52