Interpretation of Quality Control Data Laboratory Operations Review 50
TERM EXPLANATION
Control limits
Levey-Jennings chart
Range within which control values must fall for assay to be considered valid. Many labs use mean ±2 SD. 1
determination in 20 will fall outside ±2 SD. This is anticipated part of normal variation.
Normal distribution curve lying on its side, marked with mean, ±1, ±2, ±3 SD.
2
+ 2 S.D.
+ 1 S.D.
X
4 6 8 10 12
Day
14 16 18 20
Levey-Jennings chart showing in-control results. (From Strasinger SK, Di Lorenzo MS. Urinalysis and
Body Fluids, 5th ed. Philadelphia: FA Davis; 2008:133.)
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