Q: Can the manufacturer's stated ranges be used as the laboratory's quality control ranges?
A: The standards require each laboratory to establish their own control ranges through repetitive testing. However, there is an allowance to use manufacturer ranges when the following conditions are met:
- the stated values correspond to the method and instrument used by the laboratory, and
- the mean obtained by the laboratory reflects the manufacturer's stated mean, and
- the Laboratory Medical Director assures the range is narrow enough to detect clinically significant error.
Manufacturer ranges may also be implemented if a test is used so infrequently that calculation of valid statistics is not possible. In settings where there is a high reproducibility (precise instrumentation, limited testing personnel), the laboratory's own calculated standard deviation (SD) may be small. When compared with the manufacturer ranges, a laboratory may find that the range spans more than the commonly used +/-2 SD. Using the laboratory's calculated +/-2 SD may produce unnecessarily narrow ranges, causing the testing personnel to frequently repeat QC and investigate when the controls performs outside the laboratory's range, but within the manufacturer's range. Alternatively, the full manufacturer range may be too broad to promote the detection of clinically significant error. Selection of the appropriate range is a balance between these two ends of the spectrum.
It is at the determination of the Laboratory Medical Director to approve quality control ranges after giving consideration to the clinically significant variance as compared to the statistically derived SD.