Posted by Sten Westgard, MS
An interesting question came in through email (we always want to hear from you!):
"1. Can we apply Westgard multirules to hematology control?
2. I read in one paper that the hematology control range is calculated as mean +/- 2.5 SD, is this correct and if not how can I calculate own laboratory hematology control range?"
The answer, after the jump...
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Posted by Sten Westgard, MS
We got an excellent question the other day via email:
I have heard the term "Within QC" and "Across QC"used, but what do these refer to specifically andwhere can I find more information about what ismeant by those terms? I was not able to find thisinformation, but laboratory leadership staff saidthat "Within QC" referred to assessing multi-rules"within QC level and across QC runs", and that"Across Qc" referred to assessing multi-rules"looking at both QC levels, can be within same runor back-to-back runs".A lab has the following multi-rules; "Within QC"1:3s, 1 QC result outside 3sd; 2:2s, 2 consecutiveQC results outside 2sd on the same side of the mean;4s, 2 consecutive Qc results differ by more than4sd; and 1:2s, 1 Qc result outside 2sd and within 3.(1:2s is used as a warning rule, the others asrejection rules). The rules for "Across Qc" are asfollows; 2:2s, 2 consecutive Qc results (1 eachmultiple levels) are outside of 2sd; and 4s, 2 Qcresults (one of each multiple levels) are >4sdapart. These are both rejection rules. Thesemulti-rules are used to assess all tests in achemistry lab; the majority of tests are assessedwith 2 levels of Qc, a few use 3 levels of Qc.The situation arose where QC results on one day fora cancer antigen were the following:Day 1A:Level 1 -Within 2sd, acceptableLevel 2 -1:2s, run was accepted as only the warningrule 1:2s was encountered.The next day the results were as follows:Day 2A:Level 1 -1:2sLevel 2 -Within 2sdLeadership said run should not be accepted,violating the "across" 2:2s rule.However, leadership said the inverse situation wouldhave been acceptable as *consecutive* data pointsdid not violate the "across" 2:2s rule, i.e.
Day 1B:Level 1 1:2sLevel 2 within 2sdDay 2B:Level 1 within 2sdLevel 2 1:2sIn the A group, because Level 2 is outside of 2s,and the very next data point (Level 1 from the nextday) is also out 2s, the run is unacceptable andshould be rejected. In Group B, since consecutivedata points are okay the run is acceptable.Is this a correct approach? Is it correct to rejectgroup A (Day 1A and 2A) and not reject group B (Day1B and 2B)? Do these multi-rules as outlined andimplemented detect some unacceptable variation ingroup A that does not exist in group B? Thank youfor any clarification.
So what's the answer? Are scenarios A and B fundamentally different? More after the jump.
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