I had occasion to read an article about advice about reporting or suppressing results when samples are hemolyzed. The article is here (available without a subscription).
Since the article was published in Clin Chem Lab Med, I sent in some thoughts to that journal as a letter. It was rejected the very next day with the reviewer not very happy with my letter. So in this blog entry, I will summarize the advice of this committee (EFLM) and my comments.
These days, most analyzers produce automatically a measurement of hemolysis – the H index. If one has performed an experiment to determine the effect of hemolysis on an analyte, one can subsequently approximate that effect by knowing the H index of a sample.
EFLM suggests that if the bias caused by hemolysis interference is greater than the RCV (reference change value), then the result should be suppressed. One would know this based on the reported H index. (The RCV represents a clinically significant error and if exceeded may cause the clinician to make an incorrect medical decision).
Here’s the problem – illustrated for the case where the assay CV=3% and the RCV=15%.
EFLM is allowing the hemolysis interference to take up 100% of the allowable error. But any result has at least three error sources: bias, interference(s), and imprecision. If one assumes that a result has no bias and the only interference is just below 15% and due to hemolysis, imprecision will still be present and cause (on average) the result be greater than the RCV 50% of the time. If one wanted to guarantee that 95% of the time, hemolysis interference didn’t cause the result to be greater than the RCV, the allowable limit for hemolysis interference would need to be 10.1% (15-(1.64×3)). And the 10.1% would still be optimistic because it assumes zero bias and zero interferences from other sources.
Manufacturers would never allocate 100% of allowable error to an interfering substance. Rather, manufacturers allocate error allowed by various error sources so that the total error is within goals. A rule of them that we used was any interference must have an effect less than 50% of the total allowable error.
So that’s a simple comment and I don’t see why the reviewer got so upset.