Re: Do we need BQL?

Date: Wed, 4 Aug 1999 15:39:27 +0100 (GMT) From: "J.G. Wright" <J.G.Wright@newcastle.ac.uk> Subject: Re: Do we need BQL? Dear Steve, I agree with everything you say below, but merely wished to represent the view taken from the people we actually have to convince (unfortunately not each other. Perhaps we should start some kind of campaign). I am not sure that the definition of QL etc will necessarily be consistent across labs. The difference between toxicokinetics and pharmacokinetics is that in pharmacokinetics we know the drug is there. To an extent you can argue that good modelling could be applied in toxicokinetics but I think the notion of a sample which is indistinguishable from a blank is simple and usefulin this context (and doesn't need extensive assumptions). Of course, this is not the same definition of QL as you suggest below. It corresponds more closely to your LOD. My comments about variability at very low concentrations were perhaps somewhat callous to modelling principles but what I was getting at is that in some circumstances crude approximations will work fine (few BQLs, consistent with other data), the trick is to see when they won't. Preferably in advance so you convince the people doing the assay. However, I am not for a second implying there is anything good about BQLs, they are a damned nuisance. The methodologies discussed are applicable to situations where you have bounded intervals for observations, not necessarily in BQL format. This could be some pharmacodynamic endpoint or a missing covariate (which happens all the time in every field) so the methods suggested have quite broad applicability. I think Thomas Forgues mentioned in his original email that they knew you shouldn't have BQL. What we need is a surefire method to convince the lab folks. I know that some labs do not even return samples with the label BQL but omit them entirely from the report, so perhaps it is a long way until we get to the BQL-less future. James