When we realized a couple of months ago that almost all the anti-Xa activities (to monitor heparin therapy) where measured in our lab on inappropriate samples, we decided that we would not measure any more anti-Xa activities without a prior knowledge of the precise mode - and rationale - of heparin administration, as well as the precise hours of blood sampling. Within a few weeks, the situation improved a lot, and now only a very few percents of the requests are inappropriate. We are quite confident that the figures will even soon drop to a few tenths of percent. We are now doing the same for all therapeutic-drug monitorings but similar figures are not as easily obtained with other drugs , for example with digoxin where "TDM" is in fact more likely to mean "suspicion-of-overdose" and where therefore we feel more reluctant to reject samples without further ado. Best regards, Joseph, Villefranche-de-Rouergue, France