No requirements exist as to which TDM analyses Norwegian laboratories should perform, neither in large nor in small hospitals. Local variations are therefore considerable. The purpose of this article was to establish an overview of the combined national TDM repertoire for blood/serum. The overview can be used as a tool by clinicians who need to know which analysis can be performed, and where. For the staff at clinical biochemistry and pharmacological laboratories, it may also be beneficial to know where to forward samples for analyses that they do not perform themselves.
The data collection process for this article turned out to be more complicated than we assumed at the outset. The organisational structure of the hospitals was rarely intuitive, and without local knowledge it was difficult to predict which institutions would have their own laboratories. We therefore attempted to use each laboratory as a source to identify other laboratories in the same region, and we believe that we have succeeded in this.
Large hospitals represented an extra challenge, since the same institution could be host to several laboratories. In these cases – where the laboratories were located close to each other – we merged the analyses into a single repertoire. In cases where the laboratories were more distinctly separated in terms of geography and function, such as in Oslo University Hospital, we chose to present the laboratories individually.
This overview must be considered to have a restricted shelf life. The laboratories’ TDM repertoire is constantly changing, which can be illustrated by the digitalis glycosides digitoxin and digoxin. Digitoxin was withdrawn from the market while this study was underway (5), and many patients who used to take digitoxin now take digoxin. This has implied a change in the need for analyses. At the time of the first request (in late 2011), digitoxin and digoxin were analysed by 33 and eight laboratories respectively. At the time of the update in August 2012 numbers had changed to 30 and 29.
Despite the fact that this overview represents a «snapshot» of the situation prevailing in August 2012, we nevertheless consider that it may serve as a useful reference. It is important, however, to be aware that pharmacological laboratories will often be capable of performing a wider repertoire of analyses than those listed in this overview. If the laboratory has access to reference material of the substance to be analysed, a rough chromatographic analysis can usually be developed within a relatively short period of time. To achieve a precise quantification, however, the method of analysis must be validated, preferably through internal and external quality control programmes. This is very resource-intensive. Therefore, pharmacological laboratories tend to remove rarely performed analyses from their routine TDM repertoire, and rather keep these in a separate «research and development repertoire». Such analyses – not shown in this overview – may be requested in special cases, in agreement with the performing laboratory.