Methods: Samples from 406 patients from nine general practitioners (GPs) in two Danish counties were
sent to two hospitals for analyses, during two periods
(winter and summer). Transport conditions (mail,
courier pick-up, or brought to hospital by public
coach), storage time, storage temperature and centrifugation requirements were different in the two
counties. Results were tested for deviation from a ‘‘0-
sample’’, the blood sample taken, centrifuged and
separated at the doctor’s office within 45–60 min. This
sample was considered as the best estimate of a comparison value