Background: The problem of spurious hyperkalaemia in blood samples
delivered to hospitals from local general practitioners' (GP) surgeries remains a
source of diagnostic confusion and potential danger to patients. We have carried out
retrospective and prospective audits of serum potassium measurements to assess the
influences of blood sample delivery time and temperature during transit from GP
surgeries to a centralized laboratory on the risk of spurious serum potassium
measurements.
Method: The retrospective audit included serum potassium measurements
made by the pathology laboratory at Addenbrooke's Hospital on 51 843 patients
attending either the hospital itself or one of 62 local GP surgeries during the
months August 2001 to February 2002 (i.e. summer through to winter). The probability
of spurious potassium measurements on GP patients relative to blood sample delivery
time and temperature was modelled by least-squares multiple linear regression. The
prospective audit included serum potassium measurements made on 40 patients
presenting early in the day at the Sutton GP surgery near Ely, Cambridgeshire, during
the months February to May 2002.
Results: Low blood sample delivery temperature had a greater impact on
the probability of spurious potassium measurements than long delivery time. Low
delivery temperature also had a greater impact on the probability of spurious
hyperkalaemia than it had on the probability of spurious normokalaemia. At
temperatures below 20.3°C, the probabilities of both spurious hyper- and
normokalaemia for samples delivered from the most distant and closest GP surgeries to
Addenbrooke's increased significantly.
Conclusions: Maintaining blood sample delivery temperatures a few
degrees above 20°C will minimize the risk of spurious serum potassium measurements on
samples from GP patients.
