Correcting laboratory results for the effects of interferences: an approach incorporating uncertainty of measurement.
BACKGROUND
Results of numerical pathology tests may be subject to interference and many laboratories identify such interferences and withhold results or issue warnings if clinically erroneous results may be issued. Some laboratories choose to correct for the effect of interferences, with the uncertainty of the correction noted as a limitation in this process. We investigate the effect of correcting for the effect of interferences on the ability to release results within defined error goals using the effect of in-vitro haemolysis on serum potassium measurement as an example.


METHODS
A model was developed to determine the uncertainty of a result corrected for the effect of an interferent with a linear relationship between concentration and effect. The model was used to assess the effect of correction on the results which could be released within specified accuracy criteria.


RESULTS
Using the effects of haemolysis on potassium results as an example, the maximum amount of haemolysis in a sample that would change the result by > 0.5 mmol/L, with a frequency of 5%, was increased from approximately 1100 mg/L (no correction) to 8000 mg/L (with correction).


CONCLUSIONS
With modelling of the factors related to the uncertainties of results in the presence of interferences, it is possible to release results in the presence of significantly higher concentrations of interferences after correction than without correction. Correction of a result for a known bias and allowance for the uncertainty of the correction can be considered consistent with the guide to the expression of uncertainty in measurement (GUM).
St Vincent's Hospital, Sydney, Australia gjones@stvincents.com.au.
Graham R D
GR
Jones
Tan Tock Seng Hospital, Singapore.
Robert C
RC
Hawkins
D000465:Algorithms; D002624:Chemistry, Clinical / Q000379:methods*; D006461:Hemolysis; D006801:Humans; D016014:Linear Models; D015233:Models, Statistical; D011188:Potassium / Q000097:blood*; D011786:Quality Control; D015203:Reproducibility of Results; D035501:Uncertainty
D011188:Potassium
Analytical systems; laboratory methods; quality assurance and control