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Can both EDTA and citrate plasma samples be used in measurements of fibrinogen and C-reactive protein concentrations?
Mika Skeppholm1, N Håkan Wallén, Margareta Blombäck
1Department of Clinical Sciences, Karolinska Institutet, Danderyd Hospital, Division of Cardiology, Stockholm, Sweden. mika.skeppholm@ds.se
Background:
Fibrinogen and C-reactive protein (CRP) concentrations are predictors of outcome in the atherosclerotic patient. It is important in risk stratification that these quantities are measured reproducibly in routine and research.
Method:
In the present study, we compare measurements of fibrinogen and high-sensitivity CRP in EDTA and citrate plasma samples (n=150) using nephelometric immunoassays. Fibrinogen was also measured in citrate plasma using a clotting method.
Results:
In approximately one-third of the samples, the fibrinogen concentration measured by immunoassay was higher in citrate plasma than in EDTA plasma, in spite of the dilution by citrate. The immunoassay results of fibrinogen concentration measurements in EDTA and citrate plasma differed significantly and also differed from those of functionally measured fibrinogen concentrations. A difference was found between the concentration of CRP in EDTA plasma and citrated plasma which also did not correspond to the dilution.
Conclusions:
Reproducibility of results is essential in risk stratification by fibrinogen or high-sensitivity CRP concentrations and small differences close to the decision limits may have a decisive impact. Immunological measurements are liable to confounding effects that may be difficult to foresee, qualitatively and quantitatively. Great care should be observed when measuring the concentration of calcium containing analytes in anticoagulated samples. Fibrinogen concentrations should preferably be measured functionally in citrate plasma.
