Comparison of plasma with whole blood prothrombin time and fibrinogen on the same instrument

Timothy K. Amukele, Chris Ferrell, Wayne L. Chandler

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


We compared plasma with whole blood (WB) international normalized ratio (INR) and fibrinogen using the same instrument and reagents. WBINRs were 50% higher than plasma INRs. After increasing the WB sample volume 40% and adjusting the International Sensitivity Index, WBINRs were similar to plasma INRs [adjusted WBINR = 0.99(plasma INR) - 0.02; r2 = 0.98; n = 155], but the average difference in WB vs plasma INR was 4-fold higher than duplicate plasma INRs. Variation in hematocrit was a major determinant of the accuracy of the WBINR, with increased error at high INRs. The WB fibrinogen assay was highly dependent on the sample hematocrit (r2 = 0.83), even after the sample volume was adjusted. Accurate WB fibrinogen measurements required a mathematical hematocrit correction. We conclude that WBINR and fibrinogen assays can be performed on point-of-care or automated analyzers, but sample volume must be adjusted to account for hematocrit. Accuracy is limited by variations in hematocrit with worsening accuracy for samples with high INRs or low fibrinogen levels.

Original languageEnglish (US)
Pages (from-to)550-556
Number of pages7
JournalAmerican Journal of Clinical Pathology
Issue number4
StatePublished - Apr 2010


  • Coagulation
  • Fibrinogen
  • Hematocrit
  • Point of care
  • Prothrombin time
  • Whole blood

ASJC Scopus subject areas

  • Pathology and Forensic Medicine


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