Comparison of Plasma With Whole Blood Prothrombin Time and Fibrinogen on the Same Instrument

• Published in: American journal of clinical pathology Vol. 133; no. 4; pp. 550 - 556
• Main Authors: AMUKELE, Timothy K, FERRELL, Chris, CHANDLER, Wayne L
• Format: Journal Article
• Language: English
• Published: Chicago, IL American Society of Clinical Pathologists 01.04.2010
• Subjects: Automation, Laboratory; Biological and medical sciences; Blood Physiological Phenomena; Blood Specimen Collection - instrumentation; Fibrinogen - analysis; Hematocrit - instrumentation; Humans; International Normalized Ratio - instrumentation; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Plasma - physiology; Prothrombin Time - instrumentation; Blood coagulation; Instruments; Point of care; Hematocrit; Coagulation; Blood plasma; Whole blood; Anatomic pathology; Prothrombin time; Point of care testing; Coagulation test; Fibrinogen; Comparative study
• ISSN: 0002-9173; 1943-7722
• DOI: 10.1309/AJCPLDT9OVX1TDGT

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; r(2) = 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 (r(2) = 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.