Abstract
AIMS--To examine the magnitude of thromboplastin and coagulometer interactions on the precision of International Normalised Ratio (INR) values when the manufacturers' recommended instrument specific International Sensitivity Index (ISI) values are adopted for the INR calculation. METHODS--The variability of INR values obtained from four automated phototopical coagulometers frequently used in North American laboratories was studied. When used with five commercial thromboplastins of moderate to high sensitivity (ISI values 0.92-1.97), 20 prothrombin time results were generated for each of a population of 98 patients on established warfarin treatment. RESULTS--The mean INR values of the patients ranged from 2.05 to 2.81, depending on which reagent/coagulometer combination was used. Within patient variation increased as the median INR value increased. The mean coefficient of variation of within patient INR values was 10%; the mean coefficient of variation of the prothrombin time results in seconds and prothrombin time ratio were 21 and 18%, respectively. CONCLUSIONS--There was considerable bias in the estimated ISI values of the thromboplastins compared with the manufacturers' instrument specific ISI value. Despite this apparent imperfection, our study clearly showed that the INR is preferable to other prothrombin time reporting formats for assessing the degree of anticoagulation for patients on warfarin treatment.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Ansell J. E. Imprecision of prothrombin time monitoring of oral anticoagulation. A survey of hospital laboratories. Am J Clin Pathol. 1992 Aug;98(2):237–239. doi: 10.1093/ajcp/98.2.237. [DOI] [PubMed] [Google Scholar]
- Becker D. M., Humphries J. E., Walker F. B., 4th, DeMong L. K., Bopp J. S., Acker M. N. Standardizing the prothrombin time. Calibrating coagulation instruments as well as thromboplastin. Arch Pathol Lab Med. 1993 Jun;117(6):602–605. [PubMed] [Google Scholar]
- Bussey H. I., Force R. W., Bianco T. M., Leonard A. D. Reliance on prothrombin time ratios causes significant errors in anticoagulation therapy. Arch Intern Med. 1992 Feb;152(2):278–282. [PubMed] [Google Scholar]
- Clarke K., Taberner D. A., Thomson J. M., Morris J. A., Poller L. Assessment of value of calibrated lyophilised plasmas to determine International Sensitivity Index for coagulometers. J Clin Pathol. 1992 Jan;45(1):58–60. doi: 10.1136/jcp.45.1.58. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ng V. L., Levin J., Corash L., Gottfried E. L. Failure of the International Normalized Ratio to generate consistent results within a local medical community. Am J Clin Pathol. 1993 Jun;99(6):689–694. doi: 10.1093/ajcp/99.6.689. [DOI] [PubMed] [Google Scholar]
- Peters R. H., van den Besselaar A. M., Olthuis F. M. Determination of the mean normal prothrombin time for assessment of international normalized ratios. Usefulness of lyophilized plasma. Thromb Haemost. 1991 Oct 1;66(4):442–445. [PubMed] [Google Scholar]
- Poller L., Taberner D. A., Thomson J. M., Darby K. V. Survey of prothrombin time in National External Quality Assessment Scheme exercises (1980-87). J Clin Pathol. 1988 Apr;41(4):361–364. doi: 10.1136/jcp.41.4.361. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Poller L., Taberner D. A., Thomson J. M., Morris J., Mibashan R. S., Shinton N. K. Effect of the choice of WHO International Reference Preparation for thromboplastin on International Normalised Ratios. J Clin Pathol. 1993 Jan;46(1):64–66. doi: 10.1136/jcp.46.1.64. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Poller L., Thomson J. M., Taberner D. A. Effect of automation on prothrombin time test in NEQAS surveys. J Clin Pathol. 1989 Jan;42(1):97–100. doi: 10.1136/jcp.42.1.97. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ray M. J., Smith I. R. The dependence of the International Sensitivity Index on the coagulometer used to perform the prothrombin time. Thromb Haemost. 1990 Jun 28;63(3):424–429. [PubMed] [Google Scholar]
- Taberner D. A., Poller L., Thomson J. M., Darby K. V. Effect of international sensitivity index (ISI) of thromboplastins on precision of international normalised ratios (INR) J Clin Pathol. 1989 Jan;42(1):92–96. doi: 10.1136/jcp.42.1.92. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Thomson J. M., Taberner D. A., Poller L. Automation and prothrombin time: a United Kingdom field study of two widely used coagulometers. J Clin Pathol. 1990 Aug;43(8):679–684. doi: 10.1136/jcp.43.8.679. [DOI] [PMC free article] [PubMed] [Google Scholar]