Download PDF
Thromb Haemost 1988; 60(01): 018-020
DOI: 10.1055/s-0038-1647626
Original Article
Schattauer GmbH Stuttgart

A Simple Nomogram for the Derivation of International Normalised Ratios for the Standardisation of Prothrombin Times

L Poller
The UK Reference Laboratory for Anticoagulant Reagents & Control (WHO Collaborating Centre), Withington Hospital, Manchester, UK
› Author Affiliations
Further Information

Publication History

Received 18 December 1987

Accepted after revision 11 March 1988

Publication Date:
30 June 2018 (online)

Also available at
  PDF Download  Permissions and Reprints

Summary

The WHO international scale of reporting prothrombin time results is based on the calibration of local and commercial thromboplastin reagents used in the test against an international reference preparation to derive an International Sensitivity Index (ISI) for each batch of local reagent. This quantifies an individual reagent’s responsiveness to the coumarin induced defect.

Once the ISI has been assigned, the derivation of International Normalised Ratios (INR) for reporting results depends on the use of a scientific calculator by which the local ratio is raised to the power of the ISI of the local reagent or use of an alternative formula and logarithms.

A system for interpretation of INR, without the need for calculations, is presented for the known range of thromboplastins between 1.0 and 3.0 ISI in nomogram form. This chart may facilitate the general application of the INR system.

Key words

Prothrombin time - Standardisation - International Normalised Ratios - International Sensitivity Index
 

  • References

  • 1 Poller L, Thberner DA. Dosage and control of oral anticoagulants. An international survey Br J Haematol 1982; 51: 479-485
    CrossrefPubMedSearch in Google Scholar
  • 2 Taberner DA, Poller L, Burslem RW, Jones JB. Oral anticoagulants controlled by British Comparative Thromboplastin versus low dose heparin in prophylaxis of deep vein thrombosis. Br Med J 1978; i: 272-274
    PubMedSearch in Google Scholar
  • 3 Hull R, Hirsh J, Jay R, Carter C, England C, Gent M, Turpie AG, McLaughlin D, Dodd P, Raskob G, Ockelford P. Different intensities of anticoagulants in the long-term treatment of proximal vein thrombosis. N Engl J Med 1982; 307: 1676-1681
    CrossrefPubMedSearch in Google Scholar
  • 4 WHO Expert Committee on Biological Standardisation. 31st Report. WHO Tech Rep Ser 1983; 687: 81-105
    PubMedSearch in Google Scholar
  • 5 WHO Recommended Methodology for Using WHO International Reference Preparations of Thromboplastin. WHO; Geneva: 1985
  • 6 Loeliger EA. International Committee for Standardisation in Haematology. Recommendations for reporting prothrombin time in oral anticoagulant control Thromb Haemostas 1985; 53: 155-156
    PubMedSearch in Google Scholar