A Need for Standardisation in D-Dimer Testing: Evidence from a Collaborative Study by the UK NEQAS and QMP-LS Quality Assessment Programmes

Abstract number: P1898

Jennings¹ I, Raby² A, Kitchen¹ S, Woods¹ TAL, Kitchen¹ DP, Crowther² M, Walker¹ ID, Preston¹ FE

¹¹UK NEQAS for Blood Coagulation, Sheffield, UK ²²QMP-LS, Ontario, Canada

Background:  D-Dimer measurement is useful for monitoring many disease states, including DIC, and in the exclusion of DVT/PE. Recently, D-Dimer levels have been shown to predict thrombosis recurrence and may offer a strategy for patient-tailored anticoagulant regimes. However, no international standards are available for D-Dimer, and between-method variation has previously been observed. We report here findings from a collaborative exercise involving the UK National External Quality Assessment Scheme (UK NEQAS) and the Quality Management Program – Laboratory Services (QMP-LS), Ontario, Canada. Three samples (DD0401, DD0403 and DD0404) with different D-Dimer levels were distributed to 432 UK NEQAS and 120 QMP-LS centres. Each centre was asked to perform a routine D-Dimer measurement. UK NEQAS centres were also requested to report interpretations based on three clinical scenarios.

Results:  In the UK, 71 centres reported qualitative or semi-quantitative results, and 361 centres reported quantitative levels of D-Dimer. The median D-Dimer level (range) for sample DD0401 was 287 ng/mL (48–671); DD0403 632 ng/mL (112–1300); DD0404 933 ng/mL (140–2700). In Ontario, 83 centres reported qualitative or semi-quantitative results and 48 centres reported quantitative levels of D-Dimer. The median D-Dimer level (range) for sample DD0401 was 280 ng/mL (97–365), for DD0403 was 584 ng/mL (174–1050) and for DD0404 was 855 ng/mL (171–1852). Markedly different values were obtained with different commercial kits [eg sample DD0404, Dade-Behring median 260 ng/mL (n= 30), Inst. Lab. median 918 ng/mL (n= 116)]. There was also a lack of concordance in interpretations; 40% of UK centres reported ‘DVT excluded’ for sample DD0401 if in conjunction with a low pretest probability, whilst 57% reported that a DVT could not be excluded.

Conclusion:  Standardisation of D-Dimer measurement is an international problem, and there is a need for development of an international reference material.