Comparative evaluation of unfractionated and low molecular weight heparins. Results of the French Etalonorme interlaboratory quality control
Houbouyan, L.L.; Goguel, A.F.
Annales de Biologie Clinique 51(2): 109-117
1993
ISSN/ISBN: 0003-3898 PMID: 8214808 Document Number: 405909
Four recent interlaboratory surveys have been conducted by the French National "Etalonorme" Group of Quality Control in Haematology, involving about 3,800 laboratories working in coagulation. They have been concerned with human lyophilised plasma samples heparinized in vitro either with unfractionated heparins (UFH), or with low molecular weight heparins (LMWH) (Fragmin 89 D, and Fraxiparin 90 A). The doses added simulated therapeutic situations or were on the border-line of over- or underdosage: UFHs 89 B3/B4, 0.14 and 0.22 IU/ml; 89 C3/C4, 0.3 and 0.4 IU/ml respectively; LMWHs: D3-A3, 0.6; and D4-A4, 1.2 IU/ml. Automated partial thromboplastin times (APTT) were prolonged at these high doses of LMWH, due to noticeable residual anti-IIa activity. A relationship between APTT and heparinaemia was observed with both types of heparin; sensitivities of cephalin reagents to heparin were also noted, but they were different for UFH compared to LMWH. Dispersion on APTT results was still high (CV: 12-23% for the UFH samples, 12-19% for the four LMWH samples). Dispersion on heparin determinations was higher for UFH than for LMWH, even for lower anti-IIa activity, but they involved more heterogeneous assays. The anti-Xa activity for LMWH samples was mainly determined using clotting assays (70% of the laboratories) with larger dispersions (CV: 32-37%), than those observed on amidolytic assays (CV: 28%); however, these amidolytic assays were performed in 90% of the laboratories with only two reagents available from a single manufacturer. The clotting techniques, more than the colorimetric assays, seemed to underestimate the high heparinaemias.