PubMed · 15643766
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Kandice Kottke-Marchant, Raymond D Aller, Wayne L Chandler. 2003. Coagulation analyzers.. https://pubmed.ncbi.nlm.nih.gov/15643766/
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In a Dutch project for harmonisation of factor VIII coagulant activity (FVIII:C) assays, the commutability of potential calibrators for FVIII:C was assessed by means of a 'twin-study design', which is in essence a multi-centre, split-patient sample, between-field-methods protocol. Commutability was defined as the degree to which a material yielded the same numerical relationships between results of measurements by a given set of measurement procedures as those between the expectations of the relationships for the same procedures applied to those types of material for which the procedures were intended. The study consisted of the simultaneous analysis of fresh frozen patient plasmas and three potential calibrators for FVIII:C by 16 Dutch laboratories forming eight couples. The state-of-the-art intra-laboratory standard deviation was used to assess the commutability of the potential calibrators. One potential calibrator was used to harmonise FVIII:C assay results in a Dutch field study. The inter-laboratory coefficient of variation of two test samples could be reduced significantly, but no significant effect was observed with three other test samples. We recommend that at least three different sample dilutions be used in each FVIII:C assay, in agreement with previous recommendations.
BACKGROUNDS AND OBJECTIVES: Fresh frozen human plasma is an important raw material in the production of coagulation factor concentrates used in patients with haemorrhagic disorders. The aim of the study was to determine how the handling of plasma influences the recovery of coagulation factor VIII activity (FVIII:C), i.e. the influence of time between donation and freezing, of the freezing time and of the ice front velocity. We also studied a tentative eutectic point in human plasma. MATERIALS AND METHODS: Aliquots of plasma from 12 different donors were kept at room temperature for 2, 4 and 6 h before start of freezing. We achieved fast freezing with a freezer that blows cooled air at a high velocity on the plasma containers. Freezing times were 0.5, 1, 4 and 24 h. Temperature was registered continuously during freezing. Plasma and NaCl solutions were frozen slowly to investigate the eutectic point. RESULTS: Storage at room temperature for 6 h caused a small but statistically significant decrease in FVIII:C. Slow freezing with programmed freezing times of 4 and 24 h caused a more pronounced drop in FVIII:C as compared to that of 30 and 60 min. We found no eutectic point in plasma or in plasma with addition of 2 % (w/v) NaCl. CONCLUSION: For an optimal yield of FVIII, freezing should start within 4 h after plasma donation. We propose the use of the term 'ice front velocity' instead of 'freezing speed', taking into consideration that the volume and shape of plasma containers may differ. We found only a marginal loss of FVIII:C when the ice front velocity was 26 mm/h or faster, but a significant loss when it was 9 mm/h or slower. We recommend freezing times of 60 min or shorter. We were not able to demonstrate any eutectic point in human plasma. We therefore recommend that the term eutectic point should not be used as a reference temperature in guidelines on plasma handling.
INTRODUCTION: One of the recommended criteria for the laboratory diagnosis of lupus anticoagulants (LA) is demonstration of inhibitory activity. This is confirmed by performing mixing tests with normal plasma, usually in a 1:1 ratio, and demonstrating persistence of an abnormal clotting time in the screening test with significant confirmatory test reduction. However, the mixing with normal plasma can dilute the antibodies to undetectable levels and generate apparent negative results. No guidelines or consensus exist in how to interpret mixing study results. PATIENTS AND METHODS: The present study assessed the 1:1 mixing study results from 600 patients with a thrombotic history positive for LA demonstrated in neat plasma by individual assays, or combinations, of dilute Russell's viper venom time, dilute activated partial thromboplastin time, activated seven lupus anticoagulant assay and Taipan snake venom time, plus confirmatory tests. Mixing tests were assessed initially using locally derived neat plasma reference ranges and subsequently with mixture specific ranges. RESULTS: The mixture specific ranges had lower upper limits. Of the total LA positive results, 32.5% were positive in the mixing studies when neat plasma reference ranges were applied, and a further 11.2% demonstrated LA activity when using the mixture specific ranges. The remaining 56.3% had been diluted such that they did not elevate the screening test above the upper limit of normal or generated minimal prolongation with an insignificant difference between the screen and confirmatory test result sufficient to confirm LA activity. CONCLUSIONS: The significant impact of the dilution effect in 1:1 mixing studies emphasises the limitations of mixing studies as a vehicle for confirmation of inhibition by LA antibodies.