Working Group on Coagulation Secondary Standards

Chairman: Jane Lenahan
Saturday 06 August 2005
Harbourside Meeting Room 2

Use of SSC Lot #2 in QA exercises

Drs Brandt and Kitchen presented the results of EQA exercises in which SSC Lot #2 was tested as an anonymous sample. Results were encouraging in the good agreement between the mean values obtained and the values assigned to SSC Lot #2. One noticeable exception was the value for FVIII:C which differed from the assigned value and might be an indication that some manufacturers of calibrant plasmas have still not assimilated the re-alignment of the IU which occurred with the calibration of the WHO 4 th IS FVIII Plasma.

Status and calibration of SSC Lot #3

SSC Lot #3, consisting of 54,800 vials, was received from the manufacturer (Technoclone, Vienna ) by NIBSC in November 2003. Good progress has been made in the calibration of both existing and new parameters. Dr Hubbard reported on the calibration for Fibrinogen, FVII, Protein S and new parameters (FV and FXIII). Dr Gray reported on the calibration of FII, X, Antithrombin and a new parameter FXI; the calibration exercise for Protein C will be carried out over the next few months. Dr Kitchen reported on the calibration for FVIII, FIX and VWF, including the new parameter VWF:CB. Some responses from participants regarding the proposed assigned values are still outstanding. However, with the completion of the Protein C calibration in 2006 there will be a total of 19 assigned values on SSC Lot #3. It was agreed that the calibration reports should be circulated to the Executive Committee for consideration regarding formal assignment.

The calibration assays for SSC Lot #3 also included SSC Lot #2; in all cases there were no significant differences between the estimates for SSC Lot #2 obtained in the current study and those in the original calibration in 1999. This is a good indication of the continuity of the IU between Lots #2 and #3 and also supports the good stability of Lot #2.

Dr Declerck presented the results of an assessment into the feasibility of calibrating SSC Lot #3 for fibrinolytic parameters (tPA antigen, PAI-1 antigen, PAI-1 activity). Several laboratories estimated tPA antigen using different methods and standards and found reasonable agreement (with the exclusion of one outlier). Normalisation of the results relative to an NIBSC reference reagent was also encouraging in terms of inter-laboratory variability. A larger multi-centre study with a view towards formal calibration of the NIBSC reagent and SSC Lot #3 could be performed subject to approval by the Fibrinolysis sub-committee. Estimates for PAI-1 antigen were more variable and were not improved by normalisation relative to the WHO 1 st IS PAI – this may reflect differences between plasma PAI-1 and purified PA-1 used to spike the reference materials. This will be discussed further in the Fibrinolysis sub-committee. Estimates of PAI-1 activity were extremely variable and calibration was not considered feasible.

Dr Hubbard suggested that a more comprehensive “Instructions For Use” should be prepared for SSC Lot #3 to cover safety considerations, details of storage and reconstitution and bulk filling details. The label for Lot #3 was also discussed: it was agreed that the manufacturer should be consulted regarding the recommended storage temperature and that a decision on the expiry date should be made once the initial stability testing has been performed. There was overall agreement that the stability testing (accelerated degradation) should also include FV and FXI as well as FVII and FVIII.

Status of SSC Lot #2

Dr Hubbard reviewed the despatch of SSC Lot #2. Between May 2001 and June 2005 approximately 38,000 vials have been despatched leaving approximately 7,300 vials in stock. Use in proficiency studies by CAP and UK NEQAS accounted for over half of the total vials despatched. The stock level should be sufficient to maintain supply up to the labelled expiry date of June 2006.

Dr Hubbard presented the results of the stability testing of SSC Lot #2. The accelerated degradation study has been carried out over the last 6 years and is now completed. The residual potency (for FVII and FVIII) of vials stored at elevated temperatures has been measured at NIBSC and the Royal Hallamshire Hospital , Sheffield , UK (Dr Kitchen). The predicted % loss per year for vials stored at -20 °C did not exceed 0.011 % per year which indicates that SSC Lot #2 is extremely stable at the bulk storage temperature. The predicted stability at +20 and +37 °C supported the shipment of vials at ambient temperature. In addition, an objective real-time measure of the stability of vials stored at -20 °C was obtained by comparison with vials stored for 6 years at -70 °C; no difference in FVII or FVIII was found in assays performed by NIBSC and the Royal Hallamshire Hospital , Sheffield .

Joint Committee on Traceability for Laboratory Medicine

Dr Gray reviewed the need for SSC Lot #3 to be placed on the JCTLM database as an internationally certified reference material. The need to demonstrate commutability, with respect to the assay of normal plasma and/or patient plasma samples, as part of this process was also discussed. It was considered that the inclusion of SSC Lot #3 in QA surveys may satisfy this requirement. In accordance with Dr Gray’s recommendation Lot #3 will be nominated for inclusion on the JCTLM database.