Biomedical subjects

Dawn Sands

Publications and source records attributed to Dawn Sands.

6 recordsLinked to original sources

PubMed2004

An International Standard for whole blood folate: evaluation of a lyophilised haemolysate in an international collaborative study.

Folate measurements, particularly for whole blood, show wide inter-laboratory and inter-methodology variability. This variability appears to be due in part to the lack of internationally accepted reference materials. A whole blood haemolysate, lyophilised in ampoules and designated 95/528, was therefore evaluated by 15 laboratories in five countries for its suitability as an International Standard (IS) for whole blood folate. The preparation was assayed using a variety of microbiological and protein-binding methodologies against local standards and calibrators. A consensus folate content was assigned to 95/528. The inclusion of three whole blood samples in the study with widely differing folate levels demonstrated a considerable reduction in inter-laboratory variability when the folate content of the samples was determined relative to the proposed IS 95/528 rather than to laboratories' local standards and calibrators. Accelerated degradation studies indicated that the folate content of 95/528 is stable when stored at -20 degrees C. On the basis of the results presented here, the World Health Organization Expert Committee on Biological Standardization established 95/528 as an IS for whole blood folate.

Centrifugation↗

PubMed2003

A multi-centre collaborative study on the potency estimation of ReFacto.

Seven laboratories estimated factor VIII coagulant activity in recombinant B-domain-deleted (ReFacto) and plasma-derived FVIII concentrates (Octonativ-M) using chromogenic methods relative to the WHO 6th International Standard FVIII Concentrate (WHO 6th IS), European Pharmacopoeia BRP#2 (EP#2) and the ReFacto Laboratory Standard (RLS). Significantly higher estimates were obtained for all batches of product when calculated relative to the RLS in comparison with estimates vs WHO 6th IS and EP#2. Mean estimates for two batches of ReFacto product vs the RLS were within 10% of the labelled potency whereas estimates vs WHO 6th IS and EP#2 ranged from 21 to 31% lower than the label. Conversely, mean estimates for Octonativ-M relative to WHO 6th IS and EP#2 were within 10% of the label whereas the mean estimate vs RLS was 117% of label. Mean estimates for the ReFacto product, vs the WHO 6th IS and EP#2, varied considerably between the different chromogenic kits whereas estimates vs the RLS showed good agreement between kits. Mean estimates for the RLS vs the WHO 6th IS (8.10 IU/vial) and the EP#2 (7.66 IU/vial) were lower than the assigned value of 9.4 IU/vial. The results are consistent with ReFacto and full-length FVIII responding differently to variations in assay methodology and also indicate that the assigned value on the RLS may be too high. Since this study the unitage on the RLS has been adjusted to effectively increase the amount of ReFacto in the product by 20%.

Chromogenic Compounds↗

PubMed2002

A stable lyophilized reagent for use in a potential reference assay for quantitation of anti-D in immunoglobulin products.

Quality control of anti-D immunoglobulins intended for in vivo clinical use requires in vitro assay of potency. A lyophilized biotinylated monoclonal anti-D (biotinylated Brad-5; 99/698) has been evaluated for its suitability to serve as a working reagent in a competitive enzyme-linked immunoassay (EIA) for anti-D quantitation. The reagent demonstrated acceptable stability in accelerated degradation tests and following reconstitution. Twelve international laboratories obtained comparable potencies for each of nine anti-D samples using 99/698 in a standardized assay procedure using erythrocytes fixed to microtitre plates. We also describe the use of trehalose for stabilization of dried erythrocyte-coated microtitre plates.

Antibodies, Monoclonal↗

PubMed2002

Coagulation and chromogenic assays of factor VIII activity: general aspects, standardization, and recommendations.

Factor VIII (FVIII) is assayed by one-stage and two-stage clotting methods and by chromogenic methods, although the chromogenic method has largely replaced the two-stage clotting assay. Clinical plasma samples are assayed mostly by one-stage assays, but most manufacturers of concentrates use the chromogenic method, which is more precise and is the reference method of the European Pharmacopoeia and the International Society on Thrombosis and Haemostasis (ISTH). For most plasma-derived concentrates, assays against the World Health Organization (WHO) concentrate standard give similar results with the one-stage and chromogenic methods, but for products produced by the "method M" monoclonal antibody process, the one-stage potency is 25 to 30% higher than the chromogenic potency. For full-length recombinant products assayed against a plasma-derived concentrate standard, one-stage potencies are about 10% lower than chromogenic potencies, but for the B-domain deleted recombinant product ReFacto, the discrepancy is larger-from 20 to 50%. These discrepancies emphasize the need for an international methodology for labeling of concentrates. In ex vivo assays of hemophilic plasmas after infusion of concentrates, large discrepancies are found among laboratories and with different assay methods when a plasma standard is used. In most studies, the chromogenic potencies are higher than the one-stage potencies, and the discrepancy is highest for recombinant products. This discrepancy can be largely eliminated by the use of concentrate standards, diluted in FVIII-deficient plasma, to assay postinfusion plasma samples.

Blood Coagulation Tests↗

PubMed2002

A collaborative study to establish the 3rd International Standard for tissue plasminogen activator.

An international collaborative study was organised to replace the 2nd International Standard (IS) for tissue plasminogen activator (tPA). The 2nd IS for tPA (86/670) was used to calibrate the replacement Standard, which was selected from two candidate materials included in the collaborative study. Participants were provided with five sets of four samples (A, B, C, D) and asked to use sample A (2nd IS, 86/670, 850 IU/ml) to determine the activity of B (86/624, approximately 850 IU/ml), C and D (coded duplicates of the same material, 98/714 approximately 11,000 IU/ml). A total of 14 laboratories returned results from Europe, USA, Japan and Australia, providing data from 60 independent assays. Four laboratories used a reference method based on a published monograph from the European Pharmacopoeia for Alteplase for Injection, 1998, and the remaining 10 used their own method. Fibrin was used as promoter of tPA activity by 12 out of the 14 laboratories, the remaining two used kits where fibrinogen fragments were the promoter. Data from this collaborative study and the previous study to establish the 2nd IS for tPA show that tPA from melanoma cells and recombinant tPA from CHO cells are both suitable materials as International Standards. It was agreed that sample C, D, recombinant tPA, 98/714, be established as the 3rd International Standard for tPA with a potency of 10,000 IU per ampoule, calculated as the mean value from laboratories using fibrin as a promoter of tPA activity. The standard was established by WHO in November 2000.

Animals↗

PubMed2002

Standardisation of von Willebrand Factor in therapeutic concentrates: calibration of the 1st International Standard for von Willebrand Factor concentrate (00/514).

An international study involving 26 laboratories assayed two candidate von Willebrand Factor (VWF) concentrates (B and C) for VWF:Antigen (VWF:Ag), VWF:Ristocetin Cofactor (VWF:RCo) and VWF:Collagen binding (VWF:CB) relative to the 4th International Standard Factor VIII/VWF Plasma (4th IS Plasma) (97/586). Estimates of VWF:Ag showed good agreement between different methods, for both candidates, and the overall combined means were 11.01 IU/ml with inter-laboratory variability (GCV) of 10.9% for candidate B and 14.01 IU/ml (GCV 11.8%) for candidate C. Estimates of VWF:RCo showed no significant difference between methods for both candidates and gave overall means of 9.38 IU/ml (GCV 23.7%) for candidate B and 10.19 IU/ml (GCV 24.4%) for candidate C. Prior to the calibration of the candidates for VWF:CB it was necessary to calibrate the 4th IS Plasma relative to local frozen normal plasma pools; there was good agreement between different collagen reagents and an overall mean of 0.83 IU per ampoule (GCV 11.8%) was assigned. In contrast, estimates of VWF:CB in both candidates showed large differences between collagen reagents with inter-laboratory GCV's of 40%. Candidate B (00/514) was established as the 1st International Standard von Willebrand Factor Concentrate by the WHO Expert Committee on Biological Standardisation in November 2001 with assigned values for VWF:Ag (11.0 IU/ampoule) and VWF:RCo (9.4 IU/ampoule). Large inter-laboratory variability of estimates precluded the assignment of a value for VWF:CB.

Calibration↗