An International Collaborative Assay of Factor VIII Clotting Activity

1978 ◽  
Vol 40 (02) ◽  
pp. 260-271 ◽  
Author(s):  
T W Barrowcliffe ◽  
T B L Kirkwood
Keyword(s):  
Factor Viii ◽  
World Health ◽  
Expert Committee ◽  
Two Stage ◽  
International Standard ◽  
One Stage ◽  
Normal Plasma ◽  
Freeze Dried ◽  
The Mean ◽  
International Collaborative

SummaryAn International Collaborative Study was organised to replace the first International Standard for factor VIII. A freeze-dried concentrate, 73/552, and a freeze-dried plasma, 75/510, were assayed against the International Standard, and also compared to fresh normal plasma and local standards.In assays of the concentrate 73/552 against the first I.S. the mean potency was 1.14 i.u./ ampoule and there was no significant difference between one-stage and two-stage methods. When assayed against average fresh normal plasma, the potency was 1.05 “normal plasma units” per ampoule. It was agreed by the participants that the potency of 73/552 be regarded as the mean of these two figures, i.e. 1.10 i. u./ampoule.In assays of the freeze-dried plasma, 75/510, against the first I.S. the mean potency was 0. 68 i. u./ampoule, but the one-stage assays gave significantly higher potencies (mean 0.74 1. u./ampoule) than the two-stage assays (mean 0.59 i. u./ampoule). The same trend was also seen in the fresh normal plasmas, and in the local plasma standards. This finding has important implications for the standardisation of factor VIII.Stability studies on the concentrate 73/552 gave a predicted loss of 0.02% per year at – 20° C. All participants agreed that the material was suitable to serve as an International Standard, and at the 26th meeting of the Expert Committee on Biological Standardisation of the World Health Organization, the material in ampoules coded 73/552 was established as the 2nd International Standard for factor VIII, with a potency of 1.10 i. u./ampoule.

Standardization of Factor VIII – IV. Establishment of the 3rd International Standard for Factor VIII: C Concentrate

1983 ◽  
Vol 50 (03) ◽  
pp. 697-702 ◽  
Author(s):  
T W Barrowcliffe ◽  
A D Curtis ◽  
D P Thomas
Keyword(s):  
Factor Viii ◽  
High Purity ◽  
Collaborative Study ◽  
World Health ◽  
Current Standard ◽  
Two Stage ◽  
International Standard ◽  
One Stage ◽  
The One ◽  
Health Organization

SummaryAn international collaborative study was carried out to establish a replacement for the current (2nd) international standard for Factor VIII: C, concentrate. Twenty-six laboratories took part, of which 17 performed one-stage assays, three performed two-stage assays and six used both methods. The proposed new standard, an intermediate purity concentrate, was assayed against the current standard, against a high-purity concentrate and against an International Reference Plasma, coded 80/511, previously calibrated against fresh normal plasma.Assays of the proposed new standard against the current standard gave a mean potency of 3.89 iu/ampoule, with good agreement between laboratories and between one-stage and two- stage assays. There was also no difference between assay methods in the comparison of high-purity and intermediate purity concentrates. In the comparison of the proposed standard with the plasma reference preparation, the overall mean potency was 4.03 iu/ampoule, but there were substantial differences between laboratories, and the two-stage method gave significantly higher results than the one stage method. Of the technical variables in the one-stage method, only the activation time with one reagent appeared to have any influence on the results of this comparison of concentrate against plasma.Accelerated degradation studies showed that the proposed standard is very stable. With the agreement of the participants, the material, in ampoules coded 80/556, has been established by the World Health Organization as the 3rd International Standard for Factor VIII :C, Concentrate, with an assigned potency of 3.9 iu/ampoule.

A Collaborative Study to Establish the 6th International Standard for Factor VIII Concentrate

2001 ◽  
Vol 85 (06) ◽  
pp. 1071-1078 ◽  
Author(s):  
A. B. Heath ◽  
T. W. Barrowcliffe ◽  
S. Raut
Keyword(s):  
Factor Viii ◽  
Collaborative Study ◽  
World Health Organisation ◽  
World Health ◽  
Assay Method ◽  
Expert Committee ◽  
International Standard ◽  
One Stage ◽  
The One ◽  
Good Agreement

SummaryA study was carried out to replace the 5th WHO International Standard (IS) for factor VIII concentrate, because of depletion of stocks. Two candidate concentrates (X and Y) were assayed as potential replacements against the 5th IS for FVIII concentrate, in a collaborative study involving 33 laboratories. Collaborators were asked to use the ISTH/SSC recommendations, including pre-dilution of concentrates in FVIII deficient plasma in their assays. Several laboratories performed more than one assay method and altogether there were 21 sets of assays with the one-stage method, 6 with the two-stage method and 26 with the chromogenic method. There was good agreement between laboratories using each method for the comparison of concentrates X and Y against the 5th IS, but the overall potencies by one-stage and chromogenic methods each differed by approximately 5% from the overall mean, with the chromogenic potency approximately 10% higher than the one-stage. Inter-laboratory agreement was slightly better for concentrate Y than X, and stability studies indicated that Y was more stable than X. After considering all the information, together with comments from participants and from the FVIII/FIX Subcommittee of the ISTH/SSC, candidate Y (NIBSC code [97/616]), was proposed and accepted in October, 1998, by the Expert Committee on Biological Standardisation of the World Health Organisation to be the 6th International Standard for Factor VIII Concentrate with an assigned potency of 8.5 IU/ampoule.

scholarly journals An International Collaborative Study of Factor VIII

1977 ◽  
Author(s):  
T. W. Barrowcliffe ◽  
T. B. L. Kirkwood
Keyword(s):  
Factor Viii ◽  
Collaborative Study ◽  
Expert Committee ◽  
International Standard ◽  
Normal Plasma ◽  
Collaborative Studies ◽  
Freeze Dried ◽  
Significant Difference ◽  
Assay Methods ◽  
The Common

A collaborative assay was organised to assess the suitability of a replacement for the first International Standard for Factor VIII. Coded samples of a freeze-dried concentrate (proposed 2nd I. S.), the 1st I.S., and a freeze-dried plasma were assayed by 15 laboratories against fresh normal plasma and local standards. Ten laboratories performed 1-stage assays and five 2-stage.The proposed 2nd I. S. had a mean potency of 1.14 International Units per ampoule by direct assay against the 1st I. S.., with no significant difference between one- and two-stage assays. When assayed against a large number of individual normal plasmas, the proposed standard was equivalent to 1.05 ml “average normal plasma” per ampoule. In assays of the common freeze-dried plasma against the 1st I. S., there was a significant difference between assay methods, the 1-stage assays giving higher results for the plasma than the 2-stage. This difference between assay methods confirms results from other collaborative studies, and it seems likely that the 2-stage method is detecting relatively more activity in the concentrate standards.It was agreed by the participants that the proposed material is suitable, in terms of stability and comparability with other materials, to serve as the 2nd International Standard for Factor VIII. The standard was established by WHO at the 28th meeting of the Expert Committee on Biological Standards, with a potency of 1.1 IU per ampoule.

A Collaborative Study Designed to Establish the 4th International Standard for Heparin

1984 ◽  
Vol 52 (02) ◽  
pp. 148-153 ◽  
Author(s):  
D P Thomas ◽  
A D Curtis ◽  
T W Barrowcliffe
Keyword(s):  
Collaborative Study ◽  
International Standard ◽  
Thrombin Inhibition ◽  
Freeze Dried ◽  
Assay Methods ◽  
The Mean ◽  
International Collaborative ◽  
International Collaborative Study

SummaryAn international collaborative study, in which 22 laboratories participated, was carried out to establish a replacement for the International Standard for Heparin. A total of 248 assays were analyzed, including APTT, thrombin inhibition and anti-Xa assays, as well as pharmacopoeial assays. Overall, there was less than 5% difference in the mean potency estimates of the candidate preparations, by all assay methods. The freeze-dried preparation 82/502 demonstrated the closest parallelism by bioassay to the existing standard and was established by WHO as the 4th International Standard for Heparin, with an assigned unitage of 1780 i.u. per ampoule.

scholarly journals Identification of Sources of Inter-Laboratory Variation in Factor VIII Assay

1977 ◽  
Author(s):  
T.B.L. Kirkwood ◽  
C.R. Rizza ◽  
T.J. Snape ◽  
I. Rhymes ◽  
D.E.G. Austen
Keyword(s):  
Factor Viii ◽  
Systematic Difference ◽  
Normal System ◽  
Two Stage ◽  
Initial Dilution ◽  
One Stage ◽  
Collaborative Studies ◽  
Freeze Dried ◽  
Sources Of Variation ◽  
The One

A repeated finding of national and international collaborative studies of standard Factor VIII preparations has been that systematic differences exist between laboratories in their measurement of the relative activities of the same pairs of Factor VIII preparations.A workshop meeting was held at the Oxford Haemophilia Centre (England) during 23rd-26th November 1976 to investigate which of the possible sources of variation between laboratories were responsible. Participants from 16 British laboratories (9 one-stage, 7 two-stage) performed a total of 273 assays using three freeze-dried preparations of differing purity (a plasma, an intermediate and a high purity concentrate). The results of assays with each participant using their normal system established that, if the participants were a representative cross-section, approximately one-third of one-stage laboratories would show a systematic difference from the overall mean of at least 16%, with a similar figure for the two-stage laboratories of 9%. Various features of the assay systems were then modified in a controlled series of experiments. The results showed conclusively that i) differences between reagents accounted for most of the variation between laboratories and, ii) the two-stage assays were, on average, detecting relatively more activity in the more purified preparations than the one-stage assays. The results also suggested that the use of buffer as opposed to haemophilic plasma for the initial dilution of concentrates did not affect the assay results.

Comparative Investigations on Factor VIII Assays

1975 ◽  
Author(s):  
R. Pflugshaupt ◽  
S. Moser ◽  
K. Züger ◽  
R. Bütler
Keyword(s):  
Factor Viii ◽  
High Activity ◽  
Hemophilia A ◽  
Statistical Evaluation ◽  
Two Stage ◽  
One Stage ◽  
Normal Plasma ◽  
Calibration Curves ◽  
Factor Viii Concentrates

Six one stage methods and one two stage method were tested for precision and reproducibility. With each method twenty calibration curves of normal plasma and two lots of Factor VIII concentrates were established. Statistical evaluation revealed only minor differences. Neither one of the methods was optimal for both the physiological-pathological region and the region of high activity preparations.Three selected methods were tested in vivo for accuracy: nine patients with hemophilia A were treated with equal amounts of Factor VIII concentrates or kryoprecipitates respectively. The methods showed different activities for preparations as well as for patient’s plasma. The discrepancy between measured and expected recovery differed for each method.

An International Standard for holotranscobalamin (holoTC): international collaborative study to assign a holoTC value to the International Standard for vitamin B12 and serum folate

2016 ◽  
Vol 54 (9) ◽  
pp. 1467-1472 ◽  
Author(s):  
Susan J. Thorpe ◽  
Peter Rigsby ◽  
Graham Roberts ◽  
Anne Lee ◽  
Malcolm Hamilton ◽  
...  
Keyword(s):  
Vitamin B12 ◽  
Collaborative Study ◽  
World Health ◽  
Serum Folate ◽  
Expert Committee ◽  
Specific Marker ◽  
Serum Samples ◽  
International Standard ◽  
International Collaborative ◽  
International Collaborative Study

AbstractBackground:Investigation of possible B12 and folate deficiencies requires measurement of these vitamins in serum. There is evidence that holotranscobalamin (holoTC), the active portion of B12 available to cells, is a more specific marker of early B12 deficiency than total B12. The availability of immunoassays for holoTC prompted an international collaborative study to assign a holoTC value to the World Health Organization (WHO) 1st International Standard (IS) for vitamin B12 and serum folate, 03/178.Methods:The IS, 03/178, and three serum samples with different holoTC levels were assayed by 12 laboratories in eight countries using manual and automated immunoassays for holoTC; one laboratory additionally performed an in-house assay. Fourteen sets of data were analysed.Results:Overall, the IS, 03/178, and the three serum samples demonstrated assay linearity and parallelism. An overall geometric mean (GM) holoTC value of 106.8 pmol/L was obtained for 03/178, with an inter-laboratory geometric coefficient of variation (GCV) of 10.5%. There was a reduction in inter-laboratory variability when the holoTC levels in the serum samples were determined relative to the IS with an assigned holoTC value rather than to the assays’ calibration. Accelerated degradation studies showed that 03/178 was sufficiently stable to serve as an IS for holoTC.Conclusions:The WHO Expert Committee on Biological Standardization endorsed the proposal to assign a holoTC value of 107 pmol/L to 03/178, corresponding to 0.107 pmol per ampoule, for use as the 1st IS for vitamin B12, serum folate, and holoTC.

International Collaborative Study for the Establishment of the Second International Reference Preparation of Plasmin

1983 ◽  
Vol 50 (03) ◽  
pp. 645-649 ◽  
Author(s):  
P J Gaffney ◽  
M V Mussett
Keyword(s):  
Collaborative Study ◽  
World Health ◽  
Expert Committee ◽  
Glycerol Solution ◽  
International Reference ◽  
Freeze Dried ◽  
Reference Preparation ◽  
International Collaborative ◽  
International Collaborative Study ◽  
Second International

SummaryAn international collaborative study involving seven laboratories was undertaken to assess the suitability of a freeze- dried preparation of human plasmin to replace the current International Reference Preparation (IRP) for plasmin. Chromogenic and fibrinolytic assays were used by all participating laboratories to assess the potencies of the Proposed International Reference Preparation (PIRP) and two other freeze-dried plasmins, one of human and one of porcine originThe data suggest that the PIRP is a more suitable standard for plasmin than the IRP in that the former binds to fibrin whereas only 50% of the latter binds. The PIRP compared well to other plasmin preparations and the potency assays were independent of the assay procedure and substrate used. Degradation studies indicated that the PIRP was far more stable than the glycerol solution of the IRP, surviving for 12 months at 37° C with no significant loss in either amidolytic or fibrinolytic activity. The International Committee for Thrombosis and Haemostasis (Bergamo, 1982) has recommended the use of this material as a standard and it has been established by the Expert Committee on Biological Standardization of the World Health Organization as the second International Reference Preparation for Plasmin with a defined potency of 10 International Units of Plasmin per ampoule.

Study of a Proposed International Standard for Blood Coagulation Factor IX

1976 ◽  
Vol 35 (01) ◽  
pp. 222-236 ◽  
Author(s):  
Milica Brozović ◽  
T. B. L Kirkwood ◽  
Iris Robertson
Keyword(s):  
Collaborative Study ◽  
Factor Ix ◽  
World Health ◽  
Systematic Effect ◽  
Good Precision ◽  
Confidence Limits ◽  
Potency Ratio ◽  
International Standard ◽  
Normal Plasma ◽  
Freeze Dried

SummaryAn International Collaborative Study was organized to establish a standard for factor IX. Two freeze-dried concentrate preparations, C1 and C2, and one freeze-dried plasma P were compared with each other, with fresh normal plasmas and with local standards in 13 laboratories. One of the concentrate preparations (C1) contained heparin and this gave rise to non-parallel assays in laboratories testing concentrate C1 in dilutions containing more than 0.05 i.u. of heparin per ml.Assays of factor IX showed good precision for both plasma and concentrate in all laboratories; no systematic effect of method, operator or day of assay was detected.The plasma preparation P and the concentrate preparation C2 were compared with 59 individual fresh normal plasma samples, and a mean potency ratio of 0.78 (95% confidence Hmits 0.73-0.84) for plasma and 5.62 (95 % confidence limits 5.13-6.16) for the concentrate C2 obtained. Only 21 estimates of concentrate C1 in terms of fresh plasma were obtained giving a mean potency ratio of 3.85 (95% confidence limits 1.87—7.92).The estimated loss of potency for freeze-dried plasma stored at — 20° C is approximately 0.4% per year. The concentrate C2 is apparently more stable and only very small losses occurred even at higher storage temperatures.All participants agreed that the preparation C2 would be suitable to serve as an International Standard for factor IX; they also agreed that the figure assigned for the unitage should be based on the number of ml of ‘average fresh normal plasma’ estimated to contain the factor IX activity of one ampoule of the preparation. It is proposed to recommend to the World Health Organization that the preparation of factor IX concentrate C2, in ampoules coded 72/32, be considered for establishment as the International Standard for factor IX, and that the international unit for factor IX be assigned on the basis of 5.62 units per ampoule of this preparation.

A Collaborative Study to Establish the 2nd International Standard for Fibrinogen, Plasma

2000 ◽  
Vol 84 (08) ◽  
pp. 258-262 ◽  
Author(s):  
C. M. Whitton ◽  
D. Sands ◽  
P. J. Gaffney ◽  
A. R. Hubbard
Keyword(s):  
Geometric Mean ◽  
Collaborative Study ◽  
World Health Organisation ◽  
World Health ◽  
Expert Committee ◽  
Washington Dc ◽  
International Standard ◽  
Freeze Dried ◽  
Assay Methods ◽  
Almost All

SummaryAn International Collaborative Study involving 12 laboratories in 7 different countries was undertaken in order to replace the 1st International Standard (IS) for Fibrinogen, Plasma (89/644). The candidate replacement standard was the ampouled and freeze-dried residue of solvent/detergent treated plasma and was calibrated as coded duplicates (A and B) versus the 1st IS Fibrinogen, Plasma by automated Clauss assay and by a recommended clot collection (gravimetric) assay. This latter method had been used to calibrate the 1st IS Fibrinogen, Plasma.Comparing the ratios of the potency estimates of sample A to sample B (the coded duplicates), all of the laboratories obtained a ratio within 5% of the expected value of 1.0 by automated Clauss assay, which suggests that the laboratories were able to perform this assay well. Scrutiny of the data obtained from the gravimetric assays revealed that in almost all cases the results were invalid. The results of these assays are included in this report but clearly should be treated with caution and indeed produced significantly lower mean estimates of potency than the other assay methods. The overall geometric mean of all estimates of potency of the proposed 2nd IS Fibrinogen, Plasma (98/612) is 2.19 mg/ampoule by the automated Clauss assay. These data have been presented to the Fibrinogen Sub-Committee of the Standardisation and Scientific Committee (SSC) of the International Society on Thrombosis and Haemostasis (ISTH) (Washington, DC, August 1999), which recommended the establishment of 98/612 as the 2nd IS Fibrinogen, Plasma. This report has been presented to the Expert Committee on Biological Standardisation of the World Health Organisation (ECBS-WHO) at their 1999 session and 98/612 was established as the 2nd IS Fibrinogen, Plasma with a potency of 2.2 mg/ ampoule.

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