A 'blind' study has been made to try to find out if it is possible to diagnose carriers of haemophilia. A group of 34 obligatory carriers of haemophilia were compared with 34 normal women. Levels of factor VIII activity, factor VIII-related antigen, factor V and ratio of factor VIII activity to factor VIII-related antigen were measured. In the carrier group the mean level of factor VIII activity and the mean level of the ratio of activity to antigen were each approximately half of those found in the normal women. The mean level of factor V was the same in both groups of women. By setting the lower limit of normal at the lowest level of the different factors found in the normal women, 12 out of 34 (35%) carriers could be distinguished on the basis of their factor VIII level alone; 24 out of 34 (71%) could be detected on the basis of the ratio of factor VIII activity to factor VIII related antigen and 25 out of 34 (73%) could be detected if both factor VIII activity and the ratio were taken into account. It is concluded that consideration of both the level of factor VIII activity and the ratio of factor VIII activity to factor VIII-related antigen is of some value in detecting carriers of haemophilia. The number of carriers detected (73%) in the present study is not as high as that found by other workers.

Summary. 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 during 23–26 November 1976 to investigate which of the possible sources of variation between laboratories were responsible. Participants from 16 British laboratories (nine using one‐stage assays and seven using two‐stage assays) performed a total of 273 valid assays using three freeze‐dried preparations of differing purity (a plasma, an intermediate and a high purity concentrate). The results of assay 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 corresponding 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 or citrate‐saline as opposed to haemophilic plasma for the initial dilution of concentrates did not affect the assay results.

Haemophilia B, or Christmas disease, is an inherited X-chromosome-linked bleeding disorder caused by a defect in clotting factor IX and occurs in about 1 in 30,000 males in the United Kingdom. Injection of factor IX concentrate obtained from blood donors allows most patients to be successfully managed. However, because of impurities in the factor IX concentrate presently in use, this treatment involves some risk of infection by blood-borne viruses such as non-A, non-B hepatitis and the virus causing acquired immune deficiency syndrome (AIDS). Because of the recent concern about the increasing incidence of AIDS amongst haemophiliacs, a factor IX preparation derived from a source other than blood is desirable. Here, we report that after introduction of human factor IX DNA clones into a rat hepatoma cell line using recombinant DNA methods, we were able to isolate small amounts of biologically active human factor IX.

A new assay of ristocetin co-factor has been developed which is based on platelet counting using a Coulter Counter. A modified method of washing and fixing platelets has also been devised to provide a suitable platelet preparation which can be used in this assay. These fixed platelets have consistently proved to be satisfactory and have given high levels of maximum percentage aggregation. They have been stored for periods up to 6 months without significant deterioration. The method of platelet counting is simple in operation and sensitive to relatively low levels of platelet aggregation. It is precise and seems to offer distinct advantages over existing methods.

A new method of factor VIII purification has been devised which involves chromatographic separation on aminohexyl-substituted agarose. Relatively large volumes of starting material can be processed compared to the volume of agarose employed and satisfactory yields are obtained. Factor-VIII-clotting activity is separated from the other related substances and resultant products appear to be stable. While separation of clotting activity occurs with relative ease, the antigen and ristocetin co-factor are hardly segregated, if at all. This provides a little more information about the interrelation of these substances. Results suggest that ion-exchange is involved in the mechanism of separation but additional hydrophobic or steric effects cannot be ruled out.