Lyophilized plasma as an assay standard for facfactor VIII: calibration and control with fresh plasma samples

An improved procedure for accurate assays of factor VIII

An improved one-stage method for accurate assays of factor VIII combines highly reproducible end points with elimination of temporal drift and of subjective factors involved in graphic analysis. Activated deficient plasma substrate (ADPS) is used as a single reagent for parallel tests. The assays can be performed manually or, with much greater precision, on an 8-channel coagulation meter of new design in which end points are recorded automatically and depend on an abrupt clearing of agitated cloudy suspensions. The coagulation time readings are reproducible to 0.5%. Factor VIII levels are read off a standard table or computed from a general equation which is readily programmable on a pocket calculator and is valid over a wide range of concentrations, including very low plasma levels.

Classification of von Willebrand's disease

The classification of von Willebrand's disease should be based primarily on the mode of inheritance: thus, the main division would between autosomal dominant and autosomal recessive types. Phenotypic subdivisions within these major types may then be possible. A subgroup of the dominant type seems to be well defined by increased electrophoretic mobility of the VIII-related antigen.

Factor VIII coagulant activity in an African population in relation to a recognized standard

The normal range of factor VIII coagulant activity (derived from log potency ratio) in some sections of the Nigerian population has been established at 0.65--5.55 iu/ml with a geometric mean of 1.90 iu/ml. This was determined against an acceptable standard (MRC Human 68/413 with activity o.66 iu/ml). The distribution of the potency ratio was log normal. The level was not affected by age or an abnormal haemoglobin (Hb A + S or A + C). The mean activity in females was significantly higher than the mean value in male subjects. With the use of a stable standard, our results show that the conclusions of some previous studies in respect of some of the parameters such as population distribution but which did not use a recognized standard, were valid. Within the age limits of our subjects, age did not affect the population level of factor VIII coagulant activity.

A computer program for the analysis of parallel-line bioassays of clotting factors

An interactive computer program for the analysis of clotting factor assays is described. The program provides potency estimates against a standard, and will compare the observed and expected responses of a treated patient. Tests for validity of curve fitting are provided, with a number of optional transforms. If asked, the program will provide the user with a list of valid commands at any given step, and will identify certain errors in input.

The value of age- and sex-matched controls for coagulation studies

Several coagulation parameters and plasminogen levels were studied in 80 normal people divided into eight paired and sex-matched age groups: prepubertal children, postpubertal children, young adults, and adults over 50. The data indicate that factor-VII and -IX activities increase with age, with a cluster of lower activity for children and higher activity for adults. Factor-VIII levels appear to decrease with age, although this effect could be due to greater anxiety in the pre- and postpubertal children at the time of venipuncture. The adults showed no significant change in factor-VIII activity with age, but partial data indicate that factor-VIII levels are higher in adults with blood group A than those with blood group O. The age-related changes in factor-VII, -IX, and possibly -VIII activities did not vary between sexes. By contrast, plasminogen increased strikingly with age in males and decreased with age in females. With fibrinogen, a similar effect was found for adults, though not for the entire population. These findings indicate the importance of using appropriate age- and sex-matched controls for coagulation and plasminogen assays, especially in patients with mild inherited or acquired coagulation disorders.