Preparation of 'contact product' as a reagent for coagulation tests

Chromatography of the VIII/vWF complex on dextran sulphate sepharose

The applicability of Dextran Sulphate (DS) agarose in the purification of the VIII/vWf complex from cryoprecipitate was investigated. The elution profiles indicate high affinity of the VIII/vWf complex for the matrix. With application of combined salt/pH gradients good resolution of VIII/vWf from most of the applied proteins can be achieved. VIII/vWf normally elutes as a single component (70-90% vWf:Ag and vWf:RCo) with modest yields of factor VIII (30-40%) VIII:C and 50-70% VIII:Ag) providing calcium ions are present. Addition of L-lysine, Histidine and Arginine (all 1.0M) inhibit binding of proteins to the matrix. Alternatively, higher yields of VIII:C can be obtained (80% VIII:C and 100% VIII:Ag) by the application of L-lysine gradients (0-0.6M) but with loss of resolution from Fn and slight dissociation of VIII:C from vWf:Ag.

An artificial 'haemophilic' plasma for one-stage factor-VIII assay

An 'artificial' plasma for one-stage factor-VIII assays is made by incubating human plasma with EDTA, to destroy factor VIII, and afterwards removing the anticoagulant by dialysis. Bovine factor V is then added to a given level. In the assay, contact activation is controlled by adding contact product. It was confirmed that factor-VIII activity was destroyed and that the EDTA was freely dialysable. The fibrinogen in the treated plasma clotted normally with thrombin. Likely variation in the factor-V activity was found not to be critical. The concentration of fibrinogen and other factors was adequate. Variation between batches was small. The artificial plasma yielded assay results closely comparable to haemophilic plasma in samples with factor-VIII activities in the range 0.01--20.0 iu/ml; the mean results in the artificial system were estimated to be 0.997 x those in haemophilic plasma, with a 95% confidence interval of 0.901--1.103. Biological variability in individual assays was smaller in the artificial system than when haemophilic plasma was used. Instability at the bench was more often detected in the artificial system than in haemophilic plasma assays, but the effect was eliminated from the results by obtaining duplicated readings in a balanced order.

Factor-VIII activity and antigen, platelet count and biochemical changes after adrenoceptor stimulation

Adrenaline, isoprenaline and salbutamol were administered by intravenous infusion to human subjects. Isoprenaline was covered with practolol in an attempt to reduce the unpleasantness of the circulatory effects. Changes were recorded in pulse rate and blood pressure, and in blood levels of factors V, VIII, X, XI, and XII, platelet count, lactate, pyruvate, potassium and free fatty acids. Factor VIII was studied by clotting assays, by reactions with two rabbit antisera and two human antibodies, and by desulphated agarose chromatography. At the rate at which they were adiminstered, all three drugs increased the pulse rate by 20-40 beats/min. Factor VIII rose c. 2.5 X with adrenaline but only c. 1.5 X with isoprenaline and salbutamol; but other clotting factors did not alter. Chromatography provided no evidence of a change in the size of the molecule carrying factor-VIII clotting activity. The rate of clearance of the heightened plasma activity could not be shown to differ from that of "ordinary" factor VIII infused into haemophiliacs. The platelet count rose after adrenaline, fell after salbutamol and did not change significantly after isoprenaline. Among the biochemical responses, the only significant difference between the drugs was that lactate rose after adrenaline and salbutamol but did not change after isoprenaline. The rise in factor-VIII clotting activity after adrenaline is considered to represent a real increase in blood concentration, presumably by release of additional factor VIII from stores. The evidence suggests that this could be classified as a beta2 effect; and that the quantity which can be released is unrelated to the current plasma level. The rise in platelet count produced by adrenaline may be the resultant of an alpha-mediated rise due to contraction of the exchangeable splenic pool and a beta2-mediated fall, the alpha effect predominating.

Bleeding from self-administration of phenindione: a detailed case study

A young woman presented with a 2 year history of a severe bleeding disorder and marked deficiencies in all four vitamin-K-dependent factors. Metabolic studies with tracer doses of tritium-labelled vitamin K1 suggested that the patient might be taking an oral anticoagulant; and subsequently her plasma was found to contain a substance identical to phenindione in its spectrophotometric and chromatographic properties. The half-disappearance times of factors II, IX, X were measured after the administration of a concentrate of these factors and were found to conform with published figures. The concentrate controlled the patient's excessive bruising and prolonged skin and gingival bleeding. It would therefore seem that factor VII may not be essential in reversal of the bleeding disorder induced by anticoagulant overdose.

Simple screening tests for the diagnosis of isolated clotting factor defects. With special reference to 'contact factor' defects

Reagents may be prepared from normal plasma and used with the prothrombin time and partial thromboplastin time tests to distinguish isolated defects of factors I, II, VII, VIII, IX, X, XI, or XII.