Specific factor assays

Specific factor assays are variations on the APTT or PT tests. In the APTT and PT, dilutions of the patient s plasma are made into a deficient, or depleted, substrate plasma. The assays are then performed in the usual way. The clotting times are compared with those obtained from dilutions of pooled normal plasma, commonly 1 10, 1 20, 1 50, and 1 100. A graph of the logarithm of the clotting time (y axis) versus the logarithm of the concentration as percentage of normal x axis) is used to determine the amount of the factor activity in the patient s plasma. The normal pooled plasma is conventionally assigned a value of 100% activity. Many variations exist for specific factor assays, e.g., the venom of Vipera russellii and phospholipids may be substituted for thromboplastin in a PT-like assay. An enzyme in Russell s viper venom rapidly and relatively specifically activates factor X. In conjunction with a factor X-deficient substrate plasma, this provides a specific factor X assay. 

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Quantification was developed by measuring the relationship between the shortening of the clotting time of the plasma from the patient with the bleeding disorder (deficient plasma) and the amount of normal plasma added to the deficient plasma. This approach remains the basis for specific factor assays however, the deficient plasmas are depleted of individual factors by immunoprecipitation and separation of the antibody-factor complex from the plasma. 

Specific Factor Assays Factor VIII Factor IX Other Factors Evaluation of the functional concentration (activity) of individual factors, specificity created by using specific factor deficient plasmas. Commonly performed as an aPTT-like assay Sensitivity is to the factor missing from the particular deficient plasma Estimation of the activity level of a particular factor Differences may be observed between deficient plasmas from individuals with hereditary deficiencies and immunodepleted plasmas... 

A young African-American male patient is brought to you because of a hemarthrosis sustained after he twisted his knee while running. His PT is normal, but his APTT is 51 s (normal 20-32 s). Mixing equal volumes of the patient s plasma and normal plasma shortens the APTT to 25 s. Specific factor assays show a normal factor IX activity, but a factor VIII activity of 25% of that in pooled normal plasma. Why was his PT normal What else, prior to the factor IX and VIII assay results, might have been responsible for the prolonged APTT ... 

V Mucosal tract bleeding Prolonged PT and aPTT Normal thrombin time Specific factor V assay... 

VII Mucosal tract, joint and normal aPTT Prolonged PT Specific factor VII assay... 

XIII Umbilical cord, intracranial, and joint bleeding recurrent miscarriages, impaired wound healing Normal PT, aPTT, thrombin time, bleeding time Specific factor XIII assay... 

S. H. Bartelmez and E. R. Stanley, Synergism between hemopoietic growth factors (HGFs) detected by their effects on cells bearing receptors for a lineage specific HGF assay of hemopoietin-1, 7.C eT/./ A/sjo/ 122, 370-378 (1985). 

Decisions surrounding specific HTS assay technologies will take into consideration factors including pharmacological relevance, HTS compatibility, follow-up strategy, and costs, among... 

Specific heparin assays employ either exogenous thrombin or Factor Xa. Exogenous antithrombin may also be added to ensure that only heparin is measured... 

Coagulation Specific coagulation factor assay, FPA, D-dimer, Fi+a, PAC-1,S-12,TAT PTT (nonactivated), PT, TT, plasma fibrinogen, FDP... 

For determination of isozyme levels of the mammalian synthetase, two procedures have been developed. The first involves adsorption of the acidic isozyme on DEAE cellulose or adsorption of the basic isozyme on cellulose phosphate (27-29). The amount of activity that is not bound can be measured and the bound activity can be eluted and determined by methods described above. Matsuda et al. (27) have also utilized an antibody against the basic isozyme to precipitate that isozyme and measure the acidic isozyme activity remaining. Development of specific radioimmune assays for each isozyme will allow more detailed studies on factors that affect the level of each isozyme in specific tissues. 

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