1-Stage RVV-Based Factor X Assays

Russell's Viper Venom (RVV) activates factor X directly and in the presence of Factor V, prothrombin, Calcium and Phospholipid results in a fibrin clot.

The RVV assay is one of 5 assays for factor X but the PT and APTT-based assays are the most commonly performed.

 

Principles

The principle of the RVV Factor X is similar to that of the 1-stage PT-based Factor Assay. A series of dilutions of the reference and test plasma are made and clotted with RVV (see below).

 

Method

Reference or test plasma Dilutions: 1/10, 1/20, 1/140, 1/100
RVV + Platelet substitute Purchased commercially
0.025M Calcium Chloride  
FX deficient substrate plasma Purchased commercially

 

 

 

 

 

An aliquot of the FX deficient substrate plasma is mixed with an aliquot of the diluted reference or test plasma, incubated at 37°C for 30s and then the RVV-platelet substitute is added. 30s later clotting is initiated by the addition of 0.025M Calcium Chloride and the time to clot formation recorded. The results are plotted on Log-Log paper and the results derived as for the 1-stage PT-based assay.

 

Interpretation

Low factor X levels are seen in:

Congenital Factor X deficiency
In association with other clotting factor deficiencies in vitamin K deficiency and in patients on vitamin K antagonists
Liver disease
Amyloidosis due to absorption of FX onto the amyloid fibrils
Acquired factor inhibitors [rare]
Patients with deletions of chromosome 13 [chr13q] may have to combined FX and FVII deficiency as the genes for these two proteins are close together on the long arm of chromosome 13.

 

Reference Ranges

The reference ranges are identical to that of the PT-based FX assay

 

What Test Next?

See Intepretation of Results - which suggests what test(s) to do next.

 

Useful Links & References

  1. Choufani, E.B., Sanchorawala, V., Ernst, T., Quillen, K., Skinner, M., Wright, D.G. & Seldin, D.C. (2001) Acquired factor X deficiency in patients with amyloid light-chain amyloidosis: incidence, bleeding manifestations, and response to high-dose chemotherapy. Blood, 97, 1885-1887.
  2. Enjeti, A.K., Walsh, M. & Seldon, M. (2005) Spontaneous major bleeding in acquired factor X deficiency secondary to AL-amyloidosis. Haemophilia, 11, 535-538.
  3. Furie, B., Voo, L., McAdam, K.P. & Furie, B.C. (1981) Mechanism of factor X deficiency in systemic amyloidosis. N Engl J Med, 304, 827-830.
  4. Greipp, P.R., Kyle, R.A. & Bowie, E.J. (1981)Factor-X deficiency in amyloidosis: a critical review. Am J Hematol, 11, 443-450.
  5. Mulhare, P.E., Tracy, P.B., Golden, E.A., Branda, R.F. & Bovill, E.G. (1991) A case of acquired factor X deficiency with in vivo and in vitro evidence of inhibitor activity directed against factor X. Am J Clin Pathol, 96, 196-200.
  6. Peyvandi, F., Duga, S., Akhavan, S. & Mannucci, P.M. (2002) Rare coagulation deficiencies. Haemophilia, 8, 308-321.
  7. Uprichard, J. & Perry, D.J. (2002) Factor X deficiency. Blood Rev, 16, 97-110.
  8. Peyvandi, F., Menegatti, M., Santagostino, E., Akhavan, S., Uprichard, J., Perry, D.J., Perkins, S.J. & Mannucci, P.M. (2002) Gene mutations and three-dimensional structural analysis in 13 families with severe factor X deficiency. Br J Haematol, 117, 685-692

 

Data Interpretation

Click HERE to go to the Data Interpretation Exercises.