Changes

Some specialised laboratories offer tests for specific clotting factors. Blood is required to be collected into a sodium citrate tube.

Some specialised laboratories offer tests for specific clotting factors. Blood is required to be collected into a sodium citrate tube.

===PIVKA===

===Proteins Induced by Vitamin K Antagonism Test===

The vitamin K-dependent coagulation factors (FII, FVII, FIX, FX) are produced in the liver as nonfunctional precursors. These precursors are activated, in the presence of vitamin K, by carboxylation of their glutamic acid residues. This is achieved with the aid of an enzyme called gamma glutamyl carboxylase. Carboxylation of these amino acid residues allows these coagulation factors to bind calcium, which is essential for the adhesion of these factors to platelet phospholipid (which is necessary for the coagulation cascade to proceed). The inactive precursors are stored in the microsomal system of the liver and are absent in the circulation in normal animals. In the absence of vitamin K, there is an increase in these precursors, which spill into the circulation, as well as a depletion of the functional activated coagulation factors. The inactive precursors that accumulate in the circulation are called Proteins Induced by Vitamin K Antagonism or Absence.

 

Factors II, VII, IX and X are produced in the liver as non-functional precursors which become activated by carboxylation of their glutamic acid residues in the presence of vitamin K. The inactive precursors are absent from the circulation of normal animals, as they are stored in the microsomal system of the liver. However, the absence of vitamin K results in an increase in these precursors, which spill into the circulation and become known as Proteins Induced by Vitamin K Antagonism. Concurrently, the levels of active factors II, VII, IX and X are depleted.

The PIVKA test or thrombotest is a modification of the prothrombin time. The test uses diluted plasma (which creates longer clotting times than the PT) and a specific thrombotest reagent, which is reported to be most sensitive to deficiencies in factor X. Although claims have been made in the veterinary literature that this test is sensitive to both an increase in PIVKAs (which are supposed to inhibit the reaction) as well as a decrease in the functional coagulation factors II, VII, and X (especially factors VII and X), there is no proof that PIVKAs actually inhibit the reaction. Therefore, the PIVKA test should be considered as a modified PT that detects deficiencies in factors II, VII, and X. Because the clotting times are longer than the PT, the test may be more sensitive than the PT for abnormalities in these factors, however this was not supported by a recent study measuring PIVKAs, PT and APTT in dogs with various hemostatic disorders. Furthermore, the test is only offered by certain laboratories and the turnaround time is longer than the PT, therefore measurement of PIVKAs offers no advantage over the PT. In human patients, the nonfunctional noncarboxylated coagulation proteins are measured specifically using immunologic tests.

The PIVKA test or thrombotest is a modification of the prothrombin time. The test uses diluted plasma (which creates longer clotting times than the PT) and a specific thrombotest reagent, which is reported to be most sensitive to deficiencies in factor X. Although claims have been made in the veterinary literature that this test is sensitive to both an increase in PIVKAs (which are supposed to inhibit the reaction) as well as a decrease in the functional coagulation factors II, VII, and X (especially factors VII and X), there is no proof that PIVKAs actually inhibit the reaction. Therefore, the PIVKA test should be considered as a modified PT that detects deficiencies in factors II, VII, and X. Because the clotting times are longer than the PT, the test may be more sensitive than the PT for abnormalities in these factors, however this was not supported by a recent study measuring PIVKAs, PT and APTT in dogs with various hemostatic disorders. Furthermore, the test is only offered by certain laboratories and the turnaround time is longer than the PT, therefore measurement of PIVKAs offers no advantage over the PT. In human patients, the nonfunctional noncarboxylated coagulation proteins are measured specifically using immunologic tests.