Influence of Sample Predilution on the Sensitivity of Prothrombin Time in Feline Plasma

Abstract

The prothrombin time (PT) is measured in feline plasma usually by means of a method that has been optimized for measurements in human plasma (standard test). In the present study the sensitivity of this test was investigated in comparison to a modified PT using a human placental thromboplastin. In the modified test, 100 fl sample predilution (1 :5, 1 : 10, and 1 :20) were incubated with 100 pl of a human fibrinogen solution (2 g/l) until 100 pl Ca-thromboplastin was added. When measured in 31 samples with a reduced, and 22 samples with an increased activity of the coagulation factors 11, V, VII and/or X the modified test showed an increased sensitivity as well as a correlation between PT and the changes in single factor activity which was distinctly closer compared to the standard test. The highest sensitivity was produced by a 1 : 10 or 1 :20 sample dilution. A test procedure modified in this way, is thus, a more reliable screening test for the extrinsic system in cats and should be used for routine diagnostics.

Proteins Invoked by Vitamin K Absence and Clotting Times in Clinically Ill Cats

“…The influence of sample predilution on increasing the sensitivity of routinely used prothrombin assays in feline plasma has previously been shown. 9 The low frequency of prolonged PT or APTT clotting times was not unexpected based on the authors' clinical experience. These tests are notoriously discordant with clinical observations in human beings and companion animals.…”

“…However, human assay systems can be optimized in several ways to improve test sensitivity. 9,10,15 It is widely acknowledged that the risk of in vivo bleeding is not reliably discerned from routine in vitro hemostatic assessments. [2][3][4][5]17 The apparent heightened sensitivity of the PIVKA clotting time determined by the Thrombotest reagent may be able to identify cats with bleeding tendencies while clinically asymptomatic.…”

“…Routinely determined PT and APTT using assay systems manufactured for humans often lack sensitivity for detection of coagulopathies in the dog and cat as the reagent balance is usually not optimized for species other than humans. 9,10 Long-term experience with the dismal sensitivity of routinely used coagulation tests prompted a preliminary investigation of an alternative coagulation system that measures the PT but is exquisitely sensitive to the accumulation of inactive forms of the vitamin K-dependent coagulants (Thrombotest a ). 11 In this assay, accumulated procoagulants of the vitamin K-dependent clotting factors act as substrate analogues delaying thrombin activation.…”

Sedative, cardiovascular, haematologic and biochemical effects of four different drug combinations administered intramuscularly in cats

“…Blood coagulation tests were performed with the coagulation analyzer Amax Destiny plus (Trinity Biotech, Germany) using the clotting technique (ball coagulometer). Prothrombin time (PT) was measured with the reagent Thromborel (Siemens Healthcare) following a modified test: 25 μL of diluted citrated plasma (1:20 dilution) was incubated with 25 μL fibrinogen for 2 minutes at 37 °C and the coagulation was induced by addition of 25 μL Thromborel S (Mischke et al. 1996).…”

Laboratory evaluation and interpretation of haemostasis in small animals

“…In specialised laboratories, the use of an optimised test (e.g., 100 µl 1:20 diluted sample, 100 µl fibrinogen solution [to guarantee an adequate fibrin clot formation], incubation for 2 minutes, 100 µl Ca-thromboplastin reagent) is preferable to the standard test for use in dogs and cats (Mischke et al, 1996;Mischke and Nolte, 1997). Apart from the modified test, commercial PT test modifications such as Hepato Quick or Normotest are suitable screening tests of the extrinsic system in dogs and cats .…”