Evaluation of STA-NeoPTimal, an extraction thromboplastin reagent with ISI close to 1

The prothrombin time (PT) is the most requested test to investigate patients with congenital or acquired coagulopathies or to monitor oral anticoagulant therapy. However, thromboplastins can show markedly different responsiveness to the defects induced by vitamin K antagonist (VKA) therapy and are thus characterized by their ISI (International Sensitivity Index). INR results are optimal for patients under VKA but for patients screened for other reasons expressing PT results as ratio can be more appropriate. As it is very difficult to define the PT results reporting unit from the PT testing request, it would be ideal to use a thromboplastin with ISI = 1. The study aims to compare our reference PT reagent with two candidate thromboplastins with ISI close to 1.

We compared 3 different thromplastins: two rabbit brain extracted based reagents (STA-Neoplastine CI Plus, with ISI = 1.26, routinely used in our laboratory and STA-NeoPTimal with ISI = 1.01) and a recombinant thromboplastin (STA-Neoplastine R with ISI = 0.97). The comparison was done on 175 samples: 75 from individuals without coagulation defects and 100 from patients under VKA.

STA-NeoPTimal and STA-Neoplastine R well correlate to our reference, STA-Neoplastine CI Plus: regression equations are y = 1.186x-0.1351, r²  = .9454 and y = 1.1432x-0.1554, r²  = .9951, respectively. The lowest bias on INR results was obtained with STA-NeoPTimal reagent (interval: -0.7/+0.4).

We conclude that STA-NeoPTimal can be used in the laboratory as it gives results comparable to those obtained with STA-Neoplastine CI Plus. Besides, thanks to its ISI = 1, it guarantees reporting a PT ratio equal to INR which avoids errors.