Agreement of point-of-care prothrombin and activated partial thromboplastin time in dogs with a reference laboratory

To determine the agreement, sensitivity, specificity and accuracy of prothrombin (PT) and activated partial thromboplastin time (aPTT) using the point-of-care analyser SCA2000™ with IDEXX Coag Dx™ cartridges against a reference laboratory (STAGO Start 4®) in canine blood.

Citrated blood samples from 47 dogs were submitted for PT and aPTT measurements. The STAGO was taken as the gold standard and sensitivity, specificity and accuracy were calculated. Agreement between the IDEXX and STAGO test results was compared using Bland-Altman analysis and Passing-Bablok regression.

The IDEXX cartridges had a sensitivity of 92% (95% confidence interval (CI) 62-100%) and specificity of 98% (95% CI 87-100%; n = 54 samples). aPTT sensitivity was 100% (95% CI 63-100%) and specificity was 47% (95% CI 30-65%, n = 42 samples). The accuracy of IDEXX cartridges compared with the STAGO Start 4 was 96% (95% CI 91-100%) for PT and 57% (95% CI 42-72%) for aPTT. Agreement was moderate-good for PT measurements within the reference range (RR). Agreement was poor for PT measurements outside of the RR and for aPTT measurements within and outside the RR. The bias between measurements from the two machines was inconsistent.

PT results from the point-of-care IDEXX were generally reliable for diagnosing or excluding a coagulopathy. The aPTT IDEXX sensitivity was excellent but the specificity was poor. Bland-Altman analysis and Passing-Bablok regression indicated an inconsistent bias between the two measurements and one measurement cannot be reliably converted to the other.