Coaguchek XS vs Lab vs i-Stat machine

[pellicle]

Hi

was just reading this and thought I'd post my notes as I read. It may be of interest to anyone worried about the accuracy of their devices (or just curious)


Accuracy of Capillary Whole Blood International Normalized Ratio on the CoaguChek S, CoaguChek XS, and i-STAT 1 Point-of-Care Analyzers
American Society for Clinical Pathology
2008;130:88-92

From the Abstract

We evaluated the accuracy of capillary whole blood international normalized ratio (INR) on the CoaguChek S ... XS .. and i-STAT 1 ... point-of-care (POC) analyzers
... compared with venous plasma INRs determined by a reference laboratory method.
...
Overall agreement between POC and laboratory plasma INR was very good,...
...
More than 90% of results on the CoaguChek XS and i-STAT 1 and 88% of CoaguChek S results were within 0.4 INR units of the reference laboratory method.

General notes I made while reading:

The CoaguChek XS and i-STAT 1 demonstrated greater accuracy than the CoaguChek S as measured by the number of results that differed by more than 0.5 INR units from the reference method.

The i-STAT and CoaguChek XS measure clotting by electrochemical current detection following activation of blood clotting by recombinant thromboplastin.

For the CoaguChek XS instrument, the median bias between capillary whole blood and laboratory plasma INRs was 0.0 INR units, with 1 of 48 capillary whole blood specimens differing by more than 0.5 INR units from the reference method.

scatter plot of INR variances

The difference in median bias between the CoaguChek S (0.0 INR units) and i-STAT (–0.1 INR units) was not statistically significant (P > .05).
...
only 8 of 48 warfarin dosages would have changed based on the CoaguChek XS whole blood INR result compared with the plasma INR result.

not bad ... would have been nice if they'd mentioned by how much the dose varied.

There were fewer patients with capillary whole blood INRs differing by more than 0.5 INR units from the reference method on the CoaguChek XS (1 of 48) and i-STAT 1 (1 of 50) devices compared with the CoaguChek S (8 of 98).

There were fewer patients with capillary whole blood INRs differing by more than 0.5 INR units from the reference method on the CoaguChek XS (1 of 48) and i-STAT 1 (1 of 50) devices compared with the CoaguChek S (8 of 98). Thus, the newer POC INR devices should allow for more accurate assessment of anticoagulation status,

Overall there seem to be few studies which follow the same procedure and the article mentions this. Makes for broader meta-analysis (comparison of eachothers results) of other studies difficult.

we will now resume our normal programme