Use of error grid analysis to evaluate acceptability of a point of care prothrombin time meter.
BACKGROUND
Statistical methods (linear regression, correlation analysis, etc.) are frequently employed in comparing methods in the central laboratory (CL). Assessing acceptability of point of care testing (POCT) equipment, however, is more difficult because statistically significant biases may not have an impact on clinical care. We showed how error grid (EG) analysis can be used to evaluate POCT PT INR with the CL.


METHODS
We compared results from 103 patients seen in an anti-coagulation clinic that were on Coumadin maintenance therapy using fingerstick samples for POCT (Roche CoaguChek XS and S) and citrated venous blood samples for CL (Stago STAR). To compare clinical acceptability of results we developed an EG with zones A, B, C and D.


RESULTS
Using 2nd order polynomial equation analysis, POCT results highly correlate with the CL for CoaguChek XS (R(2)=0. 955) and CoaguChek S (R(2)=0. 93), respectively but does not indicate if POCT results are clinically interchangeable with the CL. Using EG it is readily apparent which levels can be considered clinically identical to the CL despite analytical bias.


CONCLUSIONS
We have demonstrated the usefulness of EG in determining acceptability of POCT PT INR testing and how it can be used to determine cut-offs where differences in POCT results may impact clinical care.
Petersen
John R
JR
University of Texas Medical Branch, Galveston, Texas 77555-0551, United States. jrpeters@utmb.edu
Vonmarensdorf
Hans M
HM
Weiss
Heidi L
HL
Elghetany
M Tarek
MT
D001774:Blood Chemical Analysis / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D019934:International Normalized Ratio; D019095:Point-of-Care Systems / Q000592:standards; D011516:Prothrombin / Q000032:analysis*; D015203:Reproducibility of Results; D013997:Time Factors
D011516:Prothrombin