Concordance among pathologists in the second Cardiac Allograft Rejection Gene Expression Observational Study (CARGO II).

Background: There has been no large evaluation of the ISHLT 2004 acute cellular rejection grading scheme for heart graft endomyocardial biopsy specimens (EMBs).
Methods: We evaluated agreement within the CARGO II pathology panel and between the panel (acting by majority) and the collaborating centers (treated as a single entity), regarding the ISHLT grades of 937 EMBs (with all grades ≥2R merged because of small numbers).
Results: Overall all-grade agreement was almost 71% both within the panel and between the panel and the collaborating centers but, in both cases, was largely because of agreement on grade 0: for the average pair of pathologists, fewer than a third of the EMBs assigned grade ≥2R by at least one were assigned this grade by both.
Conclusion: The 2004 revision has done little to improve agreement on the higher ISHLT grades. An EMB grade ≥2R is not by itself sufficient as a basis for clinical decisions or as a research criterion. Steps should be taken toward greater uniformity in EMB grading, and efforts should be made to replace the ISHLT classification with diagnostic criteria--EMB based or otherwise--that correspond better with the pathophysiology of the transplanted heart.