Interobserver and intraobserver variability using the Fuhrman grading system for renal cell carcinoma

Histologic grading of renal cell carcinoma has been shown to be second to staging in prognostic significance. A 4-tier grading scheme proposed by Fuhrman et al and based on nuclear features is the system used most frequently in North America. There are, however, very few studies in the literature assessing the interobserver variability for this system, and to our knowledge, none addressing intraobserver variability. To assess the interobserver and intraobserver agreement among 4 pathologists using the Fuhrman nuclear grading scheme for renal cell carcinoma. Representative hematoxylin-eosin-stained slides of 99 consecutive primary renal cell carcinoma cases diagnosed between 1994 and 1999 at St Joseph's Hospital, Hamilton, Ontario, were independently graded by 4 pathologists on 2 occasions with a minimum period of 3 months separating the 2 readings. Intraobserver kappa values ranged from 0.29 to 0.62 (mean = 0.45), and interobserver kappa values ranged from 0.19 to 0.38 and from 0.09 to 0.44 for the first and second rounds, respectively (combined mean kappa value = 0.29). When combining Fuhrman grades 1 and 2 as low-grade tumors and grades 3 and 4 as high-grade tumors, the intraobserver kappa values ranged from 0.4 to 0.64 (mean = 0.53) and interobserver kappa values ranged from 0.28 to 0.59 and from 0.26 to 0.58 for the first and second rounds, respectively (combined mean kappa value = 0.45). The admixture of 2 grades in the same tumor was observed in 53% of cases. We found only moderate intraobserver and interobserver agreement using the 4-grade Fuhrman scheme. After collapsing the diagnostic grades to 2, the intraobserver agreement changed from moderate to substantial. The collapsing of the 4-category Fuhrman grades into 2 categories is useful in improving intraobserver agreement.