Frozen section diagnosis in donor liver biopsies: observer variation of semiquantitative and quantitative steatosis assessment

Donor livers are not generally accepted for liver transplantation if intraoperative frozen section histology on wedge biopsies provides evidence for more severe steatosis. In this reliability study, assessment of steatosis in donor liver biopsies by different approaches (frozen sections vs. paraffin sections; macrovesicular steatosis vs. microvesicular steatosis), different observers, and different evaluation methods (conventional microscopy vs. point grid analysis on digital microphotographs) was compared. One hundred twenty consecutive donor liver biopsies were investigated. Intraoperative diagnosis was made on hematoxylin and eosin (H&E)-stained frozen sections. The residual portion of each biopsy was analyzed later on H&E-, diastase-resistant PAS-, and Elastica van Gieson-stained paraffin sections. Microvesicular steatosis and macrovesicular steatosis were classified semiquantitatively into 5 % steps. Additionally, point grid counting was applied on ten digital microphotographs per slide. The values for steatosis revealed a wide range of data between 0 and 70 or 85 % (mean values, 12.0-18.3 %), considering all types of specimens. The results of the two observers were highly correlated for macrovesicular steatosis (r a parts per thousand yenaEuro parts per thousand 0.925) and for microvesicular steatosis (r a parts per thousand yenaEuro parts per thousand 0.880). The values for macrovesicular and microvesicular steatosis, however, showed poor correlation (r a parts per thousand currency signaEuro parts per thousand 0.581). The rate of agreement between the two observers ranged between 84.2 and 95.8 % (kappa, 0.763-0.937), depending on the threshold setting. For point grid analysis, significantly lower mean values and ranges for both types of steatosis compared to conventional histopathology were found (p < 0.001). Comparing the results of point grid analysis with those of conventional histopathology, a relatively loose correlation was found (r, 0.581-0.779). Intraoperative histology remains a reliable and highly relevant method for the assessment of steatosis in liver donor grafts. It represents one important component in the decision-finding whether or not a donor liver should be accepted and should possibly be combined with results of preoperative computed tomography imaging. Considering our data, macrovesicular and microvesicular steatosis should be analyzed separately due to the limited correlation between them.