Association Between Specimen Length and Number of Sections and Diagnostic Yield of Temporal Artery Biopsy for Giant Cell Arteritis

Objective: To investigate the association between specimen length and number of sections evaluated and the diagnostic yield of temporal artery biopsy (TAB) for giant cell arteritis (GCA). Methods: A pathologist reviewed all TABs performed for suspected GCA between January 1991 and December 2012. The blocks of all the inadequate and negative biopsy specimens were recut, and further slides at deeper levels were stained with hematoxylin and eosin in order to avoid missing inflammatory changes. Results: In total, findings from 662 TABs were included in the study (71% female; mean age 73.2 years). A total of 427 TAB specimens (65%) were classified as negative, and 235 (35%) were classified as positive for GCA. Compared to those with negative TAB results, patients with positive TAB results were older and more frequently female. There was no difference in postfixation TAB specimen length between TAB specimens negative and positive for GCA (mean 6.5 mm versus 6.9 mm; P = 0.068). Cuts of additional biopsy sections revealed inflammation at deeper levels in 26 of 408 TAB specimens (6.4%) originally reported as uninflamed. The inflamed section was the second in 14 TAB specimens, the third in 9 specimens, and the fourth in 3 specimens. Piecewise logistic regression identified 5 mm as the TAB specimen length change point for diagnostic sensitivity. Compared to a TAB specimen length of <5 mm, the age- and sex-adjusted odds ratio for positive TAB results in samples ≥5 mm long was 1.5 (95% confidence interval 1.0–2.0), P = 0.032. Conclusion: A postfixation TAB specimen length of at least 5 mm should be sufficient to make a histologic diagnosis of GCA. In order not to miss inflammatory changes, at least 3 further sections at deeper levels should be evaluated in all negative TAB specimens.