No signiﬁcant difference was noted between the HU values of calcium oxalate and calcium phosphate stones, and thus they were analyzed collectively as “calcium stones.” When the HU values of calcium , uric acid, struvite, and cystine stones were compared, the overlap of ranges precluded accurate identiﬁcation, and the mean HU values were not signiﬁcantly different from one another. There was less overlap noted when comparing the HU densities of the stones studied, and no noncalcium stone had an HU density greater than 76 HU/mm. Using one-way analysis of variance, signiﬁcant differences were noted between the mean HU density of calcium (105 6 43) and uric acid (50 6 24) stones (P 5 0.006). A trend toward signiﬁcance was found between the mean HU density of the calcium and struvite stones (53 6 28, P 5 0.073). No signiﬁcant differences were found among the other stones.
HU density (HU value was divided by each stone’s largest transverse diameter in millimeters) compared with the HU value alone better characterized differences in radiodensities among urinary stones; calcium stones can be distinguished from uric acid stones on the basis of this value. However, neither the HU density nor the mean HU value was able to identify urinary stones in vivo. UROLOGY 58: 170–173, 2001. © 2001, Elsevier Science Inc.