The conditions for which the geometric mean method revealed a more accurate calculation of relative renal function in 99mTc-DMSA scintigraphy.

Aims: (1) To compare the results of calculating relative renal function (RRF) by using only posterior images (POST) with the geometric mean (GM) through both anterior and posterior imaging on dimercaptosuccinic acid (DMSA) scintigraphy. (2) To determine whether there was an age-related difference between them and whether some renal pathologies or asymmetrical renal function cause an error in the RRF calculation by using posterior images only.

Methods: Eight hundred and ninety-one DMSA scans were studied retrospectively. The patients were divided into five age groups: group I, < or =2 years; group II, >2 to < or =5 years; group III, >5 to < or =10 years; group IV, >10 to < or =18 years; and group V, >18 years. The RRF of the right kidney (RKF) was calculated from the POST and GM counts. The differences between RKFGM and RKFPOST were calculated in all the patients.

Results: Among the 891 patients, nine had malrotated or malpositioned kidneys, 373 had renal pathologies of pyelonephritis, hydronephrosis, cortical scarring and atrophy, 247 had asymmetrically functioning kidneys and 509 had normal kidneys. When the patients were analysed according to different age groups, significant differences were found between all groups (P<0.05) except groups I-II and IV-V (P>0.05) with the F-test. The clinically meaningful RRF variance (> or =5% difference between two methods) rate differed significantly between groups I, II and III, and groups IV and V (chi-squared test, P<0.05). In patients aged < or =10 years, a clinically meaningful RRF variance (> or =5%) rate was significantly higher in the groups with pathological or asymmetrically low (< or =40% RRF) functioning kidneys than in the groups without pathological or asymmetrically low functioning kidneys, respectively (P<0.05).

Conclusions: According to our findings, the calculation of RRF using the GM method differs significantly from that using posterior images. Calculation of the GM can effectively correct the RRF measurement not in only adults, but also in the patient population musical #10 years of age. In addition, a significant correction can be made in patients aged musical #10 years who have a renal pathology or an asymmetrically low functioning kidney.