Predicting differential renal function using computerized tomography measurements of renal parenchymal area.

PURPOSE

We evaluated any correlation between measured renal parenchymal area on computerized tomography and differential function on (99m)technetium-mercaptoacetyltriglycine renal scan to ascertain whether computerized tomography measurements could predict differential renal function.

MATERIALS AND METHODS

Between 2005 and 2007 we identified 111 patients who underwent computerized tomography and renal scan. Average renal parenchymal thickness was calculated by measurements made at the upper and lower poles of each kidney. The product of average renal parenchymal thickness and renal length was calculated bilaterally and the ratio of parenchymal area was compared to the differential shown on renal scan.

RESULTS

The average difference between predicted and observed renal function was 4.73% (Pearson's correlation coefficient 0.959). Patients with positive urine cultures at renal scan were compared to the other 89. The average functional difference was 6.54% vs 4.28% (Pearson's correlation 0.955 vs 0.965, p = 0.0045). The 89 uninfected patients were then compared based on contrast vs noncontrast computerized tomography and obstructed vs unobstructed renal units. No statistical difference was found with contrast administration. When compared based on evidence of obstruction, unobstructed kidneys resulted in a lower Pearson correlation (0.743 vs 0.975) but they had a statistically significant average functional difference in favor of unobstructed units (3.28% vs 5.10%, p = 0.0036). No difference was found in the obstructed group with prior drain placement.

CONCLUSIONS

Differential renal parenchymal area measured by computerized tomography strongly correlates with differential function on renal scintigraphy and it may obviate the need for nuclear renal scan in some circumstances.