TECHNETIUM-99M-MAG3 RENAL STUDIES IN SPINAL-CORD INJURY PATIENTS - NORMAL RANGE, REPRODUCIBILITY, AND CHANGE AS A FUNCTION OF DURATION AND LEVEL OF INJURY

The normal range, reproducibility, and change as a function of duratio n and level of injury for Tc-99m-MAG3 renal studies were quantitated i n spinal cord injury (SCI) patients. METHODS: Five SCI patients withou t evidence of renal disease in each of four groups: less than 2 months , 2-12 months, 1-2 years, and greater than 2 years from time of injury , were each studied twice. There were at least two patients with parap legia and two with tetraplegia in each group. Renal clearance (camera based method), percent function in each kidney, time of peak renal par enchymal activity, and half time of parenchmal activity following the peak were evaluated. The peak and half times were determined with regi ons of interest (ROIs) over the entire kidney and over just the cortex . All results were compared to normal ranges previously established in normal subjects of the same age range using the same methodology. RES ULTS: Renal clearance in the less than 2 month SCI patients was not si gnificantly different from normal subjects in either paraplegic or in tetraplegic individuals. However, clearance in tetraplegics was increa sed by 28.5% at 2-12 month, increased by 50.6% at 1-2 years, and decre ased by 25.9% at greater than 2 years compared to normal subjects (all P<0.02). Clearance in those with paraplegia showed a similar, but les s marked, trend (P=NS). The time of peak parenchymal activity when mea sured with cortical ROIs did not vary among patient groups or level of injury, but was increased compared to normal subjects (P<0.05). The p ercent function in each kidney and half time following the peak were s ymmetrical, did not differ among patient groups or with level of injur y, and did not differ from normal subjects. The parenchymal peak time was significantly shorter with cortical rather than renal ROIs in all patient groups (P<0.05). In serial studies in the same patient the per cent standard deviation in total renal clearance was less than between single studies in different patients, but the decrease was significan t for only the right kidney (P<0.03), and the decrease was not as grea t as in normal subjects. In addition, the percent standard deviation f or percent function in each kidney was significantly less than the per cent standard deviations in single studies (P<0.02). There were no sig nificant differences between intra- and interpatient studies for any o ther parameter. CONCLUSION: We conclude that: (1) renal clearance meas ured with Tc-99m-MAG3 in tetraplegic patients increases significantly during the first 2 years following injury and decreases significantly thereafter; there is a similar, but much less marked, trend in paraple gics, (2) parenchymal peak times with cortical ROIs occur later for SC I patients than for normal subjects, and (3) there is more intrapatien t variation in total renal clearance and percent renal clearance on a side in SCI patients than in normal subjects suggesting that it may be harder to study SCI patients reproducibly. These findings should be t aken into account when performing and interpreting Tc-99m-MAG3 renal s tudies in SCI patients.