Percent of Tracer Clearance at 40 Minutes in MAG3 Renal Scans Is More Sensitive Than T1/2for Symptomatic Ureteropelvic Junction Obstruction.
To increase the diagnostic sensitivity of standard MAG3 diuretic renal scans for ureteropelvic junction obstruction (UPJO) by exploring the utility of an alternative measurement P40,the percentage of maximal tracer counts present at 40 minutes.



Patients with strong clinical and anatomic evidence for UPJO may have a normal T1/2, making definitive diagnosis difficult. We reviewed the charts of 142 consecutive patients who underwent successful laparoscopic or robotic-assisted laparoscopic pyeloplasty for UPJO between 2005 and 2015. Both pre- and postoperative renal scan images were available for 37 symptomatic patients with primary unilateral UPJO and 2 kidneys. We defined P40as the percentage of maximal tracer counts present at 40 minutes. We identified the upper limit of normal (97.5th percentile, +2SD) for P40using the preoperative renal scans from the unaffected kidney. We compared the sensitivity of P40to T1/2to identify symptomatic UPJO.



In our cohort, 51% of symptomatic patients (n = 19) had a normal T1/2(median 8.9 minutes; interquartile range: 7.5 minutes) and 49% (n = 18) had an abnormal T1/2(median: 40 minutes; interquartile range: 0 minute). None of the patients had an abnormal P40on their unaffected kidney. All patients with an abnormal T1/2also had an abnormal P40. P40increased the sensitivity of the renal scan from 49% (n = 18 of 37) to 73% (n = 27 of 37) when compared to T1/2. The majority of patients (95%) demonstrated an improvement in P40 after pyeloplasty.



P40markedly increases the sensitivity of a renal scan for diagnosing symptomatic UPJO and may be another valuable marker in addition to T1/2to document functional improvement in drainage after pyeloplasty.
Scott Department of Urology, Baylor College of Medicine, Houston, TX; Department of Urology, Jena University Hospital, Friedrich-Schiller University, Jena, Germany.
Friedrich-Carl
FC
von Rundstedt
Scott Department of Urology, Baylor College of Medicine, Houston, TX.
Jason M
JM
Scovell
Scott Department of Urology, Baylor College of Medicine, Houston, TX; Department of Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles, CA.
Shelly X
SX
Bian
Scott Department of Urology, Baylor College of Medicine, Houston, TX; Department of Urology, St. George Hospital, Kogarah, New South Wales, Australia.
Dominic
D
Lee
Scott Department of Urology, Baylor College of Medicine, Houston, TX.
Wesley A
WA
Mayer
Scott Department of Urology, Baylor College of Medicine, Houston, TX. Electronic address: link@bcm.edu.
Richard E
RE
Link
D000328:Adult; D004232:Diuretics / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D007677:Kidney Function Tests / Q000379:methods; D010535:Laparoscopy / Q000379:methods; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D011184:Postoperative Period; D011849:Radioactive Tracers; D019651:Plastic Surgery Procedures / Q000009:adverse effects / Q000379:methods; D065667:Renal Elimination / Q000502:physiology; D065287:Robotic Surgical Procedures / Q000379:methods; D012680:Sensitivity and Specificity; D063189:Symptom Assessment; D014055:Tomography, Emission-Computed / Q000379:methods*; D014517:Ureteral Obstruction / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D013519:Urogenital Surgical Procedures / Q000009:adverse effects / Q000379:methods
D004232:Diuretics; D011849:Radioactive Tracers