Abstracts from the New England Section of the AUA 2020: A Virtual Experience

NE AUA 2020 Abstracts 56 Does CT scan after ultrasound change surgical planning for nephrolithiasis? Adam Ludvigson, MD , Piruz Motamedinia, MD Yale New Haven Hospital, New Haven, CT Introduction: Ultrasound (US) is often used to diagnose nephrolithiasis, but it is less accurate than CT scan, potentially affecting surgical plans. We examined how often obtaining a CT scan after US changed the indicated management of nephrolithiasis, to see if risk factors that determine inaccurate US scans could be identified. Materials &Methods: Approval was obtained through our institutional IRB. From those who presented to our health system over the past 3 years with suspected nephrolithiasis, we selected patients who had undergone a retroperitoneal US, and then a CT scan within 30 days. We recorded stone size and location for all studies. We recorded stone density and skin-to-stone distance for each CT scan. Using currentAUAguidelines, we determined the indicated procedure based on findings of each imaging study: extracorporeal shockwave lithotripsy (ESWL), ureteroscopy (URS), or percutaneous nephrolithotomy (PCNL). We used Minitab software to perform all statistical analysis, i.e. general linear models and two-tailed Student’s t-tests. Results: 305 patients met inclusion criteria. Of these, the CT scan changed the indicated procedure 108 times (35.4%). 26 US studies indicated ESWL; CT changed 19 of these (73%). 129 US studies indicated URS; CT changed 62 of these (48%). 24 US studies suggested PCNL; CT changed 9 of these (37.5%). Using CT as the gold standard, 18 US studies were false positive for stones (sensitivity=0.72). 51 US studies were false negative for stones (specificity = 0.86).Average body mass index (BMI) was significantly lower in the patients with a false positive US as compared to those with a true positive US (26.59 versus 29.13 kg/m 2 , t(24)=2.33,p=0.029).Whencomparingpatientswhohadtheir indicatedprocedure changed by the CT scan to those who did not, there were no significant differences in age, BMI, or skin-to-stone distance. However, those who had their procedure changed had significantly lower density stones (566.1 versus 747.5 HU, t(154) = 2.92, p = 0.004). When patients were examined in subgroups based on what their indicated procedure was before and after the CT scan, there were also no significant differences based on age, BMI, or skin-to-stone distance. There was a significant difference based on HU, with stone density explaining 22.88% of the variation (F(11,154) = 4.15, p&lt;0.001). Conclusions: US has many advantages over CT, but cannot always be used in place of it. Our study demonstrates that a CT scan changes the indicated stone treatment in more than 1/3 of cases, and that lower-density stones are a risk factor for inaccurate US findings. US should be used with particular caution in those with a history of low-density stone types, and for ESWL surgical planning. 57 Association of Prior Pregnancy with 24-hour Urine Composition and Stone Risk Vivian Paredes Bhushan, MS 1 , Marie-Therese Valovska, MD 1 , Vernon M. Pais, Jr., MD 2 1 Dartmouth Geisel School of Medicine, Hanover, NH; 2 Dartmouth-Hitchcock Medical Center, Lebanon, NH Introduction: Pregnancy isassociatedwith increased lifetimeprevalenceofnephrolithiasis. Duringpregnancy,purportedchanges inurinarymilieu includehypercalciuriaandalkaline urine, whichmay predispose to calciumphosphate urolithiasis. Postpartum, it is unknown whether the cumulative number of pregnancies is associated with increased risk of these findings and calciumphosphate stone formation. We studied the effect of prior pregnancies on the urinary milieu and stone composition in a cohort of female stone formers. Materials & Methods: With IRB approval, we performed a single-center retrospective reviewofstonepatients treatedbetween2007and2017.We identifiednon-cystinuric, living female patients with complete 24-hour urinalyses and stone analyses who consented to a pregnancy history questionnaire. Linear regression was used to assess the association of pregnancy with urinary calcium, calcium phosphate supersaturation (SSCaP), and pH, comparing nongravid (G0) and previously gravid women. Pure stones were assigned to their respective category. Mixed stones were assigned to the category corresponding to their predominant crystal species. We additionally categorized stones containing > 10% calcium phosphate as “calcium phosphate-containing stones”. Age, body mass index (BMI), and diabetes were adjusted for in the multivariate analysis. Results: Of 116 who met inclusion criteria, 22 (19%) were G0 and 97 (81%) were previously gravid. Of those previously gravid, 15 (12.9%) were primigravid (G1), 26 (22.4%) secundigravid (G2), and 53 (45.7%) had three or more pregnancies (G3+). Mean age was 54.3 years, and did not differ significantly by history of pregnancy (p = 0.9). Mean years since last pregnancy was 24.6. Mean BMI at time of 24 hour urine was 29.6 kg/m 2 . Previously gravid women were more likely to exhibit hypercalciuria than G0 women (50% vs. 22.7%, p < 0.05). Mean urine calcium was increased in G3+ women compared to G0 women (211.9 mg vs. 153.2 mg, p < 0.05). On multivariate analysis, both SSCaP and urine calcium remained elevated in G3+ compared to G0 women (+0.049 and +49 mg/d, respectively, p < 0.05). Prior gravidity did not impart significant effect onmost recent urine pH. There was no difference in the odds of calcium oxalate stone formation among G0 women and previously gravid women, across all number of pregnancies. There was no difference observed in the odds of predominantly calcium phosphate stone formation of greater than 50% composition among G0 women and previously gravidwomen. However, comparedwith G3+women, nulligravids were significantly less likely to have any calcium phosphate-containing stones (OR: 0.296; p = 0.034; 95%CI [0.096-0.912]). Conclusions: Women with multiple pregnancies were more likely than G0 women to have hypercalciuria and elevated SSCaP, even decades after their last pregnancy. While these findings are suggestive of lasting effects, there was no proclivity in the formation of predominantly calcium phosphate stones, suggesting that pregnancy is only one of many factors contributing to nephrolithiasis. Acute Changes in 24 Hour Lithogenic Urine Measures Intra and Peri Partum Eileen Brandes, MD , Zita Ficko, MD, Elizabeth Johnson, MD, Vernon Pais, Jr., MD Dartmouth-Hitchcock Medical Center, Lebanon, NH Introduction: Urinary lithogenic changes during pregnancy have been hypothesized to contribute to both stone formation during pregnancy as well as long term increased stone prevalence in multigravid women. However, while short-term lithogenic changes during pregnancy have been postulated, such changes have never been demonstrated in a prospective fashion controlling for diet. Wide inter-person variation in food consumption can account for dramatic differences in 24 hour urinalyses and thus introduces potential confounding. We thus sought to define intrapartum 24 hour urine values and to assess the acute short term changes after completion of the pregnancy >= 6 weeks post-partum. To address potential dietary confounding and thus elucidate those changes intrinsic to the physiology of pregnancy, we utilized a standardized formula to control for dietary intake. Materials &Methods: IRB approval was obtained for this prospective study. Womenwith singleton pregnancy presenting to the obstetrical department were offered participation. Those with gestational diabetes were excluded. Metabolic needs were assessed by an obstetrical dietitian and standardized diet was calculated based on each woman’s metabolic requirements. The standardized diet consisted of boost plus, boost breeze and unlimited water. Vitamin supplements were held. Collections were obtained during the third trimester and follow-up urine was collected at 6 weeks or greater postpartum. Subjects remained on the controlled diet for 48 hours – the 24 hours preceding urine collection and continued for the 24 hours of the urine collection. Statistical analysis were performed in STATA using T-test. Results: Of the twenty participants currently enrolled in this study, twelve have submitted a pre- and post-partum 24 hour urine collection. Post-partum collections analyzed in this study were done at any point after delivery, regardless of breast feeding and menstrual status. It was noted that there was no significant difference in known dietary-related factors of urinary volume, sodium, sulfate and urea nitrogen. Urinary calcium was found to be 302.5 pre-partum and 125.2 post-partum (p = 0.001). Urinary pHwas 6.59 pre-partum and 5.93 post-partum (p < 0.001). Urinary super saturation of calcium phosphate (ssCaP) was 2.1 pre-partum and 0.7 post-partum (p < 0.0001). Conclusions: Hypercalciuria and alkaline urine are observed acutely during pregnancy. By implementing a standardized formula diet, for the first time, we have demonstrated these changes are independent of self-selected diet and thus intrinsic to pregnancy. Abnormally elevated urinary super saturation of calcium phosphate during pregnancy further suggests that these changes may have clinical importance. 55 25 Scientific Session VI: Stones II/ Basic Science