- Kidney Stones
Clinical Assistant Professor, Medicine - Nephrology
Honors & Awards
Ben J. Lipps Research Fellowship Award, American Society of Nephrology (2017-2019)
K23 Mentored Patient-Oriented Research Career Development Award, National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health (2022-2027)
Board Certification: American Board of Internal Medicine, Nephrology (2019)
MS, Stanford University, Epidemiology and Clinical Research (2019)
Fellowship: Stanford University Nephrology Fellowship (2018) CA
Board Certification: American Board of Internal Medicine, Internal Medicine (2017)
Residency: UCSD Internal Medicine Residency (2016) CA
Medical Education: UCLA David Geffen School Of Medicine Registrar (2013) CA
Bachelor of Science, Caltech (2009)
- National Imaging Trends for Suspected Urinary Stone Disease in the Emergency Department. JAMA internal medicine 2022
Osteoporosis, Fractures, and Bone Mineral Density Screening in Veterans With Kidney Stone Disease.
Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research
Whether a link exists between kidney stone disease and osteoporosis or fractures remains an open question. In this retrospective cohort study, we sought to determine the prevalence of osteoporosis and fractures and rate of bone mineral density screening by dual-energy X-ray absorptiometry (DXA) in patients with kidney stone disease. We examined nationwide data from the Veterans Health Administration and identified 531,431 patients with kidney stone disease between 2007 and 2015. Nearly 1 in 4 patients (23.6%, 95% confidence interval [CI] 23.5-23.7) with kidney stone disease had a prevalent diagnosis of osteoporosis or fracture. In patients with no prior history of osteoporosis or bone mineral density assessment before a kidney stone diagnosis, 9.1% were screened with DXA after their kidney stone diagnosis, of whom 20% were subsequently diagnosed with osteoporosis. Our findings provide support for wider use of bone mineral density screening in patients with kidney stone disease, including middle-aged and older men, a group less well recognized as at risk for osteoporosis or fractures. © 2021 American Society for Bone and Mineral Research (ASBMR).
View details for DOI 10.1002/jbmr.4260
View details for PubMedID 33655611
Analysis of Primary Hyperparathyroidism Screening Among US Veterans With Kidney Stones.
Importance: Approximately 3% to 5% of patients with kidney stones have primary hyperparathyroidism (PHPT), a treatable cause of recurrent stones. However, the rate of screening for PHPT in patients with kidney stones remains unknown.Objectives: To estimate the prevalence of parathyroid hormone (PTH) testing in veterans with kidney stones and hypercalcemia and to identify the demographic, geographic, and clinical characteristics of veterans who were more or less likely to receive PTH testing.Design, Setting, and Participants: This cohort study obtained Veterans Health Administration (VHA) health records from the Corporate Data Warehouse for veterans who received care in 1 of the 130 VHA facilities across the United States from January 1, 2008, through December 31, 2013. Historical encounters, medical codes, and laboratory data were assessed. Included patients had diagnostic or procedural codes for kidney or ureteral stones, and excluded patients were those with a previous serum PTH level measurement. Data were collected from January 1, 2006, to December 31, 2014. Data analysis was conducted from June 1, 2019, to January 31, 2020.Exposures: Elevated serum calcium concentration measurement between 6 months before and 6 months after kidney stone diagnosis.Main Outcomes and Measures: Proportion of patients with a serum PTH level measurement and proportion of patients with biochemical evidence of PHPT who underwent parathyroidectomy.Results: The final cohort comprised 7561 patients with kidney stones and hypercalcemia and a mean (SD) age of 64.3 (12.3) years. Of these patients, 7139 were men (94.4%) and 5673 were white individuals (75.0%). The proportion of patients who completed a serum PTH level measurement was 24.8% (1873 of 7561). Across the 130 VHA facilities included in the study, testing rates ranged from 4% to 57%. The factors associated with PTH testing included the magnitude of calcium concentration elevation (odds ratio [OR], 1.07 per 0.1 mg/dL >10.5 mg/dL; 95% CI, 1.05-1.08) and the number of elevated serum calcium concentration measurements (OR, 1.08 per measurement >10.5 mg/dL; 95% CI, 1.06-1.10) as well as visits to both a nephrologist and a urologist (OR, 6.57; 95% CI, 5.33-8.10) or an endocrinologist (OR, 4.93; 95% CI, 4.11-5.93). Of the 717 patients with biochemical evidence of PHPT, 189 (26.4%) underwent parathyroidectomy within 2 years of a stone diagnosis.Conclusions and Relevance: This cohort study found that only 1 in 4 patients with kidney stones and hypercalcemia were tested for PHPT in VHA facilities and that testing rates varied widely across these facilities. These findings suggest that raising clinician awareness to PHPT screening indications may improve evaluation for parathyroidectomy, increase the rates of detection and treatment of PHPT, and decrease recurrent kidney stone disease.
View details for DOI 10.1001/jamasurg.2020.2423
View details for PubMedID 32725208
Prevalence of twenty-four hour urine testing in Veterans with urinary stone disease.
2019; 14 (8): e0220768
The American Urological Association guidelines recommend 24-hour urine testing in patients with urinary stone disease to decrease the risk of stone recurrence; however, national practice patterns for 24-hour urine testing are not well characterized. Our objective is to determine the prevalence of 24-hour urine testing in patients with urinary stone disease in the Veterans Health Administration and examine patient-specific and facility-level factors associated with 24-hour urine testing. Identifying variations in clinical practice can inform future quality improvement efforts in the management of urinary stone disease in integrated healthcare systems.We accessed national Veterans Health Administration data through the Corporate Data Warehouse (CDW), hosted by the Veterans Affairs Informatics and Computing Infrastructure (VINCI), to identify patients with urinary stone disease. We defined stone formers as Veterans with one inpatient ICD-9 code for kidney or ureteral stones, two or more outpatient ICD-9 codes for kidney or ureteral stones, or one or more CPT codes for kidney or ureteral stone procedures from 2007 through 2013. We defined a 24-hour urine test as a 24-hour collection for calcium, oxalate, citrate or sulfate. We used multivariable regression to assess demographic, geographic, and selected clinical factors associated with 24-hour urine testing.We identified 130,489 Veterans with urinary stone disease; 19,288 (14.8%) underwent 24-hour urine testing. Patients who completed 24-hour urine testing were younger, had fewer comorbidities, and were more likely to be White. Utilization of 24-hour urine testing varied widely by geography and facility, the latter ranging from 1 to 40%.Fewer than one in six patients with urinary stone disease complete 24-hour urine testing in the Veterans Health Administration. In addition, utilization of 24-hour urine testing varies widely by facility identifying a target area for improvement in the care of patients with urinary stone disease. Future efforts to increase utilization of 24-hour urine testing and improve clinician awareness of targeted approaches to stone prevention may be warranted to reduce the morbidity and cost of urinary stone disease.
View details for DOI 10.1371/journal.pone.0220768
View details for PubMedID 31393935
Medical Treatment and Prevention of Urinary Stone Disease.
The Urologic clinics of North America
2022; 49 (2): 335-344
The pathophysiology underlying urinary stone formation remains an area of active investigation. There are many pharmacotherapies aimed at optimizing metabolic factors and reducing urinary supersaturation of stone components that play an important role in urinary stone prevention. In addition, medical expulsive therapy for ureteral stones and medical dissolution therapy for uric acid-based urinary stones are helpful treatment tools and are used alongside surgical treatments in the management of urinary stones.
View details for DOI 10.1016/j.ucl.2021.12.007
View details for PubMedID 35428438
Kidney stone events following parathyroidectomy vs. non-operative management for primary hyperparathyroidism.
The Journal of clinical endocrinology and metabolism
CONTEXT: Primary hyperparathyroidism (PHPT) is associated with an increased risk of kidney stones. Few studies account for PHPT severity or stone risk when comparing stone events after parathyroidectomy vs. non-operative management.OBJECTIVE: Compare the incidence of kidney stone events in PHPT patients treated with parathyroidectomy vs. non-operative management.DESIGN: Longitudinal cohort study with propensity score inverse probability weighting and multivariable Cox proportional hazards regression.SETTING: Veterans Health Administration integrated health care system.PATIENTS: 44,978 patients with >2 years follow-up after PHPT diagnosis (2000-2018). 5,244 patients (11.7%) were treated with parathyroidectomy.MAIN OUTCOMES MEASURE: Clinically significant kidney stone event.RESULTS: The cohort had a mean age of 66.0 years, was 87.8% male, 66.4% White. Patients treated with parathyroidectomy had higher mean serum calcium (11.2 vs. 10.8mg/dL) and were more likely to have a history of kidney stone events. Among patients with baseline history of kidney stones, the unadjusted incidence of ≥1 kidney stone event was 30.5% in patients managed with parathyroidectomy (mean follow-up 5.6 years) compared to 18.0% in those managed non-operatively (mean follow-up 5.0 years). Patients treated with parathyroidectomy had a higher adjusted hazard of recurrent kidney stone events (hazard ratio[HR] 1.98, 95%CI 1.56-2.51); however, this association declined over time (parathyroidectomy*time HR 0.80, 95%CI 0.73-0.87).CONCLUSION: In this predominantly male cohort with PHPT, patients treated with parathyroidectomy continued to be at higher risk of kidney stone events in the immediate years after treatment than patients managed non-operatively, although the adjusted risk of stone events declined with time, suggesting a benefit to surgical treatment.
View details for DOI 10.1210/clinem/dgac193
View details for PubMedID 35363858
Renal Morbidity Following Radical Cystectomy in Patients with Bladder Cancer.
European urology open science
1800; 35: 29-36
Background: Patients with chronic kidney disease (CKD) are poor candidates for standard treatments for muscle-invasive bladder cancer (MIBC) and may be more likely to experience adverse outcomes when diagnosed with MIBC.Objective: To investigate factors associated with the development of advanced CKD following radical cystectomy.Design setting and participants: Using national Veterans Health Administration utilization files, we identified 3360 patients who underwent radical cystectomy for MIBC between 2004 and 2018.Outcome measurements and statistical analysis: We examined factors associated with the development of advanced CKD (estimated glomerular filtration rate [eGFR] of <30 ml/min/1.73 m2) after radical cystectomy using multivariable logistic and proportional hazard regression, with and without consideration of competing risks. We examined survival using Kaplan-Meier product limit estimates and proportional hazard regression.Results and limitations: The median age at surgery was 67 yr and the mean preoperative eGFR was 69.1 ± 20.3 ml/min/1.73 m2. Approximately three out of ten patients (n = 962, 29%) progressed to advanced CKD within 12 mo. Older age (hazard ratio [HR] per 5-yr increase 1.15, 95% confidence interval [CI] 1.10-1.20), preoperative hydronephrosis (HR 1.50, 95% CI 1.29-1.76), adjuvant chemotherapy (HR 1.19, 95% CI 1.00-1.41), higher comorbidity index (HR 1.13, 95% CI 1.11-1.16 per point), and lower baseline kidney function (HR 0.75, 95% CI 0.73-0.78) were associated with the development of advanced CKD. Baseline kidney function at the time of surgery was associated with survival. Generalizability is limited due to the predominantly male cohort.Conclusions: Impaired kidney function at baseline is associated with progression to advanced CKD and mortality after radical cystectomy. Preoperative kidney function should be incorporated into risk stratification algorithms for patients undergoing radical cystectomy.Patient summary: Impaired kidney function at baseline is associated with progression to advanced chronic kidney disease and mortality after radical cystectomy.
View details for DOI 10.1016/j.euros.2021.11.001
View details for PubMedID 35024629
- Twenty-four-hour Urine Testing and Urinary Stone Disease Recurrence in Veterans UROLOGY 2022; 159: 33-40
- Urine oxalate and citrate excretion in patients with kidney stone disease: An ab initio clinical prediction. Physiological reports 2021; 9 (15): e14966
Association of parathyroidectomy with 5-year clinically significant kidney stone events in patients with primary hyperparathyroidism.
Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists
OBJECTIVE: Patients with primary hyperparathyroidism (PHPT) are at increased risk of kidney stones. Guidelines recommend parathyroidectomy in PHPT patients with a history of stone disease. This study aimed to compare the 5-year incidence of clinically significant kidney stone events in patients with PHPT treated with parathyroidectomy vs. non-operative management.METHODS: We performed a longitudinal cohort study of patients with PHPT in a national commercial insurance claims database (2006-2019). Propensity score inverse probability weighting-adjusted multivariable regression models were calculated.RESULTS: We identified 7,623 patients ≥35 years-old with continuous enrollment >1 year before and >5 years after PHPT diagnosis. 2,933 patients (38.5%) were treated with parathyroidectomy. The cohort had a mean age of 66.5 years, 78.1% were female, 72.4% were White. Over 5 years, the unadjusted incidence of ≥1 kidney stone event was higher in patients managed with parathyroidectomy compared to those managed non-operatively overall (5.4% vs. 4.1%) and among those with a history of kidney stones at PHPT diagnosis (17.9% vs. 16.4%). On multivariable analysis, parathyroidectomy was associated with no statistically significant difference in the odds of 5-year kidney stone event among patients with a history of kidney stones (OR 1.03, 95%CI 0.71-1.50) or those without history of kidney stones (OR 1.16, 95%CI 0.84-1.60).CONCLUSION: Based on this claims analysis, there was no difference in the odds of 5-year kidney stone events in PHPT patients treated with parathyroidectomy vs. non-operative management. Time-horizon for benefit should be considered when making treatment decisions for PHPT based on risk of kidney stone events.
View details for DOI 10.1016/j.eprac.2021.06.004
View details for PubMedID 34126246
Removing Race from eGFR calculations: Implications for Urologic Care.
Equations estimating the glomerular filtration rate are important clinical tools in detecting and managing kidney disease. Urologists extensively use these equations in clinical decision making. For example, the estimated glomerular function rate is used when considering the type of urinary diversion following cystectomy, selecting systemic chemotherapy in managing urologic cancers, and deciding the type of cross-sectional imaging in diagnosing or staging urologic conditions. However, these equations, while widely accepted, are imprecise and adjust for race which is a social, not a biologic construct. The recent killings of unarmed Black Americans in the US have amplified the discussion of racism in healthcare and has prompted institutions to reconsider the role of race in eGFR equations and raced-based medicine. Urologist should be aware of the consequences of removing race from these equations, potential alternatives, and how these changes may affect Black patients receiving urologic care.
View details for DOI 10.1016/j.urology.2021.03.018
View details for PubMedID 33798557
The Urine Albumin-Creatinine Ratio and Kidney Function after Nephrectomy.
The Journal of urology
BACKGROUND: Patients with kidney cancer are at risk of developing chronic kidney disease (CKD) after radical and partial nephrectomy. We sought to determine if the urine albumin-creatinine ratio (UACR) is independently associated with progressive CKD after nephrectomy.METHODS: We performed a cohort study based within a large, integrated health care system. We identified patients who underwent radical or partial nephrectomy from 2004 to 2014 with UACR measured in the 12 months prior to surgery. We fit multivariable models to determine if the UACR was associated with the time to CKD progression (defined as reaching stage 4 or 5 CKD, eGFR <30 mL/min/1.73m2). We performed a parallel analysis measuring the time to stage 3b, 4 or 5 CKD (eGFR <45 mL/min/1.73m2) among patients with normal or near-normal preoperative kidney function (eGFR ≥60 mL/min/1.73 m2). We also examined the association between UACR and survival.RESULTS: 1930 patients underwent radical or partial nephrectomy and had preoperative UACR and pre- and post-operative eGFR. Of these, 658 (34%) and 157 (8%) had moderate (UACR 30-300mg/g) or severe albuminuria (UACR > 300mg/g), respectively. Albuminuria severity was independently associated with progressive CKD after radical (moderate albuminuria HR 1.7, 95%CI 1.4-2.2; severe albuminuria HR 2.3, 95%CI 1.7-3.1) and partial nephrectomy (moderate albuminuria HR 1.8, 95%CI 1.2-2.7; severe albuminuria HR 4.3, 95%CI 2.7-7.0). Albuminuria was also associated with survival following radical and partial nephrectomy.CONCLUSIONS: In patients undergoing radical or partial nephrectomy, the severity of albuminuria can stratify risk of progressive CKD.
View details for DOI 10.1097/JU.0000000000001005
View details for PubMedID 32125227
Urinary Stone Disease in Pregnancy: A Claims-Based Analysis of 1.4 Million Patients.
The Journal of urology
PURPOSE: Urinary stone disease during pregnancy is poorly understood but is thought to be associated with increased maternal and fetal morbidity. We sought to determine the prevalence of urinary stone disease in pregnancy and whether urinary stone disease during pregnancy is associated with adverse pregnancy outcomes.MATERIALS AND METHODS: We identified all pregnant women from 2003 through 2017 in the Optum national insurance claims database. We used diagnosis claims to identify urinary stone disease and assess medical comorbidity. We established the prevalence of urinary stone disease during pregnancy, stratified by week of pregnancy. We further evaluated associations among urinary stone disease and maternal complications and pregnancy outcomes in both univariable and multivariable analyses.RESULTS: Urinary stone disease affects 8/1000 pregnancies and is more common in white women and women with more comorbid conditions. In fully adjusted models, pregnancies complicated by urinary stone disease had higher rates of adverse fetal outcomes, including prematurity and spontaneous abortions. This analysis is limited by its retrospective administrative claims design.CONCLUSIONS: The rate of urinary stone disease during pregnancy is higher than previously reported. Urinary stone disease is associated with adverse pregnancy outcomes.
View details for DOI 10.1097/JU.0000000000000657
View details for PubMedID 31738114
Ultra-low-dose CT: An Effective Follow-up Imaging Modality for Ureterolithiasis.
Journal of endourology
BACKGROUND AND PURPOSE: Classically, abdominal X-ray (KUB), ultrasound or a combination of both have been routinely used for ureteral stone surveillance after initial diagnosis. More recently, ultra-low-dose CT (ULD CT) has emerged as a CT technique that reduces radiation dose while maintaining high sensitivity and specificity for urinary stone detection. We aim to evaluate our initial experience with ULD CT for patients with ureterolithiasis, measuring real-world radiation doses and stone detection performance.METHODS: We reviewed all ULD CT scans performed at the Veterans Affairs Palo Alto Health Care System between 2016 and 2018. We included patients with ureteral stones and calculated the mean effective radiation dose per scan. We determined stone location and size, if the stone was visible on the associated KUB or CT scout film, and if hydronephrosis was present. We performed logistic regression to identify variables associated with visibility on KUB or CT scout film and hydronephrosis.RESULTS: One-hundred and eighteen ULD scans were reviewed, of which 50 detected ureteral stones. The mean effective radiation dose was 1.04 ± 0.41 mSv. Of the ULD CTs that detected ureterolithiasis, 38% lacked visibility on KUB/CT scout film and had no associated hydronephrosis, suggesting they would be missed with a combination of KUB and ultrasound. Larger stones (OR: 1.40, 95% CI: 1.08-1.96 for every 1mm increase in stone size) were more likely to be detected by KUB/CT scout or ultrasound, while stones in the distal ureter (OR: 0.18, 95% CI: 0.03-0.81) were more likely to be missed by KUB/CT scout or hydronephrosis.CONCLUSION: Based on our institutions' initial experience with ULD CT, ULD CT detects small and distal ureteral stones that would likely be missed by KUB or ultrasound, while maintaining a low effective radiation dose. An ULD CT protocol should be considered when re-imaging for ureteral stones is necessary.
View details for DOI 10.1089/end.2019.0574
View details for PubMedID 31663371
Spironolactone plus patiromer: proceed with caution
2019; 394 (10208): 1486–88
View details for Web of Science ID 000493399500007
Twenty-Four Hour Urine Testing and Prescriptions for Urinary Stone Disease-Related Medications in Veterans.
Clinical journal of the American Society of Nephrology : CJASN
Current guidelines recommend 24-hour urine testing in the evaluation and treatment of persons with high-risk urinary stone disease. However, how much clinicians use information from 24-hour urine testing to guide secondary prevention strategies is unknown. We sought to determine the degree to which clinicians initiate or continue stone disease-related medications in response to 24-hour urine testing.We examined a national cohort of 130,489 patients with incident urinary stone disease in the Veterans Health Administration between 2007 and 2013 to determine whether prescription patterns for thiazide diuretics, alkali therapy, and allopurinol changed in response to 24-hour urine testing.Stone formers who completed 24-hour urine testing (n=17,303; 13%) were significantly more likely to be prescribed thiazide diuretics, alkali therapy, and allopurinol compared with those who did not complete a 24-hour urine test (n=113,186; 87%). Prescription of thiazide diuretics increased in patients with hypercalciuria (9% absolute increase if urine calcium 201-400 mg/d; 21% absolute increase if urine calcium >400 mg/d, P<0.001). Prescription of alkali therapy increased in patients with hypocitraturia (24% absolute increase if urine citrate 201-400 mg/d; 34% absolute increase if urine citrate ≤200 mg/d, P<0.001). Prescription of allopurinol increased in patients with hyperuricosuria (18% absolute increase if urine uric acid >800 mg/d, P<0.001). Patients who had visited both a urologist and a nephrologist within 6 months of 24-hour urine testing were more likely to have been prescribed stone-related medications than patients who visited one, the other, or neither.Clinicians adjust their treatment regimens in response to 24-hour urine testing by increasing the prescription of medications thought to reduce risk for urinary stone disease. Most patients who might benefit from targeted medications remain untreated.
View details for DOI 10.2215/CJN.03580319
View details for PubMedID 31712387
Regarding the possibility of anterior vascular injury from the posterior approach to the lumbar disc space: an anatomical study.
2012; 37 (22): E1371-5
Anatomical study with magnetic resonance imaging data.To document the distances between the major retroperitoneal vessels and the anterior lumbar disc spaces; to determine the effect of patient positioning on these relationships; and to discuss ways to deal with vascular injury.It is well known that there are major vascular structures anterior to the lower lumbar spine. Vascular injury during posterior approaches, however, remains a problem. These anatomical relationships have not been determined in vivo, and there are no data on the effect of turning the patient prone, and onto bolsters.A random sampling of 49 women and 48 men was made. All examinations were performed in magnetic resonance scanners operating at 1.5 T. Measurements were made using electronic calipers on axial T2-weighted images. Post hoc studies were done on a smaller number of patients, to determine the effect of prone positioning.At the L4-L5 level, 66% of the common iliac arteries in women and 49% of those in men were within 5 mm of the anterior aspect of the disc space. At L5-S1, these numbers dropped to 23% for women and 19% for men. No relationship between the age of the patient and the distance from disc space to blood vessel was found. There was little change in these measurements between the supine and prone positions. The use of bolsters to decompress the abdominal contents in the prone position did not significantly alter the disc-artery distances. Venous relationships were also documented.The lower lumbar spine is confirmed to frequently be very close to the major retroperitoneal vessels. Turning the patient prone and placing the patient on bolsters does not change this relationship. This is part of the reason why vascular injuries may occur during routine lumbar spine surgery. Spine surgeons should be able to recognize and initiate treatment of such injuries.
View details for DOI 10.1097/BRS.0b013e318267fb36
View details for PubMedID 22781009