Nephrolithiasis and Elevated Urinary Ammonium: A Matched Comparative Study

Sui, Wilson; Hancock, Joel; Asplin, John R.; Gould, Edward R.; Hsi, Ryan S.

doi:10.1016/j.urology.2020.05.063

Cited by 8 publications

(8 citation statements)

References 22 publications

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“…To account for dietary acid ash content, we examined the difference of urinary ammonium to urinary sulfate (NH 4 -SO 4 ). 23 A two-sided P-value of <0.05 was considered statistically significant. All analyses were performed using SPSS v25.…”

Section: Discussionmentioning

confidence: 99%

Association of Chronic Kidney Disease Stage with 24-Hour Urine Values Among Patients with Nephrolithiasis

Sui

Calvert

Kavoussi

et al. 2020

Journal of Endourology

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Introduction: Nephrolithiasis is a known risk factor for chronic kidney disease (CKD); however, it is unknown how CKD affects urinary parameters related to stone risk. The purpose of this study was to assess the relationship of diminishing glomerular filtration rate (GFR) and kidney stone-related 24-hour urine (24H urine) composition. Materials and Methods: A single-institution retrospective review of patients (n = 2057) who underwent 24H urine analysis was performed. The serum creatinine within 1 year of the first 24H urine was used to determine estimated GFR and stratify patients by CKD stage. We performed analysis of variance and multivariable linear regression to assess the relationship of GFR and urinary analytes. Results: Among all patients, there were 184 (8.9%), 1537 (74.7%), 245 (11.9%), 70 (3.4%), 17 (0.8%), and 4 (0.2%) in CKD stage I, II, IIIa, IIIb, IV, and V groups, respectively. On analysis of 24H urine composition, as CKD increased, changes in urinary parameters protective against crystallization included decreased calcium and uric acid (UA) (P < 0.001). In addition, parameters favoring crystallization included decreased citrate and magnesium (P = 0.002 and P < 0.001, respectively). The net effect with increasing GFR was decreasing supersaturation of calcium oxalate and phosphate. On linear regression, urinary excretion of calcium, oxalate, citrate, UA, phosphate, and ammonia all decreased with decreasing GFR (all P < 0.05). Conclusions: Higher CKD stage was associated with changes in urinary analytes that both promoted and inhibited stone formation, with the net effect of decreasing calcium oxalate and phosphate supersaturation. These patients may benefit from medical therapy that targets improving urinary citrate instead of lowering calcium or UA.

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Section: Discussionmentioning

confidence: 99%

Association of Chronic Kidney Disease Stage with 24-Hour Urine Values Among Patients with Nephrolithiasis

Sui

Calvert

Kavoussi

et al. 2020

Journal of Endourology

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“…In patients with nephrolithiasis, high urinary ammonium levels could signal the presence of urease producing bacteria and struvite stones or a high protein diet. 10 In summary, the enzymatic plasma ammonium assay used here reliably quantified urinary ammonium concentration after specimen dilution. The modified assay we used had broad analytical measurement range (2.92 -45.0 mmol/L in undiluted urine), which is expected to quantify ammonium in most patient samples without additional dilution.…”

Section: Discussionmentioning

confidence: 86%

“…Quantification of urinary ammonium levels is also helpful in evaluating patients with normal anion gap metabolic acidosis to determine if the etiology is due to diarrhea or renal tubular acidosis (RTA) (8,9). Urinary ammonium levels can also aid in the management of patients with nephrolithiasis by providing an assessment of the daily acid load, provided kidney function is normal and there is no co-existing RTA, or signaling the presence of struvite stones (10).…”

Section: Introductionmentioning

confidence: 99%

“…8,9 Urinary ammonium levels can also aid in the management of patients with nephrolithiasis by providing an assessment of the daily acid load, provided kidney function is normal and there is no co-existing RTA, or signaling the presence of struvite stones. 10 Unfortunately, few clinical laboratories offer urinary ammonium testing. Therefore, clinicians use surrogates such as the urinary anion gap and urinary osmolal gap to estimate urinary ammonium concentration.…”

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confidence: 99%

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Measurement of Urinary Ammonium Using a Commercially Available Plasma Ammonium Assay

Gruzdys¹,

Cahoon²,

Pearson³

et al. 2022

Kidney360

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Background: Determination of urinary ammonium excretion is helpful in evaluating patients with acid-base disorders, chronic kidney disease, and nephrolithiasis. However, urinary ammonium levels are only measured by specialized laboratories in the US limiting widespread implementation. We evaluated the performance of a plasma ammonium assay to quantify urinary ammonium excretion and also determined ammonium stability under a variety of conditions. Methods: An enzymatic plasma ammonium assay (Randox®, Ireland) was modified to measure urinary ammonium concentration. Urine samples were diluted 40-fold then assayed on an Abbott Architect ci8200 analyzer. Assay precision, limit of quantitation, and linearity were determined. The method was compared against the formalin titration method and stability studies were conducted at different temperatures and pH. Results: After dilution, the assay had total precision of 17.7% at 2.54 mmol/L, 5.1% at 15.58 mmol/L, and 2.2% at 29.49 mmol/L with a limit of quantitation of 2.92 mmol/L. Assay performance was linear in the range of 0.7-45.0 mmol/L. Method comparison against the formalin method showed a slope of 0.98 and intercept of -0.37 mmol/L. Urinary ammonium was determined to be stable for 48h at room temperature and for 9 days at 4oC and -20oC at pH 5.6-6.3. Ammonium was less stable at pH 3.8 and 8.5. When stored at -80oC, urinary ammonium was stable for at least 24 months. Conclusion: The modified enzymatic plasma ammonium assay reliably quantifies urine ammonium at physiological concentrations. It compares well with formalin-titration method and is suitable for routine clinical use on an automated chemistry analyzer.

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“…If the gastrointestinal alkali loss is also associated with potassium depletion and volume depletion with low sodium delivery to the distal nephron, urine pH can rise to 6 or slightly higher, represented by the slanted dashed line in the lower right quadrant of the graph. This situation can be confused with dRTA, but the high NH 4 – SO 4 value clearly rules out dRTA [33,34 ▪ ].…”

Section: Clinical Applicationmentioning

confidence: 99%

Neglected analytes in the 24-h urine: ammonium and sulfate

Asplin¹

2021

Current Opinion in Nephrology &Amp; Hypertension

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Purpose of reviewEvaluation of the kidney stone patient includes measurement of 24 h urine chemistries. This review summarizes the application of physiologic principles to the interpretation of urine chemistries, using sulfate and ammonium to estimate diet acid load, and the renal response. Recent findingsThere has been increased recognition of the need to measure urine ammonium excretion in the clinical setting in order to understand renal acid excretion. Some 24 h urine kidney stone panels include ammonium measurements, providing an opportunity to apply this measurement to clinical practice. In order to better interpret ammonium excretion, one needs an estimate of dietary acid load to understand the driving forces for ammonium excretion. Sulfate is also included in some kidney stone panels and functions as an estimate of diet acid load. Combining these analytes with urine pH, the clinician can quickly estimate dietary stone risk as well as potential bowel disease, acidification disorders, and the presence of urease producing bacteria; all of which can affect stone risk.

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Nephrolithiasis and Elevated Urinary Ammonium: A Matched Comparative Study

Cited by 8 publications

References 22 publications

Association of Chronic Kidney Disease Stage with 24-Hour Urine Values Among Patients with Nephrolithiasis

Association of Chronic Kidney Disease Stage with 24-Hour Urine Values Among Patients with Nephrolithiasis

Measurement of Urinary Ammonium Using a Commercially Available Plasma Ammonium Assay

Neglected analytes in the 24-h urine: ammonium and sulfate

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