{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,11]],"date-time":"2026-08-11T21:31:26Z","timestamp":1786483886732,"version":"build-2736575974"},"reference-count":20,"publisher":"Ovid Technologies (Wolters Kluwer Health)","issue":"5","funder":[{"name":"US Department of VA Clinical Sciences Research and Development Service Merit Award I01","award":["CX001695"],"award-info":[{"award-number":["CX001695"]}]}],"content-domain":{"domain":["lww.com","ovid.com"],"crossmark-restriction":true},"short-container-title":["Kidney360"],"published-print":{"date-parts":[[2022,5,26]]},"abstract":"<jats:sec>\n                    <jats:title>Key Points<\/jats:title>\n                    <jats:p>\n                      <jats:list list-type=\"bullet\">\n                        <jats:list-item>\n                          <jats:p>Plasma ammonium assay reliably quantifies urine ammonium at physiologic concentrations.<\/jats:p>\n                        <\/jats:list-item>\n                        <jats:list-item>\n                          <jats:p>The enzymatic method compares well with the formalin titration method and is suitable for routine clinical use.<\/jats:p>\n                        <\/jats:list-item>\n                      <\/jats:list>\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>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 United States, 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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>An enzymatic plasma ammonium assay (Randox) was modified to measure urinary ammonium concentration. Urine samples were diluted 40-fold and 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.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>After dilution, the assay had total precision of 18% at 2.54 mmol\/L, 5% at 15.58 mmol\/L, and 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\u201345 mmol\/L. Method comparison against the formalin method showed a slope of 0.98 and intercept of \u20130.37 mmol\/L. Urinary ammonium was determined to be stable for 48 hours at room temperature and for 9 days at 4\u00b0C and \u201320\u00b0C at pH 5.6\u20136.3. Ammonium was less stable at pH 3.8 and 8.5. When stored at \u201380\u00b0C, urinary ammonium was stable for at least 24 months.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>The modified enzymatic plasma ammonium assay reliably quantifies urine ammonium at physiologic concentrations. It compares well with the formalin titration method and is suitable for routine clinical use on an automated chemistry analyzer.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.34067\/kid.0000262022","type":"journal-article","created":{"date-parts":[[2022,2,11]],"date-time":"2022-02-11T10:10:15Z","timestamp":1644574215000},"page":"926-932","update-policy":"https:\/\/doi.org\/10.1097\/lww.0000000000001000","source":"Crossref","is-referenced-by-count":13,"title":["Measurement of Urinary Ammonium Using a Commercially Available Plasma Ammonium Assay"],"prefix":"10.34067","volume":"3","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3054-7803","authenticated-orcid":false,"given":"Valentinas","family":"Gruzdys","sequence":"first","affiliation":[{"name":"Doctor\u2019s Data, St. Charles, Illinois"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kenneth","family":"Cahoon","sequence":"additional","affiliation":[{"name":"ARUP Laboratories, Salt Lake City, Utah"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lauren","family":"Pearson","sequence":"additional","affiliation":[{"name":"Department of Pathology, University of Utah School of Medicine, Health Sciences Center, Salt Lake City, Utah"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1378-2609","authenticated-orcid":false,"given":"Kalani L.","family":"Raphael","sequence":"additional","affiliation":[{"name":"Division of Nephrology and Hypertension, Department of Medicine, Oregon Health and Science University and VA Portland Health Care System, Portland, Oregon"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"276","published-online":{"date-parts":[[2022,5,26]]},"reference":[{"key":"B1-20250825","doi-asserted-by":"crossref","first-page":"670","DOI":"10.1053\/j.ajkd.2013.01.017","article-title":"Association of serum bicarbonate with risk of renal and cardiovascular outcomes in CKD: A report from the Chronic 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