Response to “Association Between Dietary Potassium Intake and Serum Potassium in CKD”

We appreciate the commentary provided by Dr. Brown highlighting an important consideration related to potassium tolerance. Accordingly, in this letter, we discuss the topic of potassium tolerance which was not covered in our paper, as Dr. Brown mentioned.1Ogata S. Akashi Y. Kato S. et al.Association between dietary potassium intake estimated from multiple 24-hour urine collections and serum potassium in patients with CKD.Kidney Int Rep. 2023; 8: 584-595https://doi.org/10.1016/j.ekir.2022.12.005Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar The reason for this was that it is not currently standard practice to avoid fasting when measuring serum potassium levels in clinical settings.2MedlinePlus. Potassium blood test.https://medlineplus.gov/lab-tests/potassium-blood-test/Date accessed: April 16, 2023Google Scholar In addition, many of the reports supporting potassium tolerance were based on animal experiments.3Thatcher J.S. Radike A.W. Tolerance to potassium intoxication in the albino rat.Am J Physiol. 1947; 151: 138-146https://doi.org/10.1152/AJPLEGACY.1947.151.1.138Crossref PubMed Google Scholar,4Silva P. Brown R.S. Epstein F.H. Adaptation to potassium.Kidney Int. 1977; 11: 466-475https://doi.org/10.1038/KI.1977.64Abstract Full Text PDF PubMed Google Scholar It is unclear whether the same effects occur in patients with chronic kidney disease (CKD) whose ability to tolerate potassium may be impaired.S1 In fact, potassium tolerance was seen to be impaired in patients receiving dialysis.S2 We agree with Dr Brown's comment on the importance of monitoring nonfasting serum potassium levels in patients with CKD when increasing dietary potassium because of the following, even though it is not currently standard practice to avoid fasting when measuring serum potassium levels. If potassium tolerance is found to be impaired in patients with CKD, an increased intake of dietary potassium would acutely elevate plasma or serum potassium levels, similar to what has been observed in patients receiving dialysis.6 Conversely, if potassium tolerance is found to occur in patients with CKD, it would result in a paradoxical situation where measuring serum potassium levels in patients with CKD who have fasted overnight may lead to lower serum potassium levels in those on high potassium diets than in those on low potassium diets.3Thatcher J.S. Radike A.W. Tolerance to potassium intoxication in the albino rat.Am J Physiol. 1947; 151: 138-146https://doi.org/10.1152/AJPLEGACY.1947.151.1.138Crossref PubMed Google Scholar,4Silva P. Brown R.S. Epstein F.H. Adaptation to potassium.Kidney Int. 1977; 11: 466-475https://doi.org/10.1038/KI.1977.64Abstract Full Text PDF PubMed Google Scholar In our paper,1Ogata S. Akashi Y. Kato S. et al.Association between dietary potassium intake estimated from multiple 24-hour urine collections and serum potassium in patients with CKD.Kidney Int Rep. 2023; 8: 584-595https://doi.org/10.1016/j.ekir.2022.12.005Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar we took blood samples from our study patients while they were fasting. If these patients with CKD had potassium tolerance, it is possible that the serum potassium levels used in our analysis were lower than the levels after they ate foods as a source of dietary potassium during the day. As Dr. Brown pointed out, when managing serum potassium levels in patients with CKD, it is important to pay attention to the possibility that their levels after eating may be higher than their fasting levels. We greatly appreciate Dr. Brown's valuable input. Download .pdf (.01 MB) Help with pdf files Supplementary File (PDF) Supplementary References. Association Between Dietary Potassium Intake and Serum Potassium in CKDKidney International ReportsVol. 8Issue 7PreviewIn the March 2023 issue of Kidney International Reports, a well-done study by Ogata et al.1 found significant, but only weak, associations between the dietary potassium intake and the serum potassium in patients with CKD. In an accompanying Commentary, Joshi et al.2 state that "their study adds to a growing body of evidence that suggests a weak association of dietary potassium with serum potassium" and "between dietary potassium and hyperkalemia." But surprisingly, neither article cites a crucial limitation that the serum potassium levels in this study were measured "fasting" after collection of the 24-hour urine, so presumably after fasting overnight. Full-Text PDF Open Access