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AUA 2019

AUA 2019: Higher Salt Intake and Non-Dipping Blood Pressure are Associated with Nocturnal Polyuria in Patients with Lower Urinary Tract Symptoms

Chicago, Illinois (UroToday.com) This podium session contained a broad scope of topics in the management of men with lower urinary tract symptoms (LUTS). The specific symptom of nocturia is one of the most significant contributors to overall agitation and has also been one of the most difficult LUTS symptoms to treat. Nocturia is often correlated with nocturnal polyuria, which has multi-potential mechanisms of cause. One such recent proposed mechanism is that of non-dipping blood pressure overnight.1 With this recent correlation between elevated blood pressure and nocturia and/or nocturnal polyuria, additional inquiries are being made in terms of affirming this correlation and ways to potentially utilize this knowledge to treat nocturia. Building upon this, the authors looked closer at patients with resistant hypertension (uncontrolled blood pressure on three or more anti-hypertensive medications) and salt intake to further develop a better understanding of this mechanism.

This was a prospective study of 323 patients (256 male, 67 female) with history of LUTS at median age of 72 (65-92). Data was collected in regards to their medication use and medical history, and they were each evaluated with a 24 hour voiding diary (volume and frequency) in order to establish a nocturnal polyuria index (NPi) for each, using a cutoff of 0.33 to define nocturnal polyuria. Patients were then divided into two groups, those with and without nocturnal polyuria (NP). Thirty-four patients (17 NP and 17 without NP) were then selected and monitored using a portable automatic blood pressure monitor. Appropriately dipping blood pressure (BP) was defined as a >10% drop in BP overnight, and non-dipping as <10% or any increase. For estimating daily salt intake they used spot urine samples and checked urine sodium and creatine as well as Tanaka’s formula.2 After the first analysis of the 323 patients, they discovered that 175 patients were in the NP group, and 148 patients were in the non-NP group. Patients who took 3 or more antihypertensives or diuretics were found at a significantly higher rate via chi-square analysis in the NP group as compared to the non-NP group (10.3% vs. 4.1%, p=0.034). Non-dipping blood pressure was observed at a significantly higher rate via chi-square analysis in the NP group as compared to the non-NP group (76.5% vs. 41.2%, p=0.0369). 

AUA 2019 Frequency of BP Pattern   

The average daily salt intake was also found to be significantly higher by Wilcoxon rank sum test in the NP group as compared to the non-NP group (9.73 vs. 7.69g/day, p=0.485).
AUA 2019 Estimated Daily Salt Intake
The authors then conclude that there are correlations not only with resistant hypertension and nocturnal polyuria (which seemed to be the most significant), but also a correlation with both non-dipping blood pressure and daily salt intake with nocturnal polyuria. The challenges with this study are in the difficulties reliably measuring overnight blood pressure and obtaining adequate enrollment and data. However, this is building upon a now growing body of knowledge in regards to nocturnal polyuria, either as a warning sign of poorly controlled blood pressure or as a result of non-dipping blood pressure. The next steps will be to determine if we can further manage nocturia and/or nocturnal polyuria via improved blood pressure management or diet (lower salt intake).    

Presented by: Misato Takayama, MD, Department of Urology, Iwate Medical University 

Written by: Ross Moskowitz, MD, Assistant Clinical Professor of Urology, University of California Irvine Medical Center, Twitter: @rossmosk1 at the American Urological Association's 2019 Annual Meeting (AUA 2019), May 3 – 6, 2019 in Chicago, Illinois 

References:
1. Takayama M, Omori S, Iwasaki K, Shiomi E, Takata R, Sugimura J, Abe T, Obara W. "Relationship between nocturnal polyuria and non-dipping blood pressure in male patients with lower urinary tract symptoms."Low Urin Tract Symptoms. 2019 Apr;11(2):O98-O102. doi: 10.1111/luts.12225. Epub 2018 May 29.
2. Tanaka T, Okamura T, Miura K, Kadowaki T, Ueshima H, Nakagawa H, Hashimoto T. A simple method to estimate populational 24-h urinary sodium and potassium excretion using a casual urine specimen. J Hum Hypertens. 2002 Feb;16(2):97-103.
CrPr24h (mg) = [(14.89 x weight, kg) + (16.14 x height, cm) (2.04 x age, years)] - 2,244,45
NaUr (mEq) = [Na casual urine, mEq/L/(Cr casual urine, mg/dL x 10)] x CrPr24 h (mg)