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Residual Urine Volume and Quality of Life in Maintenance Hemodialysis

This cross-sectional study of 99 hemodialysis patients reveals that higher residual urine volume is independently associated with better quality of life, suggesting that strategies to preserve residual urine may improve patient-centered outcomes.

Original authors: Hyun Lee Ko, Soojin Lee, Dha Woon Im, Sung Woo Lee

Published 2026-07-27

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Hyun Lee Ko, Soojin Lee, Dha Woon Im, Sung Woo Lee

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body as a bustling city with a massive water treatment plant. In a healthy city, this plant works overtime, filtering out waste and excess water every single day, sending it out through the pipes so the streets stay clean and dry. But for some people, the city's main water plant (the kidneys) has shut down. To keep the city from flooding, a giant, external truck (a dialysis machine) has to come in three times a week to suck out all the extra water and toxins.

This is the reality for people on hemodialysis. Because the external truck has to do all the heavy lifting, doctors often have to tell patients to drink almost no water and eat very little salt. It's like living in a city where you're only allowed to sip a tiny cup of water a day, no matter how thirsty you are. This strict rule is necessary to keep the water levels safe between truck visits, but it can be exhausting, stressful, and make daily life feel very small and restricted.

Now, here is the twist: sometimes, even when the main water plant is broken, a few tiny, hidden pipes (the remaining kidney function) might still be working just enough to let a little bit of water flow out on its own. Scientists have long known that having even a little bit of this "leftover" water flow is good for physical survival. But a new question has been bubbling up: Does having a little bit of this natural flow also make people feel better? Does it change their happiness, their mood, and their ability to enjoy life, or is it just a number on a medical chart?

The Story of the "Leftover" Water

A team of researchers from Uijeongbu Eulji University Medical Center in Korea decided to play detective with this question. They looked at 99 people who were currently riding the dialysis train. Their mission was to see if the amount of urine these patients could still produce on their own (called "residual urine volume") was connected to how happy and satisfied they felt with their lives (their "Quality of Life").

To get the facts, the researchers asked the patients to collect all their urine for a full 24 hours on a day when they didn't go to the dialysis center. They weighed the urine to get an exact number. Then, they split the patients into three groups based on how much "leftover" water they had:

The Dry Group: 0 mL/day (No natural flow at all).
The Drip Group: 1–520 mL/day (A small trickle).
The Flow Group: More than 520 mL/day (A steady stream).

They then asked everyone to fill out a special questionnaire called the EQ-5D-5L. Think of this as a report card for life, where students rate themselves on things like moving around, taking care of themselves, doing normal activities, feeling pain, and feeling anxious or depressed. The researchers gave everyone a score, and they decided that a score of 0.82 or higher meant "Good Quality of Life," while anything lower meant "Poor Quality of Life."

What They Found

The results were like watching a lightbulb get brighter as you turn up the dial. The researchers found a clear pattern: the more urine the patients could produce on their own, the more likely they were to have a "Good Quality of Life."

In the Dry Group (0 mL), only about 41% of patients felt they had a good quality of life.
In the Drip Group (1–520 mL), that number went up to 50%.
But in the Flow Group (more than 520 mL), a whopping 70% of patients reported having a good quality of life.

When the researchers did the math to make sure this wasn't just a coincidence caused by other factors (like age, how long they had been on dialysis, or other health problems), the connection held strong. They found that patients in the Flow Group were about 5.4 times more likely to have a good quality of life compared to those in the Dry Group.

The researchers also used a special mathematical tool (called a "restricted cubic spline") to see if the relationship was a straight line or a bumpy curve. They found it was mostly a straight, upward climb: as the urine volume went up, the chances of a happy life went up too. There wasn't a weird "sweet spot" where having too much urine suddenly became bad; it just kept getting better.

Why This Matters (And What It Doesn't Say)

The paper suggests that keeping those tiny pipes open and flowing is a big deal. It's not just about saving lives or balancing salt; it seems to be about saving the spirit of the patient. When patients can still pee a little bit on their own, they might not have to be as strict with their water restrictions, they might feel less swollen between treatments, and they might have more energy to do the things they love.

However, the authors are careful to tell us that this is a snapshot in time. They took a picture of everyone on one day and looked at the connections. Because of this, they cannot say for sure that the urine caused the happiness. It's possible that people who are happier and more active also happen to have better kidney function, or that some other hidden factor is helping both. They also note that their group of 99 people was relatively small, so while the results are exciting, they need to be confirmed with bigger studies in the future.

In short, this study paints a hopeful picture: holding onto even a little bit of natural kidney function might be the key to unlocking a happier, more flexible life for people on dialysis. It suggests that doctors and patients should fight hard to protect those last few drops of natural flow, not just for the body, but for the soul.

Technical Summary: Residual Urine Volume and Quality of Life in Maintenance Hemodialysis

Problem Statement
In patients undergoing maintenance hemodialysis, residual urine volume is a well-established physiological indicator linked to fluid balance, interdialytic weight gain, ultrafiltration requirements, and mortality risk. While the physiological consequences of declining residual urine volume are documented, its specific association with Quality of Life (QOL)—a critical patient-centered outcome—remains insufficiently characterized. Existing literature has largely focused on patients with very low or anuric states or has relied on coarse, dichotomous definitions of residual function. Consequently, there is a lack of quantitative evidence describing how variations across a broad spectrum of residual urine volume relate to patient-reported outcomes in routine clinical practice.

Methodology
This study employed a cross-sectional design involving 99 patients undergoing hemodialysis at a single center in Korea (Uijeongbu Eulji University Medical Center). Data were collected over a one-year period in 2024.

Exposure Variable: Residual urine volume was measured via 24-hour urine collection on a non-dialysis day to minimize the confounding effects of dialysis-related fluid removal. Participants were stratified into three groups based on volume: 0 mL/day ( $n=39$ ), 1–520 mL/day ( $n=30$ ), and >520 mL/day ( $n=30$ ), with 520 mL representing the median of non-zero volumes.
Outcome Variable: QOL was assessed using the EuroQol 5-dimension 5-level questionnaire (EQ-5D-5L). The resulting index scores were dichotomized at the study median (0.82) to define "good" (≥0.82) versus "poor" (<0.82) QOL.
Statistical Analysis: The authors utilized logistic regression with Firth's penalized likelihood method to address potential small-sample bias and data sparsity. Analyses included univariate and multivariable models (Model 1 adjusted for demographics; Model 2 further adjusted for comorbidities, dialysis parameters, and laboratory variables). To assess dose-response relationships and potential nonlinearity, restricted cubic spline models with four knots were applied.

Key Results
The study identified a positive, graded association between residual urine volume and the likelihood of reporting good QOL.

Descriptive Trends: The proportion of patients with good QOL increased across the urine volume categories: 41.0% in the 0 mL/day group, 50.0% in the 1–520 mL/day group, and 70.0% in the >520 mL/day group.
Multivariable Analysis: After adjusting for age, sex, comorbidities (hypertension, diabetes), dialysis vintage, ultrafiltration rate, and laboratory markers, residual urine volume >520 mL/day was independently associated with significantly higher odds of good QOL compared to the anuric group (0 mL/day). The adjusted odds ratio (aOR) was 5.40 (95% CI: 1.23–27.09; $P=0.025$ ). The intermediate group (1–520 mL/day) did not show a statistically significant association with good QOL relative to the anuric group in the adjusted model.
Dose-Response: Restricted cubic spline analysis indicated a generally increasing trend in the likelihood of good QOL with higher residual urine volume. The analysis did not detect significant nonlinearity, suggesting a consistent association across the observed range.
Clinical Correlates: Patients with higher residual urine volumes had significantly shorter dialysis vintage, lower ultrafiltration rates, and higher prescribed oral furosemide doses compared to those with no residual urine.

Key Contributions

Quantitative Granularity: Unlike previous studies that often dichotomized residual function or focused exclusively on anuric populations, this study evaluated residual urine volume across a broad quantitative spectrum, enabling the assessment of graded associations with QOL.
Patient-Centered Focus: The research explicitly links a physiological metric (residual urine volume) to a validated patient-reported outcome (EQ-5D-5L), reinforcing the importance of residual renal function beyond survival and fluid management.
Robust Statistical Handling: The application of Firth's penalized likelihood and restricted cubic splines allowed for rigorous analysis despite the modest sample size and potential nonlinearity.

Significance and Claims
The authors conclude that higher residual urine volume is independently associated with better QOL in hemodialysis patients. They posit that preserving residual urine volume should be viewed not merely as a physiological parameter but as a vital patient-centered outcome. The study suggests that strategies aimed at maintaining residual urine volume may support improved patient well-being by reducing the burden of strict fluid restriction, minimizing ultrafiltration needs, and potentially alleviating uremic symptoms.

The paper modestly acknowledges its limitations, noting that the cross-sectional design precludes causal inference and that the single-center, ethnically homogeneous sample may limit generalizability. Consequently, the authors call for future longitudinal studies to clarify the temporal relationships and causal nature of these associations, rather than proposing immediate clinical interventions based solely on these findings.

The Story of the "Leftover" Water

What They Found

Why This Matters (And What It Doesn't Say)

Technical Summary: Residual Urine Volume and Quality of Life in Maintenance Hemodialysis

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