What is the normal urine output per hour?

From the Guidelines

Normal urine output for adults typically ranges from 0.5 to 1 milliliter per kilogram of body weight per hour, as defined by the most recent guidelines from the Kidney Disease: Improving Global Outcomes organization 1. This means that for an average 70 kg adult, normal hourly urine output would be approximately 35-70 milliliters per hour. Maintaining this output is essential for proper kidney function and fluid balance in the body. Some key points to consider include:

• Urine production below 0.5 mL/kg/hour may indicate dehydration, kidney dysfunction, or other medical issues requiring attention, as noted in the KDIGO clinical practice guidelines 1.
• Conversely, urine output significantly above 1 mL/kg/hour might suggest excessive fluid intake, certain medications, or conditions like diabetes insipidus.
• The kidneys regulate urine production based on the body's hydration status, blood pressure, and electrolyte balance.
• Clinicians often monitor hourly urine output in hospitalized patients as a key indicator of kidney function and overall fluid status, particularly in critically ill patients or those receiving intravenous fluids, as discussed in the context of acute kidney injury diagnosis and management 1. It's also worth noting that the definition and staging of acute kidney injury (AKI) have evolved over time, with the KDIGO guidelines providing a widely accepted framework for diagnosis and classification 1. However, the most recent and highest quality study, which is the 2022 AGA clinical practice update on the evaluation and management of acute kidney injury in patients with cirrhosis 1, supports the definition of normal urine output as 0.5 to 1 milliliter per kilogram of body weight per hour.

From the Research

Normal Urine Output

The normal urine output per hour can vary depending on several factors, including age, sex, and body weight.

• According to a study published in 2009 2, healthy males produce a mean urine output of 83 ml per hour during the day and 48 ml per hour during the night.
• However, other studies have focused on the definition of acute kidney injury (AKI) and its relation to urine output.
• For example, a study published in 2021 3 defines AKI as a decrease in urine output to less than 0.5 mL/kg/hour for 6 hours.
• Another study published in 2013 4 suggests that a 6-hour urine output threshold of 0.3 ml/kg/hour is associated with a stepped increase in in-hospital mortality or dialysis.

Urine Output Thresholds

Different studies have proposed various urine output thresholds for the diagnosis of AKI.

• A study published in 2022 5 found that higher urine output thresholds (1.5 or 2 ml/kg per hour) may better discriminate neonatal mortality in very preterm infants.
• In contrast, a study published in 2021 6 suggests that calculating hourly urine output using actual body weight may lead to overestimation of AKI in obese patients.
• The optimal urine output threshold may depend on the duration of urine collection, with shorter collection intervals potentially requiring lower urine output thresholds 4.

Factors Affecting Urine Output

Several factors can affect urine output, including:

• Age: Urine production and voiding diary parameters depend significantly on age 2.
• Body weight: Urine output thresholds are often indexed to body weight, but the use of actual body weight versus ideal body weight may affect AKI diagnosis 6.
• Sex: Urine production and voiding diary parameters may differ between males and females, although the provided studies primarily focus on male populations 2.
• Volume status: Fluid balance and volume status can impact urine output, with hypovolemia potentially leading to decreased urine production 3.