What to know about oliguric renal failure

Oliguria and renal failure

“Oliguria” is the medical term for low urine output. It refers to a urine output that is lower than 400 milliliters (mL) per day or less than 20 mL per hour. The condition typically indicates a problem with kidney function.

Oliguria can occur due to pre-renal, intrinsic renal, and post-renal impairments.

ARF can affect the kidneys in each of these forms.

• Pre-renal ARF: This form of ARF involves a decrease in blood flow to the kidneys, which prevents them from functioning as usual. This may lead to oliguria. Potential causes of pre-renal ARF include low blood pressure and heart failure.
• Intrinsic renal ARF: This form of ARF can occur when medical conditions or certain medications damage the filtering units of the kidneys, called nephrons. When the nephrons cannot function properly, urine output may become lower.
• Post-renal ARF: Post-renal ARF typically occurs as a result of an obstruction that prevents urine from exiting the kidneys. Causes include an enlarged prostate, tumors, and kidney stones.

The oliguric phase of ARF is one of four broad clinical phases of the condition. The phases are:

1. Onset: In this phase, the pre-renal, intrinsic renal, or post-renal cause of the ARF occurs. This phase can last from a few hours to several days.
2. Oliguric: In the oliguric phase, urine output decreases to less than 400 mL per day. This phase can begin within 1 to 7 days of kidney injury and typically lasts for 10 to 14 days but may last several months.
3. Diuretic: During the diuretic or polyuria phase of ARF, a person’s urine output increases significantly. In this phase, a person usually urinates between 1 to 3 liters per day and may have an output as high as 5 liters daily. This may last 1 to 3 weeks.
4. Recovery: During the recovery phase, the kidneys begin to stabilize and function effectively. A person may notice an improvement within 1 to 2 weeks, but full recovery can take up to 12 months.

Anyone who experiences oliguria that does not resolve after drinking more fluids should contact a doctor.

Anuria and renal failure

Anuria refers to a complete absence of urine output or a minimal output of less than 100 mL per day.

The underlying causes of pre-renal, intrinsic renal, and post-renal forms of ARF can also lead to anuria. These include:

• a vascular blockage, which prevents adequate blood flow to the kidneys
• acute glomerulonephritis, an inflammation of the glomeruli, which are filters in the kidneys
• acute urinary tract obstruction, a blockage in the urinary tract that prevents urine from leaving the kidneys

Anuria is a medical emergency and typically occurs during the later and more severe stages of ARF. Anuria may be life threatening and requires immediate medical treatment.

Other signs of renal failure

Signs and symptoms of renal failure may also include:

• dark-colored urine
• swelling in the lower limbs
• skin rashes and itching
• nausea
• pain or pressure in the chest
• shortness of breath
• confusion
• loss of consciousness
• seizures

Doctors use different criteria to define the stages of renal failure.

To determine the stages, doctors will assess a person’s test results for:

• Creatinine levels: Creatinine is a kidney waste product, and higher-than-usual levels may indicate a problem with kidney function.
• Glomerular filtration rate (GFR): GFR can reveal how effectively the kidneys are able to filter waste. A decrease in GFR could indicate kidney impairment.
• Urine output: A decrease in urine output could indicate a problem with kidney functioning.

One set of criteria doctors use is the five categories of impairment and renal outcomes in RIFLE:

1. Risk: A person has an increase of 1.5 times their baseline creatinine level, their GFR decreases by 25%, or their urine output is less than 0.5 milligrams per deciliter (mg/dL) per kilogram (kg) per hour (h) for 6 hours.
2. Injury: A person’s creatinine is 2 times their baseline level, their GFR decreases by 50%, or their urine output is less than 0.5 mg/dL/kg/h for 12 hours.
3. Failure: Creatinine is 3 times a person’s baseline, GFR decreases by 75%, or the urine output is less than 0.5 mg/dL/kg/h for 12 hours.
4. Loss: Loss of kidney function over 4 weeks.
5. End-stage renal disease (ESRD): Loss of kidney function for over 3 months.

Treatments for renal failure

Treatments for renal failure differ depending on the cause and severity of the condition.

Some people with renal failure may require hospitalization.

Treatments for renal failure can include:

• increasing fluid intake
• stopping the use of certain medications
• taking antibiotics to treat infection
• using a urinary catheter to drain the bladder if there is an obstruction
• undergoing dialysis treatment to filter waste from the blood

Outlook

The outlook for people with ARF differs depending on the cause and severity of the condition and other factors.

Many people with ARF make a full recovery, especially when they receive early treatment for the underlying cause of the condition.

Some people may experience irreversible kidney damage, or repeated ARF, which can lead to poorer outcomes.

Other factors that contribute to poorer outcomes include:

• older age
• sepsis
• low blood pressure
• use of diuretics
• oliguria

Oliguria that persists for longer than 12 hours can worsen the outcome of ARF and may result in a higher risk of mortality.

A person with ESRD may live a long, healthy life with regular dialysis or after receiving a kidney transplant. However, 20% to 50% of people with ESRD die within 2 years.

Summary

Oliguria is a low urine output and often indicates kidney impairment. Oliguric renal failure refers to oliguria that occurs during acute renal failure (ARF).

There are various potential causes of oliguric renal failure, such as an obstruction in the urinary tract, a restriction of blood flow to the kidneys, and kidney damage from a medical condition.

The treatment and outcome for oliguric renal failure differ depending on the underlying causes and severity of the condition, and other factors.