Your kidneys are essential for keeping your body humming. They balance fluids and get rid of waste. Typically, a healthy adult will pee out about 800 to 2,000 milliliters (mL) of urine daily, which breaks down to about 0.5 mL per kilogram of body weight each hour.
But sometimes, things go wrong. When you don’t pee enough, doctors call it “oliguria.” That’s usually less than 400 mL a day. And if you’re not peeing at all, or less than 100 mL a day, it’s called “anuria.” Both oliguria and anuria are signs that something might be wrong with your kidneys.
Keep in mind that neither oliguria nor anuria is a disease in itself, but rather a symptom of an underlying issue. This article will define oliguria and anuria, explore potential causes, associated symptoms, and available treatments, and address some frequently asked questions about these conditions.
Defining Oliguria: Reduced Urine Output
Oliguria is a condition in which you’re not producing enough urine. What counts as “enough” depends on whether you’re an adult, an infant, or a child:
- Adults: less than 400 mL per day
- Infants: less than 1 mL/kg/hour
- Children: less than 0.5 mL/kg/hour
When you have oliguria, it means your kidneys aren’t working as they should to filter waste out of your blood. Keep in mind that oliguria is a symptom of an underlying problem, not a disease in itself.
What’s “normal” urine output?
To give you some context, here are typical urine output ranges:
- Adults: 800 to 2000 mL per day
- Infants: 750mL per day
- Children: 1000 to 1500mL per day
Causes of Oliguria
Oliguria can stem from a few different issues. Doctors usually divide the causes into three main categories: prerenal, renal, and postrenal.
Prerenal Causes: Reduced Blood Flow to the Kidneys
Prerenal causes are all about things that cut down on the amount of blood getting to your kidneys. If your kidneys aren’t getting enough blood, they can’t do their job properly.
Some common prerenal culprits include:
- Dehydration (which can happen if you lose more than 20% of your body fluids)
- Reduced blood flow due to things like bleeding, heart failure, or sepsis
- Shock
- Certain metabolic conditions like hyperosmolar hyperglycemic nonketotic syndrome (HHNS), diabetic ketoacidosis (DKA), or pre-eclampsia
Renal Causes: Kidney Disease or Damage
Renal causes, on the other hand, involve direct damage or disease affecting the kidneys themselves. It’s like the kidneys are having trouble doing their job because they’re not working right.
Common renal causes can be:
- Congenital kidney disorders
- Autoimmune diseases
- Infections
- Trauma
- Certain medications
Postrenal Causes: Obstruction of Urine Flow
Postrenal causes are all about blockages in the flow of urine. The kidneys are working fine, but the urine can’t get out properly.
Some common postrenal causes are:
- Urinary obstructions like stones, tumors, or an enlarged prostate
- Urinary retention
- Inflammation of the urinary tract
What are the symptoms of oliguria?
Oliguria can cause a range of symptoms, depending on its underlying cause. If you’re experiencing any of the following, see a doctor:
- Urinating far less than usual
- Dark-colored urine
- Blood in your urine
- Pain
- Swelling, especially in your legs, ankles, or feet
- Low blood pressure
- Rapid heart rate
- Shortness of breath
- Severe fatigue
Getting a diagnosis is important. To determine the cause of oliguria, your doctor may order urine tests, blood tests, or imaging studies.
How is oliguria treated?
The first step in treating oliguria is figuring out what’s causing it. You and your doctor will then work together to treat the underlying condition.
Some common approaches include:
- Rehydration: If you’re dehydrated, your doctor will likely want to increase your fluid intake, possibly through IV fluids.
- Medication: If your oliguria results from an underlying disease, your doctor may prescribe medications to manage that condition.
- Surgery: Blockages in the urinary tract may require surgery to correct.
- Dialysis: In severe cases of kidney dysfunction, dialysis may be necessary to filter waste from the blood.
It’s important to treat oliguria quickly to prevent it from worsening and leading to further kidney damage or anuria.
Anuria: No Urine Output At All
Anuria is diagnosed when a person stops producing urine altogether, or when they’re only producing less than 100 mL each day.
Anuria is an indication of serious kidney problems. Because the kidneys aren’t filtering out toxins and waste products, those substances quickly begin to build up in the body.
Anuria compared to oliguria
It’s important to remember that anuria is a more critical condition than oliguria.
While oliguria is a sign that the kidneys aren’t functioning as well as they should, anuria is a sign that they’ve essentially stopped working altogether. Anuria requires immediate medical attention.
What causes anuria?
Like oliguria, the causes of anuria can be grouped into three main categories: prerenal, renal, and postrenal.
Prerenal causes
Prerenal causes are related to blood flow before it reaches the kidneys. Examples include:
- Severe dehydration that leads to hypovolemic shock
- Profound heart failure that significantly reduces blood flow to the kidneys
Renal causes
Renal causes stem from problems within the kidneys themselves, such as:
- Acute kidney injury (AKI) caused by severe infections or toxins
- End-stage renal disease (ESRD), where the kidneys have completely stopped working
Postrenal causes
Postrenal causes involve blockages after the urine leaves the kidneys, such as:
- Complete blockage of both ureters, perhaps by stones or tumors
- A ruptured bladder or urethra that prevents urine from being excreted
Symptoms and Diagnosis of Anuria
The main symptom of anuria is that you don’t pee. At all.
But you may also notice symptoms related to the underlying cause of your lack of urine production:
- Swelling (edema) from fluid retention
- Nausea and vomiting from toxins building up in your body
- Confusion and other mental changes caused by electrolyte imbalances
Doctors diagnose anuria by figuring out why you aren’t producing urine. They’ll likely perform a physical exam, and if you can pee even a little bit, they’ll order urine tests. They’ll also order blood tests and imaging scans.
How is anuria treated?
Anuria is an emergency that requires immediate medical care. If you’re not producing urine, you need to see a doctor right away.
Treatment usually involves:
- Identifying and treating the root cause of the anuria (for example, relieving a blockage or fighting an infection).
- Using dialysis to filter toxins and excess fluids from the blood.
Doctors will also work to prevent complications like electrolyte imbalances and fluid overload.
Anuric vs. oliguric: What’s the difference?
The key difference between oliguria and anuria is the amount of urine your body produces.
- Oliguria means you are producing less urine than normal.
- Anuria means you aren’t producing any urine at all.
Because your body isn’t eliminating waste products, anuria is much more dangerous than oliguria and requires immediate medical attention. If you aren’t producing urine, something is seriously wrong.
Both conditions share some potential causes and complications. But the severity of anuria means that doctors will treat it as a medical emergency.
To Conclude
Oliguria and anuria are both red flags for kidney problems. If your kidneys aren’t producing enough urine, that’s a sign that something isn’t working the way it should.
That’s why it’s so important to get a diagnosis and treatment right away. Finding out what’s causing the problem and treating it quickly can help prevent serious complications.
If you notice that you’re not urinating as much as usual, or if you’ve stopped urinating altogether, please see a doctor as soon as possible.