We discuss and compare two different forms of urination problems: oliguria vs anuria.
First, we will define what they both are and how they compare. Then we’re detaining the similarities, differences, symptoms, treatment, and other important features of each.
Oliguria vs anuria
In the following sections, we share a detailed comparison of oliguria vs anuria.
Let’s start by reviewing the definition of oliguria and anuria.
Simply speaking, anuria is the medical term for not producing any urine at all. Oliguria is also a medical term referring to a lower urine output than normal.
Technically speaking, we talk of oliguria when you produce less than 400 mL of urine per day or less than 20 mL per hour.
Anuria is easier to define because it simply means not producing any urine at all. But you could still produce a minimal urine volume, and anuria will still be considered if the volume is lower than 100 mL a day.
Various problems can cause oliguria and anuria. For example, an autoimmune disease working against your kidneys, glomerulonephritis, and kidney dysfunction caused by toxins.
There are three types of causes:
- Prerenal (congestive heart failure, pulmonary embolism, myocardial infarction, thrombosis, thromboembolism, dehydration)
- Renal (acute tubular necrosis, glomerulonephritis, toxins)
- Postrenal (urinary tract obstruction and bladder outlet obstruction, such as benign prostatic hyperplasia).
Differences between oliguria and anuria
If you compare anuria vs oliguria, there are striking differences. Oliguria and anuria can be triggered by acute kidney injury, but their definitions differ.
The former features a urinary output lower than 400 mL per 24 hours. The latter is less than 100 mL per day.
You can say that anuria is a more advanced stage of oliguria. It is a more severe sign of kidney disease, and it is usually found in patients with acute kidney injury because nobody would survive many weeks urinating a volume lower than 100 mL per day.
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Anuria and oliguria are not only similar names. They also share common features, including their pathophysiology.
Acute and chronic renal failure are kidney insufficiency problems that reduce the glomerular filtration rate.
They can cause oliguria, which turns into anuria in the late stage of the disease, or as a complication.
That’s why oliguria and anuria are studied in the same medical textbook chapter because they are linked to the same conditions.
Depending on the location of the problem, these health problems can affect the blood flow to the kidneys (prerenal causes), kidney function (renal causes), or the flow of urine that leaves the kidneys (postrenal causes).
Since the kidneys are not working as intended, their function becomes impaired. This can lead to metabolic acidosis, an imbalance of serum electrolytes, and other complications that result from disease progression.
The prognosis of oliguria and anuria is also similar. However, since anuria is a more severe manifestation of kidney problems, the prognosis is naturally worse.
In both cases, mortality is around 10 to 35%, depending on the causes and complications of acute kidney injury.
And in chronic cases, the prognosis will be total kidney failure and cardiovascular disease if left untreated.
How to know which one you have
When you understand the differences between anuria vs oliguria, at least theoretically, it is easier to know which one you have.
Not urinating at all in 24 hours means you have anuria. Urinating a volume lower than 100 mL per 24 hours is anuria, too.
And if you void more than 100 mL and less than 400 mL of urine per 24 hours, that’s oliguria.
However, if you have acute oliguria, you might not realize immediately that urine output is reduced. And even if you do, measuring precisely how much urine you’re eliminating will probably take a lot of work.
Depending on the precipitating factor, you may have other symptoms to consider. For example, fatigue in congestive heart failure, blood in the urine in patients with glomerulonephritis, and rectal pain or weight loss in advanced prostate cancer.
Identifying the cause of anuria and oliguria
If you want to identify the cause of anuria and oliguria, you might want to take a look at other signs and symptoms. For instance:
- Cardiorenal syndrome: When impaired heart function causes anuria and oliguria, other symptoms may include fatigue, chest pain, shortness of breath, low blood pressure levels, and fluid buildup in the feet or the abdomen.
- Hepatorenal syndrome: If the fluid problem is associated with liver dysfunction, other symptoms may include jaundice, dark-colored urine, mental confusion, nausea, and vomiting.
- Abdominal compartment syndrome: This is a severe organ dysfunction syndrome that causes abdominal pain, difficulty breathing, swollen feet, and low blood pressure.
- Nephrotoxins: You may also need to rule out drugs that affect your kidneys, especially if you take multiple medications simultaneously. The main symptom here is having low urinary output closely after starting a new medication.
- Rhabdomyolysis: In some cases, your muscles start to break down, and the substances they release harm the kidneys. In these patients, the main symptoms are muscle cramps and pain, muscle weakness, and dark-colored urine.
- Benign prostatic hyperplasia and prostate cancer: These are common causes of oliguria, especially in senior males. In these cases, other symptoms appear progressively before oliguria and anuria ensue, including more frequent urination, slow urinary stream, urinary strain, urinary urgency, and dribbling at the end of voiding.
- Kidney stones: They can also trigger acute oliguria and anuria due to urinary retention. Other symptoms of kidney stones include blood in the urine, burning pain when you urinate, and flank pain.
Treating oliguria and anuria is fundamental to preserving kidney function. However, the etiology plays an integral part in the treatment.
Treating hypovolemia due to dehydration won’t be the same as treating for pulmonary embolism, interstitial nephritis, or an organ dysfunction syndrome.
The easiest treatment is perhaps that of postrenal causes of anuria and oliguria. For instance, urinary retention can be easily reversed by placing a Foley catheter or irrigating in case of a clogged catheter.
Other treatment options in hospitalized patients and the intensive care unit include:
- Hemodynamic stabilization: This is an important step in patients with inadequate hydration status and electrolyte imbalances. It means providing fluids calculated depending on the patient’s needs, which can be accompanied by electrolyte management. To avoid volume overload, doctors will administer fluids until reaching 60-75 mmHg of mean arterial pressure.
- Diuretic therapy: Diuretics stimulate the kidneys to start working and are useful in case of renal causes of anuria and oliguria. After a furosemide stress test, doctors will know how sensitive the patient is to diuretics and calculate the right dose for them.
- Renal replacement therapy: When patients can’t reach the target urine output with diuretic therapy, renal replacement therapy is recommended. This broad term includes hemodialysis, kidney transplant, and other measures to replace the filtrating function of the kidneys when they are not working as they should.
In this article, we have compared anuria vs oliguria, from their definition to their similarities, diagnostic procedures, treatment options, and more.
In a nutshell, oliguria is a lower urinary output than normal, and anuria means not urinating at all or having a minimal volume.
They are similar because both are associated with a lower urinary output than normal. Their main differences are the urinary volume related to each and that anuria is considered a more severe symptom than oliguria.
Oliguria and anuria are both symptoms of kidney disease, which can be due to prerenal, renal, or postrenal causes.
Prerenal causes are located before kidney function occurs, for example, in patients with dehydration, congestive heart disease, and pulmonary embolism.
Renal causes are triggered by kidney dysfunction that reduces urine production, such as glomerulonephritis.
Postrenal causes include urinary retention, benign prostatic hyperplasia, prostate cancer, and any obstructions that impair urine collection.
Treatment of these symptoms depends on the etiology. The first step in patients with postrenal causes is placing a urinary catheter.
When this doesn’t work, patients can go through diuretic therapy. If that doesn’t work, either, hemodialysis and other kidney replacement therapy options should be considered.