What Is Oliguria and Anuria?

Reviewed on 3/19/2021
Oliguria and anuria are signs that kidney function is declining or not up to the mark.
Oliguria and anuria are signs that kidney function is declining or not up to the mark.

Oliguria and anuria are signs that kidney function is declining or not up to the mark.

Oliguria:

  • Oliguria or hypouresis means not enough urine is produced by the kidneys. It is also called a low output of urine.
  • It is clinically classified as a urine output of more than 80 mL/day but less than 400 mL/day.
  • In infants and children, oliguria is defined as a urine output of less than 1 mL/kg/h and less than 0.5 mL/kg/h, respectively.
  • Oliguria can be caused by any factor that affects renal (kidney) function or the free passage of urine down the urinary tract.
  • Oliguria occurring commonly in hospitalized patients is usually secondary to impaired renal perfusion (reduced blood supply to the kidneys) and is often predictable. The elderly and more unwell patients, for example, those in critical care settings, are the most at risk. The presence of oliguria reflects the severity of the underlying disease processes.
  • Common causes may include:

Anuria:

  • Anuria represents an absence of urine. It is a more extreme reduction than oliguria (hypouresis).
  • Anuria, sometimes called anuresis, is non-passage of urine; in practice, it is defined as the passage of less than 100 mL of urine in a day.
  • It is often caused by a failure in the function of the kidneys.
  • It most commonly occurs in men as a consequence of bladder outlet obstruction from an enlarged prostate.
  • It can also occur in patients who have a single functioning kidney, which then becomes obstructed or loses its blood supply.
  • It may also occur because of some severe obstruction such as kidney stones or tumors.
  • It may occur with end-stage renal disease.

What is renal failure?

Renal or kidney failure is a condition in which the kidney is unable to perform its function properly. This condition may be temporary or permanent. There are two different types of kidney failure:

  1. Acute kidney injury: It may start suddenly and may be reversible. It may occur due to injury, infections, medication side effects, or pre-existing diseases.
  2. Chronic/severe kidney disease: It progresses slowly over at least 3 months and can lead to permanent kidney failure. It may be caused by various medical conditions including diabetes, high blood pressure, and hereditary kidney disease. It usually does not give any symptoms until it progresses to advanced stages.

Stages:

  • Stage 1: 90% kidney function is usually preserved.
  • Stage 2: 60-89% kidney function is preserved.
  • Stage 3: Symptoms may include tiredness, puffiness, changes in appetite, dull back pain, and urine changes. Kidney functioning may be reduced to 40-59%.
  • Stage 4: Patients experience fatigue, swelling, changes in appetite, back pain, changes in urine, hypertension, and slowed digestion. Kidney function may be reduced to 15-29%.
  • Stage 5: It is end-stage kidney failure. The kidneys are only functioning at 10-15%.

The early stages of renal failure are usually treated by lifestyle modifications and controlling underlying causes such as hypertension and diabetes.

When kidney function falls below 10% of normal, the following options may be used:

  • Dialysis: It is a way to pump blood through a machine that filters out the waste and returns the blood to the body. There are two types of dialysis:
  • Kidney transplant: It is a procedure in which a surgeon replaces the kidney of a patient with kidney disease with that of a healthy person. A kidney transplant is the best way to treat many patients with end-stage kidney failure. The kidneys for a transplant come from people who have agreed to donate their kidneys when they die (deceased donors) or donated by healthy people (living donors). Living donors are most often family members of the patient. There is a shorter wait time to surgery for a transplant from a living donor. (This is because there is a waiting list for kidneys from deceased donors and not enough donors.) Additionally, patients with the kidneys donated by living donors live longer (and the kidneys last longer) than those with kidneys from deceased donors or who just stay on dialysis.

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References
Kidney failure: https://www.kidneycareuk.org/about-kidney-health/conditions/kidney-failure/

Differential Diagnosis in Primary Care, 4th Edition Anuria and Oliguria: https://doctorlib.info/medical/diagnosis-primary-care/15.html

https://emedicine.medscape.com/article/983156-overview

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