What Is It, Causes, Signs and Symptoms, and More
Author: Maria Emfietzoglou, MD
Editors: Alyssa Haag, Józia McGowan, DO, Kelsey LaFayette, DNP, ARNP, FNP-C
Illustrator: Jessica Reynolds, MS
Copyeditor: Stacy M. Johnson, LMSW
What is oliguria?
Oliguria is the severe reduction of urine production and is defined as a urine output of fewer than 500 mL per day or less than 0.5 ml/kg/hour. It is usually a sign of an underlying disorder. A healthy individual produces between 800 and 2000 milliliters of urine daily, depending on their hydration level. If left untreated, oliguria can be life-threatening as it usually indicates decreased kidney function or urinary tract obstruction.
What is the difference between oliguria and anuria?
Oliguria occurs when urine production is reduced dramatically, defined as a decrease in urine output to less than 500 mL per day or less than 0.5 ml/kg/hour. In contrast, anuria is the absence of urine production, defined as a urine output of fewer than 100 milliliters per day.
What causes oliguria?
Oliguria can occur when there is an abnormal renal function, thereby causing a reduction in urine production or a blockage in the outflow of urine from the kidneys. If oliguria develops over a few hours or days, it is called acute kidney injury (AKI) or acute renal failure (ARF); if there is a gradual loss of kidney function, it is called chronic kidney disease.
Causes of oliguria can be broken into prerenal, intrarenal, and postrenal causes. Prerenal causes include anything that causes decreased blood flow into the kidneys, including hypovolemic states, such as a major hemorrhage; gastrointestinal losses, like diarrhea or vomiting; renal losses, such as with the use of diuretics or during osmotic diuresis in diabetic ketoacidosis; skin losses, like with severe burns; and sequestration of fluid—also known as third-spacing—which can occur in heart failure, liver disease, acute pancreatitis or sepsis. Reduced blood flow to the kidneys can also result from renal artery stenosis when one or both renal arteries become narrowed.
Next, intrarenal causes involve damage to the renal tubules, the glomerulus, or the kidney interstitium, which is the space between adjacent tubules. Ischemia, or loss of blood supply to the cells, and nephrotoxins (e.g., aminoglycosides; heavy metals, like lead; radiocontrast dye) can lead to acute tubular necrosis (i.e., necrosis of the epithelial cells of the renal tubules). Systemic disorders, such as certain infections or autoimmune conditions, like Sjogren syndrome, sarcoidosis, or systemic lupus erythematosus, can also cause intrarenal kidney damage.
Finally, postrenal causes can occur due to an outflow obstruction of urine from the kidneys. This most frequently occurs with benign prostatic hyperplasia or prostate cancer, both of which lead to compression of the urethra. Other causes include compression of the ureter by intra-abdominal tumors and kidney stones, which can become lodged in either the ureter or urethra.
What are the signs and symptoms of oliguria?
Oliguria is not a condition but rather a sign of an underlying disorder. It is a urine output of fewer than 500 mL per day or less than 0.5 ml/kg/hour. Accompanying signs and symptoms vary depending on the underlying cause. For example, individuals with shock may present with oliguria, tachycardia, hypotension, reduced skin turgor, and cool extremities. On the other hand, with obstructive ureteral kidney stones, the individual may experience extreme flank or abdominal pain. In addition, acute kidney failure, or acute kidney injury, leading to oliguria can result in various complications, including peripheral edema; hyperkalemia; severe metabolic acidosis; and signs of uremia (e.g., uremic pericarditis, uremic encephalopathy, coagulopathy), which occur when the kidneys are no longer able to remove waste products from the blood, and thus, can be life-threatening.
How is oliguria diagnosed?
Diagnosis of oliguria requires measuring the individual’s urine output, typically done via a urinary catheter, to allow for complete emptying of the bladder. A thorough physical exam may follow. Once oliguria is established, further diagnostic tests will depend on the differential diagnosis of the underlying cause. A basic metabolic panel, which includes BUN, estimated glomerular filtration rate (eGFR), and serum creatinine, may also help determine the etiology and severity of renal dysfunction. A urinalysis can also help to identify whether the injury is acute or chronic. An abdominal ultrasound can identify the presence of proximal ureter stones and hydronephrosis (i.e., swelling of one or both kidneys due to a build-up of urine). Finally, a CT scan of the abdomen and pelvis without contrast can help identify abdominal tumors or stones along the urinary tract.
How is oliguria treated?
Oliguria is a condition that requires prompt diagnosis and treatment. Management of oliguria depends on the cause. With prerenal and intrarenal causes, treatment aims to manage the body’s fluids while the kidneys recover carefully. In contrast, with postrenal causes, treatment relies on removing the obstruction to allow the urine to flow as usual. Individuals with end-stage kidney disease, or those with severe acute kidney injury with signs of uremia, are usually critically ill and are managed in the intensive care unit. Depending on the individual, they may require renal replacement therapy, which may include dialysis or a kidney transplant.
What are the most important facts to know about oliguria?
Oliguria refers to the decreased production of urine, defined as a urine output of less than 500ml per day or 0.5 ml/kg/hour. Causes of oliguria include acute kidney injury and chronic kidney disease. Kidney dysfunction can also be classified into prerenal, which includes hypovolemic states, third-spacing, and renal artery stenosis; intrarenal, which includes acute tubular necrosis and systemic disorders; and postrenal kidney dysfunction, including prostatic disorders, tumors, and kidney stones. Diagnosis involves measuring urine output via a urinary catheter and other tests, including a basic metabolic panel, urinalysis, abdominal ultrasound, and CT scan to identify the cause. Treatment may include managing the underlying cause of kidney injury.
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