Renal failure means that your kidneys aren’t working as they should. Acute renal failure is often sudden and usually reversible. Chronic renal failure means that you’ve lost kidney function over time.

You want the kidneys to be at their best. They’re responsible for filtering wastes and keeping fluid balance in your body. Renal failure is when your kidneys aren’t working as they should.

Acute renal failure refers to short-term issues with kidney function. Doctors or healthcare professionals now use the term acute kidney injury (AKI) more often.

Chronic renal failure means your kidneys haven’t worked well for several months. In most instances, chronic kidney disease (CKD) and chronic renal failure mean the same thing. In some cases, chronic renal failure refers specifically to people who are in end stage renal disease (ESRD) or stage 5 CKD.

Keep reading to learn more about acute and chronic renal failure.

Doctors divide AKI causes into three categories: pre-renal, intrinsic, and post-renal.

Pre-renal causes

Pre-renal causes are cases where you don’t have enough fluid in your body or blood flow to your kidneys. Examples include:

Intrinsic causes

These are causes that affect your kidney’s ability to work. Sometimes pre-renal causes can lead to intrinsic causes if your kidneys don’t get enough blood and oxygen. Examples include:

  • reactions to medications such as nonsteroidal anti-inflammatory drugs or amphotericin B
  • reactions to contrast dye
  • lupus

Post-renal causes

Post-renal causes include anything that keeps blood or fluid from leaving the kidneys. Examples include:

  • large kidney stones
  • blood clots
  • tumor in or around the bladder

Causes of chronic renal failure

AKI can lead to chronic renal failure but not always. CKD often occurs because of the effects of one or more chronic conditions. Examples of these conditions may include:

Doctors will recommend closely managing these conditions to prevent progression to CKD.

AKI will usually cause symptoms that occur quickly. For doctors to consider renal failure a chronic condition, you must experience changes for about 3 months.

AKI doesn’t always cause a lot of visible symptoms. The most common symptom you may notice is a change in how much you pee. Your kidneys filter water and wastes in your body, so when they don’t work as well, you’ll likely pee less.

If you do experience symptoms, they may include:

A person with CKD may not show symptoms until their kidney function declines to less than 20%. At this time, symptoms will be similar to that of acute renal failure and may also include:

If left untreated, these symptoms can lead to ESRD, where your kidneys function at 10% or less of their typical level. Those with ESRD require dialysis or a kidney transplant to prevent deadly complications.

A creatinine test is the best way for doctors to assess your kidney function and confirm renal failure.

Creatinine is a waste product that your kidneys filter. If too much creatinine builds up in your blood, it might mean that your kidneys aren’t working well. If you’re peeing less, despite taking in about the same amount of fluid you usually do, a doctor may also suspect acute renal failure.

With time, AKI and CKD can both cause serious health complications. The kidneys filter not only fluids but also electrolytes such as potassium, calcium, and phosphorus. Too much potassium in your blood can harm your heart.

For this reason, untreated AKI and CKD can lead to symptoms such as:

  • abnormal heart rhythms (arrhythmia)
  • low blood counts (anemia)
  • fluid overload, which can cause you to have difficulty breathing

If these symptoms occur alongside an illness or injury, a doctor will usually suspect your kidneys aren’t working as expected.

To diagnose CKD, a doctor will have noticed signs of kidney damage for 3 months or more. They measure this using a glomerular filtration rate (GFR) test. This is a simple blood test that can assess your kidney function.

The formula health professionals use to calculate your GFR includes:

  • creatinine level
  • age
  • sex
  • race
  • body size (sometimes)

A lower GFR means weaker kidney function.

60 or higherYour kidneys are functioning at a typical level.
Below 60You may have CKD if this value holds for 3 months or more.
15 or lowerYou may have stage 5 CKD or ESRD.

The treatment for AKI is to address whatever is causing the failure. Some causes, such as dehydration and blood loss, can be reversible. Others, such as kidney damage from toxic medications or substances, aren’t reversible.

A doctor will often recommend a fluid challenge. This involves giving you a certain amount of fluids to see if your urine output increases. If pre-renal causes have led to acute renal failure, you’ll often “respond” and increase your urine output.

After a fluid challenge, a doctor will have you stop taking any medications that could harm your kidney. This includes avoiding the use of contrast dye.

Doctors may also prescribe the following treatments:

  • dialysis to remove excess fluid and electrolytes
  • continuous renal replacement therapy if you can’t tolerate dialysis
  • diuretics to prevent too much fluid buildup

The earlier you find and treat acute renal failure, the better your chances of preventing permanent damage.

For CKD, treatments often include treating underlying medical conditions such as high blood pressure and diabetes. In late stage CKD, where your kidneys are failing, you may need dialysis or a kidney transplant.

AKI is an underlying cause for about 1% of all hospital admissions in the United States. About two-thirds of all people in an intensive care unit experience acute renal failure.

Most people with AKI recover by treating the underlying cause. But some people may progress to CKD.

According to the National Kidney Foundation, about 37 million Americans have CKD. The most common cause of death among them is heart disease. This is likely because conditions such as high blood pressure can contribute to heart disease and chronic renal failure.

Acute renal failureChronic renal failure
Also known asacute kidney injury (AKI)chronic kidney disease (CKD)
Causeinjury, illness, or medicationunderlying chronic conditions
Onsetsuddengradual (months to years)
Symptomscome on quickly and can be very severemay not appear until kidney is severely damaged
Treatmenttreat underlying causetreat underlying condition in early stages;
dialysis or transplant in later stages
Outlookusually reversiblenot usually reversible

AKI and CKD are very distinct, but both can affect your health significantly. In the case of AKI, timely treatment is important to help prevent permanent damage and chronic failure.

If you have CKD, a doctor may recommend changes to how you manage an underlying chronic condition or dietary changes. CKD in its later stages means that your kidneys are failing. You may need dialysis or a kidney transplant.