Kidney Pain

Medically Reviewed on 6/28/2023

What are the kidneys?

Kidney pain and back pain can be difficult to distinguish.

The kidneys are two organs whose major functions are to remove waste products and excess fluid from the body and to produce hormones that regulate blood pressure, red blood cell production, acid regulation, and influence calcium, sodium, potassium, and electrolyte metabolism.

Each kidney contains around a million units called nephrons, each of which is a microscopic filter for blood. It's possible to lose as much as 90% of kidney function without experiencing any symptoms or problems.

Where are the kidneys located?

The kidneys are bean-shaped organs (about 11 cm x 7 cm x 3 cm) that are located against the back muscles in the upper abdominal area. They sit opposite each other on both the left and right sides of the body; the right kidney, however, sits a little lower than the left to accommodate the size of the liver.

What is the function of the kidneys?

The excess waste products and excess fluid are removed when the kidneys produce urine that is excreted from the body. Moreover, the kidneys play an important role in the regulation of the body's salt, potassium, and acid content.

The kidneys also produce hormones that stimulate the production of the following:

What are some kidney conditions and diseases that cause pain?

Many of the causes of kidney disease that lead to kidney pain (also termed flank pain) are due to acquired underlying diseases that may acutely or chronically affect kidney function. Other diseases are present at birth. Some people may be born with an abnormality that is genetically determined that affects the kidneys.

Kidney pain or flank pain can be acute, relatively constant, and sharp. This is termed "renal colic." This kind of pain is usually seen when a kidney stone or other problem blocks the tube (ureter) that drains the kidney. However, other processes can cause chronic dull aching with occasionally sharp kidney pain.

Some of the causes of kidney pain or flank pain are as follows:


Kidney Stones: Symptoms, Causes, and Treatment See Slideshow

What are the first signs and symptoms of kidney pain?

Symptoms associated with kidney pain (also termed renal or flank pain) are discomfort (acute or chronic), aches, or sharp pain that occurs in the back between approximately the lowest rib and the buttock. Depending on the cause of the pain, it may radiate down the flank to the groin or toward the abdominal area.

Some individuals may develop symptoms and signs such as:

Other symptoms and signs that may occur if kidney function is increasingly compromised include:

Depending on the underlying cause, kidney pain may occur on the left or right side. Sometimes it can occur on both sides of the back; traumatic kidney injury (kidney laceration) may cause the above symptoms, but mild damage may initially have no symptoms. Severe kidney lacerations can cause abnormal blood pressure and pulse, and shock.

Kidney pain itself is a symptom that may happen due to problems or diseases of the kidney or its associated structures, including the ureters or bladder. However, other diseases may mimic kidney pain, but are not actually due to the kidneys, for example:

Although kidney pain often occurs on one side of the back, it can occur on both sides at the same time and may radiate toward the abdomen or groin.

Pain that occurs suddenly is sharp, severe, and may increase and decrease in waves often due to kidney stones in the ureters of the kidneys. Pain caused by kidney stones is termed renal colic.

When should call a doctor for kidney pain?

Individuals should not postpone seeing a doctor about kidney pain or flank pain. Although flank pain is often seen in underlying problems with the kidney, many other diseases can mimic kidney pain, and a physician can help with an accurate diagnosis of underlying problems that result in kidney or flank pain. Any acute onset of intense kidney or flank pain should be evaluated immediately.

Warning signs that kidney disease is present and may result in kidney pain or flank pain are the following:

In addition, if an individual has diabetes or any of the congenital problems that lead to kidney dysfunction, the individual should be routinely checked for the onset of kidney dysfunction or kidney failure by their physician.

What procedures and tests diagnose kidney diseases?

The doctor usually will do a history and physical examination. Initial tests usually consist of a complete blood count (CBC), kidney function (creatinine and BUN), urine test, and when appropriate, a pregnancy test. A lacerated kidney may be suspected if the person has experienced a traumatic injury to the lower back.

If kidney stones are suspected, a CT exam (renal protocol or noncontrast spiral CT) or renal ultrasound is done; an abdominal X-ray (KUB) may be ordered but has been replaced in general by ultrasound and CT. As patients with kidney stones often need to repeat X-ray studies or have repeat episodes of kidney stones, ultrasound with its lack of radiation is a good study to consider.

Abdominal/pelvic CTs with contrast or magnetic resonance imaging (MRI) and aortogram may be ordered to further define or differentiate underlying kidney (renal) and nonrenal causes of flank pain. Such studies are routinely performed if a kidney is suspected to be damaged by a traumatic event (auto accident, gunshot wound, or blunt trauma such as from a collision in football or workplace injury).

What level of BUN indicates kidney failure?

The normal range of blood urea nitrogen (BUN) is between 7 and 20 mg/dL or 2.5 and 7.1 mmol/L. There may be slight variations between labs. A decline in kidney function can cause an increase in BUN levels. There is no definite value of BUN that would diagnose kidney failure.

BUN and creatinine tests can be used together to find the BUN-to-creatinine ratio (BUN: creatinine), which is more specific than the BUN test alone. More specific tests such as glomerular filtration rate (GFR) and creatinine clearance may be performed further to diagnose kidney failure.

A high BUN value may be due to reasons unrelated to the kidneys such as:

If your BUN values are consistently outside the normal limits, talk to your doctor to know the reason behind the variation.

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What is the treatment for kidney pain?

Kidney pain (flank pain) treatment depends on the underlying cause of the pain.

  • Kidney infections and kidney stones that cause pain are often treated with ibuprofen, ketorolac (Toradol), acetaminophen (Tylenol and others), or occasionally with small amounts of morphine (kidney stones). However, these agents treat pain (pain relief only) and not the underlying cause(s) of pain.
  • Some patients may spontaneously pass (urine sweeps the irritating kidney stone out of the ureters and/or urethra) small kidney stones (usually less than about 6 mm in diameter) and then be pain-free.
  • Infections like urinary tract infections (UTIs) and pyelonephritis usually require antibiotic treatments in addition to pain medications.
  • If kidney stones completely block a ureter or are about 6 mm in diameter or larger, they may require urologic surgery. Usually, recovery time is fast (same day or a few days) if kidney stones are removed by retrograde surgical techniques. However, some severe kidney lacerations may require more extensive surgery. Recovery time for these surgeries varies from weeks to months.
  • Other underlying causes of flank pain may need similar pain management and concurrent treatments. However, patients with known kidney problems (kidney disease) and/or renal function compromise should not be treated with pain medications that are either filtered (removed) through the kidneys and/or may cause further renal damage.

What is the prognosis of kidney pain?

The prognosis for someone with kidney pain depends upon the cause, and the majority of patients can have a good outcome when treated quickly and appropriately.

Can kidney pain be prevented?

Kidney pain can be prevented by avoiding those situations that are the underlying causes of kidney infection and/or kidney damage.

Medically Reviewed on 6/28/2023

Dave, C, MD, et al. "Nephrolithiasis." Medscape. Updated: Jan 15, 2020.

Gill, BC, MD, et al. "Causes of Flank Pain." Medscape. Dec 11, 2020.

"Pain in Kidney or Urine Diseases." 2020.

"How Your Kidneys Work." National Kidney Foundation. 2020.

"What Is Kidney (Renal) Trauma?" Urology Care Foundation. 2020.