Flank pain describes back discomfort located on one or both sides of the spine between the lower edge of the rib cage and the upper border of the pelvis. When flank pain occurs on both sides, it often resembles a backache. Flank pain develops in association with a variety of kidney conditions and diseases because this is the location of the kidneys. As kidney-related causes of flank pain are potentially serious, contact your doctor without delay if you experience discomfort in this area of your back.
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A kidney infection, also known as pyelonephritis, is a leading cause of flank pain. With this condition, bacteria that initially infects the bladder travels upstream to infect the kidney(s). Urinary tract infections, including kidney infections, are more common in women than men. Pregnancy increases the risk for pyelonephritis should bacteria gain entry into the urinary tract. Aching flank pain associated with a kidney infection usually begins suddenly, persists and is accompanied by fever, chills, abdominal pain, and nausea and vomiting as well as urinary urgency, frequency and painful urination.
A stone is another common cause of kidney-related flank pain. Kidney stones form when chemicals normally dissolved in the urine form solid crystals that coalesce and grow in size. Flank pain associated with a kidney stone develops when urine flow from the kidney to the bladder is blocked. The pain typically begins suddenly, comes in waves and becomes increasingly severe over time to the point of excruciating intensity. In fact, a kidney stone is one of the most painful conditions a person can experience. The sharp flank pain often radiates into the abdomen and/or the scrotum or labia. Accompanying signs and symptoms include pink or bloody urine, nausea and vomiting. In some people, flank pain due to a kidney stone is more mild and intermittent, particularly if the obstruction of urine flow develops gradually. Men are more likely to develop a kidney stone than women.
Other Kidney Disorders
A number of other kidney disorders can trigger flank pain, although they are less common than pyelonephritis and kidney stones. Other possible kidney-related causes of flank pain include:
- Traumatic kidney injury
- Kidney tumor or cyst(s)
- Narrowing, malformation or malfunction of the ureter (the tube that carries urine from the kidney to the bladder)
- Blood clot in the ureter
- Kidney abscess
- Papillary necrosis (death of kidney tissue where urine flows into the ureter)
Not all pain in the flank area of the back is caused by an underlying kidney disorder. Muscle strains and nerve- or spine-related back problems are commonly to blame. Lack of other symptoms is a key feature of musculoskeletal flank pain. Conditions arising from other organs can also refer pain to the flank area of the back, including:
- Pulmonary embolism (a blood clot in the lung)
- Ectopic pregnancy (pregnancy outside the uterus)
- Gallbladder inflammation or obstruction
- Bowel obstruction
- Peptic ulcer disease
- Abdominal aortic aneurysm (ballooning of the aorta, the largest artery of the body)
Warnings and Precautions
Because many conditions and diseases can cause flank pain, it's important to see your doctor as soon as possible to determine the underlying cause and appropriate treatment. Seek urgent medical care if you develop flank pain and are pregnant. Urgent medical care is also needed if your pain is severe or you experience any warning signs or symptoms that might indicate a serious underlying cause, including:
- Sudden difficulty breathing or shortness of breath
- Chest pain
- High fever
- Shaking chills or cold, clammy skin
- Dizziness, lightheadedness or fainting
- Severe or worsening abdominal pain
Reviewed and revised by: Tina M. St. John, M.D.