When to See a Doctor. People will often assume that sudden flank pain is caused by a pulled muscle or overexertion, and, in many cases, it will be. If the pain persists, worsens, or is accompanied by urinary symptoms or signs of infections, you should see your doctor as soon as possible.
Kidney pain, also known as renal pain, is caused by the injury, impairment, or infection of the kidneys. The kidneys are a pair of bean-shaped organs situated on either side of the spine that are responsible for filtering blood and maintaining the correct balance of fluids and electrolytes in the body. The pain may be described as dull and throbbing or sharp and severe depending on the underlying cause. While kidney pain is sometimes mistaken for back pain, the sensation is far deeper and located higher on the upper back, just below the ribs.
Kidney pain can be classified as unilateral if one kidney is affected or bilateral if both kidneys are affected. This may provide a clue as to whether the problem is intrinsic (occurring within the kidneys), prerenal (related to an organ above the kidneys), or postrenal (related to obstruction or disorder below the kidneys).
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Causes
The causes of kidney pain are extensive and can be broadly characterized as either an infection, trauma, obstruction, or growth.
Kidney Infection
A renal infection, also known as pyelonephritis, is typically caused by bacteria and can affect one or both kidneys. Acute pyelonephritis is a type that strikes suddenly and severely, while milder, recurrent cases are referred to as chronic pyelonephritis. Pyelonephritis is usually caused by an infection that has spread from the lower urinary tract, including the ureters, bladder, or urethra.
Acute pyelonephritis can often develop over the span of two days. Symptoms include:
- Unilateral or bilateral kidney pain, often blunt and intense, felt in the flank (back and side), abdomen, or groin
- High fever (greater than 102 Fahrenheit)
- Body chills
- Nausea and vomiting
- Fatigue
- Confusion
- Painful or burning urination (dysuria)
- Cloudy or fishy-smelling urine
- Blood in urine (hematuria)
- A frequent need to urinate (urinary urgency)
Chronic pyelonephritis is experienced less intensely, and, in some cases, there may be no symptoms. If symptoms do develop, they may include a dull ache in the flank accompanied by malaise and a low-grade fever.
Kidney Trauma
Renal trauma is caused by either a blunt-force impact or a penetrating wound that lacerates one or both kidneys. Because of the kidneys’ vulnerable position in the abdomen, injuries like these are not uncommon.5 In fact, as many as 10% of abdominal injuries will sustain damage to the kidneys. Vehicle accidents, physical assaults, and severe falls account for the majority of renal traumas.
The challenge with these injuries is that they are not always overtly symptomatic. While some may present with pain, the pain may be dull rather than specific, and there may or may not be any signs of bruising or physical injury. With that being said, touching the kidney area will usually cause pain.
Other characteristic symptoms may include fever, hematuria, an inability to urinate (urinary retention), decreased alertness, rapid heart rate (tachycardia), and abdominal pain and swelling. Symptoms like these warrant emergency treatment.
Renal Obstruction
Renal obstruction can occur in the kidneys or as the result of urinary blockage downstream. Those that are intrinsic or affect the ureters may cause unilateral or bilateral pain. A blockage downstream in the bladder or urethra tends to impact both kidneys.
Also known as obstructive uropathy, the blockage may be caused by any number of conditions, including:7
- Kidney stones
- Bladder stones
- Urinary tract infection (UTI)
- Benign prostatic hyperplasia (enlarged prostate)
- Pregnancy
- Long-term catheterization
- Renal vein thrombosis (a blood clot in the kidney)
- Neurogenic bladder (nerve-related bladder weakness)
- Bladder, cervical, colorectal, prostate, or uterine cancer
- Vesicoureteral reflux (a congenital disorder in which the urine backflows into the kidneys)
When an obstruction occurs for whatever reason, the kidneys will begin to swell, a condition referred to as hydronephrosis. Symptoms include pain in the flank, groin, or abdomen alongside fever, dysuria, urinary urgency, and nausea.
The symptoms can vary by the location and severity of the obstruction. Kidney stones often cause the most pain, typically centered in the flank and radiating to the abdomen and groin in waves. Others are less specific but can worsen if the blockage is left untreated, leading to fever, sweating, chills, vomiting, hematuria, and diminished urine output.