Flank Pain

What is Flank Pain?

A common cause of discomfort in the body, this is a painful condition that is associated with the kidneys. It can be defined as a dull, continuous or spasmodic severe pain in the flank area. The pain is usually felt on one of the sides but it may even occur on both the flanks, originating from the lower back. It can occur on one side – unilateral, or both the sides – bilateral. This pain is characteristic of the development of other underlying ailments, mostly related with the kidneys.

Flank Pain Location

Flanks are the fleshy parts on the sides, located just above the pelvis, underneath the last ribs. Pain in flank area might be dull or sharp, usually spreading from the back.

Flank Pain ICD 9 Code

The ICD 9 code of flank pain is approximately 789.07. It comes in the category of “generalized”, “other symptoms involving abdomen and pelvis” and “abdominal pain”.

Flank Pain Causes

The causes of this ache have been enumerated below:

Renal disorders

Pain in flanks is one of the typical characteristics associated with kidney stones. The pain is sudden, which arises in the flanks and radiates to the groin in such cases. Polycystic kidney diseases, infection in the kidney, abscess and even kidney cancer may cause flank pan. These may be accompanied with fever, urinary problems and tiredness along with severe pain. Development of tumors in the kidney can lead to flank pain, especially when the tumors become large enough. The pain may result from the stretching of the renal capsule due to renal tumors.


This medical condition is characterized by moderate or dull ache in the flanks. One of the common reasons for pain in flanks, it leads to severe discomfort due to tenderness in the flanks and costovertebral angle.

Urinary Tract Infection (UTI)

UTIs might be caused in different age groups. When the infection engulfs the kidneys or urinary bladder, flanks start aching and cause difficulty while urinating. In this infection, renal abcesses occur as a complication. It mimics the symptoms of acute pyelonephritis, including fever and stomach pain apart from flank pain.

Abdominal aortic aneurysms (AAA)

Flank pain is noted in individuals suffering from AAA. Almost 10% of the patients of AAA might complain of this. It might imitate renal colic pain to some extent. Aneurysm might be a result of stretching or damage caused to the nerve plexus surrounding the celiac axis apart from some other structures which provide nerve supply to the kidneys.


This infection takes place due to varicella-zoster virus which leads to skin rash like chicken pox. It is also called Herpes zoster, one common symptom of which is pain in the flanks. Burning pain is usually felt in the flanks before the development of the skin rash.

Renal Papillary necrosis

Flank or back pain is common symptom of this disorder which is characterized by the death of the renal papillae. It is possible due to analgesic nephropathy apart from a range of other ailments like pyelonephritis, sickle cell anemia, rejection of kidney transplant and blocked urinary tract.

Injured back

Due to trauma in the flanks or back, dull pain can be sensed in the lumber and thoracic regions. It leads to aching muscles, which is aggravated by doing physical activities like bending or lifting. A healthcare professional can relieve the pain by injecting local anesthetic and administering heat pads and NSAIDs.


Another cause of side pain is Radiculitis which occurs due to an injury caused to the lumber thoracic nerve roots. Pain might appear to be like that of renal colic when it occurs in the 10th, 11th or 12th ribs.

Acute renal infarction

One of the typical symptoms of this condition is unilateral pain in the side accompanied by hematuria. This disorder afflicts both the kidneys of patients mostly who are above 60 years. It is often wrongly diagnosed as Pyelonephritis of acute renal colic due to the presentation of symptoms in the beginning.

Gynecological reasons

Presence of ovarian cysts, endometriosis and tubal pregnancy in women can lead to one-sided pain in the flanks.

Flank Pain Symptoms

Pain in sides is a symptom in itself, representing an array of diseases concealed in the body. Several underlying diseases of the kidney prompt the causation of varied symptoms apart from flank pain. Whereas, if kidney problem is not causing flank pain but it has resulted due to muscle spasm, other symptoms usually do not occur except muscle tenderness. For pain in sides caused due to renal tumors, blood in urine is one of the most common symptoms. Dull pain in the flanks is mainly a symptom of renal calculi. Some of the symptoms of side pain associated with kidney ailments are:

  • Fever
  • Chills
  • Blood in urine
  • Nausea
  • Vomiting
  • Abdominal pain
  • Difficulty in urination
  • Tenderness in abdomen.
  • Rash (indicating shingles)

These are some of the features of side pain which might be indicative of minor ailments:

  • Deteriorating flank pain while moving the body excluding the limbs
  • Tenderness in the muscles around the spine
  • Moderate pain in the flanks
  • Absence of any related symptoms

These are the features of side pain which might be indicative of major medical conditions:

  • Stabbing flank pain
  • Severe pain
  • Flank pain even without bodily movements
  • Pain from the flanks transcending to labia of the females and testicles of the males
  • Fever, vomiting and blood noted in the urine.

Left Flank Pain

Pain in the flank on left side may be due to varied diseases affecting an individual. Left sided flank pain can be persistent and mild or acute. Know about some main causes of left side pain:

  • Kidney disorders, urinary tract infections, muscle spasms, gastrointestinal diseases and diverticulitis as well as tumor located in the left kidney
  • Sexually transmitted disorders and testicular disorders
  • Pulmonary embolism, pancreatitis and herpes zoster infection are various other factors. This pain occurs in addition with tenderness in abdomen, fever and tachycardia or rapid pulse.
  • The right flanks usually ache due to appendicitis. However, this condition can also be the cause of aches in the left flanks on rare occasions.
  • Left lower side pain can be dull in nature. To diagnose its origin, a physician might conduct tests. In order to be sure about the intensity of the ailment, proper investigation is required.

Left Flank Pain after Eating

Pain in the left side after eating is often ignored. However, there can be some implications of this. Small intestines and colon may be responsible for generating this pain, which is often due to abdominal formation of gas. In case of inflammatory disorders of intestine like Diverticulitis, such pains may occur. Severe left flank pain may even signal colorectal cancer.

Left Flank Pain In Women

In women, several causes can be ascertained for pain in the left flanks, which include ectopic pregnancy and endometriosis. Some of the other causes of the unilateral pain are:

  • Ovulation: During ovulation, when the egg travels from the ovary, pain in the sides is common.
  • PCOS: Polycystic ovarian syndrome is yet another common disorder which may cause recurring pain in the left flanks.
  • Rupture of cysts: Ovarian cysts may rupture or become twisted, following which the flanks on both the sides can pain.

Chronic Flank Pain

Chronic flank pain should never be ignored as it might be indicative of degenerative ailments which affect the body. It may be a result of kidney stones, kidney tumors, kidney abscesses and colon disorders. Constipation can also cause chronic pain in the flanks. Chronic pain resulting due to severe ureteral blockage can lead to renal damage.

Intermittent Flank Pain

Intermittent flank abdominal pain can be due to renal colic. Shooting sporadic pain of this nature generally occurs when the stone blocks the ureter. Apart from kidney stones, it might be significant of other kidney disorders like pyelonephritis and kidney cysts. However, it might not be related with kidney failure. Without proper investigation, it would be wrong to suppose the pain to be caused by the kidneys alone. Gas or gall bladder stone can also be responsible for it. It is always wise to go for a medical checkup to diagnose your problem.

Flank Pain Diagnosis

For determining the correct cause of side pain, a series of tests might be done.

Physical examination

This is done to check:

  • Enlargement of the lymph nodes
  • Jaundice
  • Loss of weight
  • Pallor
  • Fever
  • Peripheral edema
  • Laboratory investigations include:

Hematology tests

These include:

  • Complete blood analysis: TLC, ESR count, Red blood cell count and hemoglobin.
  • Kidney function test: Serum creatinine and blood urea
  • Serum PTH levels
  • Blood culture
  • Serum calcium

Urinary Tests

These include:

  • Urine culture
  • Urine volume
  • Urine pH level


This involves:

  • Abdominal X-ray
  • Chest X-ray
  • Ultrasound of pelvic region and abdomen
  • Intravenous urogram

Specialized studies are also conducted with CT scans and MRI. CT scans are helpful in providing clear picture of tumors in the kidney and presence of metastasis. Diagnosis during pregnancy tends to be to be difficult owing to the physiological changes in the patients.

Flank Pain Differential Diagnosis

The differential diagnosis of this ailment involves a huge field. Some of the ailments include:

  • Appendicitis
  • Renal colic
  • Cholecystitis
  • Internal hernia

Flank Pain during Pregnancy

During ectopic pregnancy, the pain may initially engulf the sides and then gradually proceed to the pelvic region. Since the egg is implanted on the outer side if the uterus, with the growing fetus, lower abdomen starts paining. During normal pregnancy, urine flow can be obstructed due to the fetus which may even cause the kidneys to swell. To avoid complications like premature birth and kidney damage, it should be treated immediately. According to a study conducted on pregnant women, it was found that almost 90% of them complained of side pain. Diagnosis of renal colic is very difficult in pregnant women.

Flank Pain Treatment

Since flank pain is often significant of some other underlying disorder, it is treated by addressing the issue which is responsible for it. Some of these methods may be followed as a basic treatment plan:

  • Patients with renal colic are treated through surgery or by using techniques which basically help the stone pass through the urine.
  • Flank pain in patients with gastrointestinal disorders or appendicitis might require surgery or medications that include antibiotics. Antibiotics are required to treat urinary tract infections.
  • Drugs which alleviate pain are also administered to get rid of the initial symptoms. Anti-inflammatory medications are administered along with physical therapy for patients with spinal arthritis as well as muscle spasms.
  • Apart from rest, medication and treatment based on the underlying disease, patient might need to be hospitalized if it turns severe.







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