According to the text "Clinical Methods," flank pain is a "sensation of discomfort, distress, or agony in the part of the body below the rib and above the ilium." In short, pain on the sides or small of the back is flank pain. Patients who experience such pain for more than a few hours should contact a doctor because it can be symptomatic of kidney disease.
Quality of Pain
The quality of flank pain is an important clue as to the underlying disorder. Some patients present with flank pain on one side and not the other while others have it centralized in their lower back. Some patients have sharp and stabbing pain while others have a persistent dull ache. In some instances, the pain may radiate toward the testis or the abdomen. Sometimes the pain is associated with other symptoms such as nausea, fatigue, blood in the urine,
Sharp stabbing pain suggests that there is some kind of obstruction in the ureters. The ureters are the passageway between the kidneys and the bladder. While kidney stones are the most common cause of the obstructions, blood clots in the ureters can cause similar pain. In some instances, this pain radiates to the scrotal skin or the labia. Often this pain comes in waves lasting 20 to 60 minutes. Fortunately, the pain goes away completely once the stone is passed. This pain is so excruciating that drug addicts often claim to have kidney stones as a way to obtain drugs.
A persistent dull ache accompanied by a low-grade fever correlates with urinary infections. This pain may be accompanied by fever and fatigue. Other causes of dull pain include inflammatory disorders associated with various chronic diseases such as IgA nephropathy, membranoproliferative glomerular nephritis (MPGN), FSGS, and others.
Cancer can be a cause of flank pain. Generally, however, this does not occur unless the tumor is relatively large.
Since the primary way to treat flank pain is to treat the underlying disorder, a good diagnostic workup is important. Doctors routinely obtain urine specimens to perform urinalysis on patients presenting with these symptoms. Other tests such as ultrasound, abdominal CT scan, cytoscopy, intravenous pyelography and others may also be performed. Information gained in these tests is important for diagnosis and treatment.
Patients should not assume that the cause of their pain is related to their kidneys. The Merck Manual states that "ruptured and occasionally unruptured abdominal aortic aneurysms, problems with the spine or spinal nerves, musculoskeletal injuries, and tumors that involve the back of the abdomen" can also cause flank pain.