Sudden Severe Flank or Side Pain (Renal Colic)
Understanding what may cause sudden severe flank pain, when it may be due to a kidney stone, and when medical assessment is needed.
Overview
Renal colic is the sudden, often severe flank or side pain that commonly occurs when a kidney stone moves into the ureter, the tube that carries urine from the kidney to the bladder.
The pain can be intense and may move from the side or back towards the lower abdomen or groin. Some people also experience nausea, vomiting or blood in the urine.
Although kidney stones are a common cause of renal colic, severe flank pain should be properly assessed. The important questions are whether there is a stone, where it is located, whether it is blocking the kidney, and whether there are signs of infection.
What does renal colic feel like?
Renal colic typically causes sudden, severe pain on one side of the back or abdomen, usually around the area between the ribs and hip.
The pain may:
- start suddenly
- become very intense
- come and go in waves
- move from the back or side towards the lower abdomen or groin
- radiate towards the testicle in men
- make it difficult to sit still or find a comfortable position
Nausea, vomiting and sweating are also common during a severe episode.
Unlike muscular back pain, renal colic is usually not simply related to a particular movement or position.
Why does a kidney stone cause so much pain?
Kidney stones do not always cause pain while they remain inside the kidney.
Pain often begins when a stone moves into the ureter and interferes with the normal drainage of urine from the kidney.
The ureter contracts as it attempts to move the stone towards the bladder. Pressure can also build up above the obstruction.
This combination of ureteric spasm and increased pressure produces the characteristic severe, wave-like pain known as renal colic.
The intensity of the pain does not necessarily tell us how large the stone is. Even a relatively small ureteric stone can cause severe pain.
Where is kidney stone pain usually felt?
The location of pain can sometimes change as a stone moves through the ureter.
| Stone location | Possible pain pattern |
|---|---|
| Kidney or upper ureter | Side, flank or back below the ribs |
| Middle ureter | Side or lower abdomen |
| Lower ureter | Lower abdomen, groin or genital area |
| Near the bladder | Lower abdominal discomfort, urinary urgency or frequent urination |
Pain location alone cannot confirm where a stone is located. Imaging is usually needed to determine the stone’s size, position and degree of obstruction.
Other symptoms that can occur with renal colic
A kidney or ureteric stone may also cause:
- blood in the urine
- nausea or vomiting
- urinary urgency
- passing urine more frequently
- discomfort or burning when passing urine
- cloudy or unpleasant-smelling urine
Some kidney stones cause no symptoms at all and are found incidentally during an ultrasound or CT scan performed for another reason.
When is renal colic an emergency?
Seek urgent medical assessment if severe flank pain occurs with:
- fever or chills
- feeling very unwell, weak or confused
- persistent vomiting or inability to keep fluids down
- difficulty or inability to pass urine
- severe pain that cannot be controlled
- known reduced kidney function
- a solitary functioning kidney
- pregnancy
An obstructed urinary tract with infection is a urological emergency.
In this situation, antibiotics alone may not be sufficient. The obstructed kidney may require urgent drainage with a ureteric stent or, in selected circumstances, a nephrostomy tube before definitive stone treatment.
Is all severe side or back pain caused by kidney stones?
No.
Several conditions can cause pain in a similar area, including:
- muscle or spinal pain
- kidney infection
- gallbladder disease
- appendicitis
- bowel conditions
- gynaecological conditions
- other abdominal or urinary tract problems
For this reason, particularly with a first episode of severe flank pain, it is important not to assume that the symptoms are caused by a kidney stone without appropriate assessment.
How is suspected renal colic assessed?
Assessment usually begins with the pattern of pain, associated symptoms and medical history.
Important information includes:
- where the pain started and where it has moved
- whether the pain comes in waves
- fever or chills
- nausea or vomiting
- blood in the urine
- urinary symptoms
- previous kidney stones
- previous urinary tract infections
- whether there is only one functioning kidney
- previous stone procedures
Depending on the clinical situation, assessment may include physical examination, urine testing, blood tests and imaging.
Urine tests
A urine sample may be checked for:
- blood
- white blood cells
- bacteria or other evidence of infection
Blood in the urine is common with urinary stones, but its absence does not completely exclude a stone.
If infection is suspected, a urine culture may be required.
Blood tests
Blood tests may be performed to assess:
- kidney function
- signs of infection
- blood count
- calcium and other relevant metabolic factors where appropriate
This is particularly important if there is significant obstruction, infection, dehydration or recurrent stone disease.
What scan is used for renal colic?
CT scan
For many adults with suspected acute renal colic or kidney stone pain, a non-contrast CT scan of the kidneys, ureters and bladder (CT KUB) provides detailed information about urinary stones.
It can show:
- whether a stone is present
- the size of the stone
- its exact location
- whether the kidney is obstructed
- whether there is more than one stone
Stone size and location are important because they help determine the likelihood of spontaneous passage and whether treatment may be required.
Ultrasound
Ultrasound can assess the kidneys for stones and signs of urinary obstruction without radiation.
It may be particularly useful in situations where radiation exposure is an important consideration, including pregnancy and younger patients.
The most appropriate imaging test depends on the patient’s age, symptoms and clinical circumstances.
Will a ureteric stone pass by itself?
Yes. Some ureteric stones can pass naturally without an operation, particularly smaller stones. However, the chance of spontaneous passage depends on the stone’s size, location and the patient’s clinical circumstances.
The likelihood of spontaneous passage depends mainly on:
- stone size
- stone location
- degree of obstruction
- severity and persistence of symptoms
- presence or absence of infection
- individual anatomy and clinical circumstances
Smaller stones, particularly those located closer to the bladder, are generally more likely to pass spontaneously.
However, size alone should not determine management.
A small stone may still require treatment if it causes persistent obstruction, repeated severe pain, infection or deterioration in kidney function.
What happens if the stone does not pass?
Treatment depends on the stone’s size and location as well as the patient’s symptoms and overall condition.
Options may include:
Observation
Suitable stones may be monitored while waiting for spontaneous passage, provided pain is manageable and there are no concerning features such as infection or significant kidney impairment.
Follow-up is important to confirm that the stone has passed and that obstruction has resolved.
Medication
Pain relief is an important part of managing acute renal colic.
In selected patients with ureteric stones, medication may also be considered to facilitate stone passage. The suitability of this approach depends on the stone and the individual patient’s condition.
Ureteroscopy and laser stone treatment
A small telescope can be passed through the urinary tract into the ureter or kidney.
The stone can then be fragmented, commonly using laser energy, and the fragments removed where appropriate.
A temporary ureteric stent may sometimes be placed afterwards.
Shock wave lithotripsy
Shock wave lithotripsy uses externally generated shock waves to fragment selected urinary stones into smaller pieces that can subsequently pass through the urinary tract.
Its suitability depends on factors including stone size, location and density.
Learn more about Extracorporeal Shock Wave Lithotripsy (ESWL).
Percutaneous stone surgery
Larger or more complex kidney stones may require percutaneous nephrolithotomy (PCNL) or a smaller-access technique such as mini-PCNL.
The appropriate treatment is determined after reviewing the stone burden, anatomy and individual clinical circumstances.
Does the pain stopping mean the kidney stone has passed?
Not necessarily.
Pain may improve when the stone changes position or when pressure within the urinary tract temporarily decreases.
A stone can occasionally remain in the ureter even after the pain has settled.
If a ureteric stone has been diagnosed and managed conservatively, appropriate follow-up may be recommended to confirm stone passage and ensure that the kidney is no longer obstructed.
Why do some people keep developing kidney stones?
Kidney stones can recur.
Factors that may contribute include:
- inadequate fluid intake
- increased fluid loss in hot environments
- high dietary salt intake
- certain dietary patterns
- family history of kidney stones
- recurrent urinary infections
- metabolic abnormalities
- certain medical conditions or medications
For patients with recurrent stones, further evaluation may include stone analysis, blood tests and 24-hour urine testing to identify factors that may be contributing to stone formation.
This can help guide a more personalised prevention strategy.
Kidney Stones in Malaysia and Other Hot Climates
People living in Malaysia and other tropical climates can lose significant amounts of fluid through sweating.
If this fluid is not adequately replaced, urine becomes more concentrated, which can favour stone formation in susceptible individuals.
Regular fluid intake is therefore an important part of kidney stone prevention, particularly for people who work outdoors, exercise frequently or have previously developed urinary stones.
For people with recurrent kidney stones, fluid intake is generally adjusted to maintain a good urine output throughout the day. The amount required varies with body size, activity and fluid loss, particularly in hot climates.
When should you see a urologist for renal colic?
Urological assessment may be appropriate when:
- a kidney or ureteric stone has been identified
- pain continues or repeatedly returns
- the stone does not appear to be passing
- there is urinary obstruction
- kidney function is affected
- urinary infection occurs with a stone
- stones repeatedly recur
- treatment may be required to relieve obstruction or clear the stone
The decision to observe or treat a stone depends on more than its size alone. Its location, obstruction, symptoms, infection risk and effect on the kidney are also important.
Frequently Asked Questions
Is renal colic the same as kidney stone pain?
Renal colic describes the characteristic severe pain caused by obstruction of the urinary tract, most commonly when a kidney stone enters or becomes lodged in the ureter.
Can a small kidney stone cause severe pain?
Yes. Pain severity does not reliably reflect stone size. A small stone in the ureter can cause very severe pain.
Can kidney stone pain come and go?
Yes. Renal colic commonly occurs in waves as the ureter contracts and pressure within the urinary tract changes.
Can kidney stone pain move from the back to the groin?
Yes. Pain may begin in the flank or back and move towards the lower abdomen, groin or genital area as the stone travels down the ureter.
Can kidney stones cause blood in the urine?
Yes. Kidney and ureteric stones can cause visible or microscopic blood in the urine. However, blood in the urine can have other causes and should be appropriately assessed.
Do I need a CT scan for renal colic?
CT is commonly used to evaluate suspected urinary stones in adults because it can identify the size and location of a stone and whether obstruction is present. Ultrasound may be preferred in certain patients, particularly during pregnancy and in younger people.
Can renal colic cause vomiting?
Yes. Severe renal colic frequently causes nausea and vomiting. Persistent vomiting may lead to dehydration and may require medical treatment.
Is a kidney stone dangerous if there is fever?
A urinary stone associated with obstruction and infection can become serious and requires urgent medical assessment. Fever, chills or feeling significantly unwell with suspected renal colic should not be managed simply by waiting for the stone to pass.
Can the stone still be there after the pain stops?
Yes. Improvement in pain does not always confirm that a ureteric stone has passed. Follow-up imaging may sometimes be needed to ensure that the obstruction has resolved.
When does a kidney stone need surgery?
Intervention may be considered when a stone is unlikely to pass, causes persistent or recurrent pain, produces significant obstruction, affects kidney function or is associated with infection. The most appropriate procedure depends on the stone’s size, location and other clinical factors.
Severe Flank Pain or Suspected Kidney Stone?
Sudden severe pain in the side or back — particularly pain that travels towards the groin, or is accompanied by vomiting or blood in the urine — may be caused by a urinary stone.
Assessment can determine whether a stone is present, whether the kidney is obstructed and whether the stone is likely to pass without intervention.
For severe pain accompanied by fever, chills, inability to pass urine or significant illness, urgent medical assessment is required.