Renal Colic

Epidemiology

Urinary tract calculi represent the single most common cause of acute admission to hospital for a urological cause, making up 1% of all emergency hospital admissions. Population prevalence of calculi is in the region of 0.2% and has a lifetime incidence of 12% in men and 3% in women with a positive family history doubling that risk. First presentation can be without warning at any age; however, generally, its peak incidence follows a bimodal distribution of patients in the early twenties and mid-fifties. An attack of renal colic may be an isolated event in a patients' life or become a recurrent problem, which may have a significant impact on their quality of life with attendant physical and psychosocial morbidity.

History and examination

Suffering renal colic is often considered to be one of the most excruciating experiences a person can go through—it has been described as being the closest a man can come to experiencing the pain of childbirth. Patients tend to describe an acute onset of unilateral pain the site of which can vary loosely depending upon the position of the stone. Renal calculi cause loin pain, whereas ureteric stones can cause a pain radiating towards the groin and those in the lower ureter can cause pain in the testicle or labium.

The pain experienced is typically colicky in nature with a fluctuant course that can last from minutes to hours. Patients classically also suffer nausea and potentially vomiting along with their pain. Patients will be physically restless and unable to settle; this behaviour being in marked contrast to a patient with a peritonitic abdomen who will be suffering a pain exacerbated by movement leaving them reluctant to move at all. It is common to suffer a degree of tenderness on palpation of the loin; however, in simple colic, this will not be exquisite. Certainly, on examination, if features of peritonism, such as rigidity, guarding or rebound tenderness, are present, then another diagnosis is more likely.

Calculi in the lower ureter and bladder may cause irritation precipitating frequency and dysuria and occasionally urinary retention. A mechanical intermittent or complete urinary retention can be caused by stones in the bladder or urethra; however, this is very uncommon as the relative diameter of the lower urinary tract is greater than that of the upper.

Patients very frequently develop microscopic haematuria, which is easily tested for on dipstick. Frank haematuria, while possible, is very uncommon. Dipstick proteinuria in isolation is not associated with urolithiasis. Acute, chronic and recurrent urinary tract infections may also be secondary to calculi (with Proteus species the most prevalent causative organisms). Finally, patients may describe the passage of silt or actual calculi in the urine.

Alternative presentations

One of the most dangerous potential complications of urolithiasis is the development of infection in the urinary tract in the presence of an obstructing calculus. An infected obstructed urinary tract represents a true surgical emergency whereby patients must be admitted immediately to hospital for further investigation and intervention. Suspect this complication if a patient with features typical of renal colic is also demonstrating other signs of systemic sepsis, such as fever and rigours. Urine dipstick positive for leucocytes and nitrites must also attract suspicion. On examination, rather than eliciting a slight tenderness on palpation, the patient may experience a severe tenderness resulting from gross inflammation and destruction of the renal parenchyma.

When assessing any patient with potential renal colic, it is vital to give consideration to any other differential diagnoses in their presentation (see Box 1). The classical misdiagnosis is in not considering a possible ruptured abdominal aortic aneurysm in men over the age of 50 years presenting for the first time with ‘renal colic’. Bilateral loin pain is especially suspicious in this regard.

Aetiology of stones and risk factors for stone formation

Many cases of recurrent renal colic arise as a result of a specific metabolic derangement. Therefore, GPs should have some appreciation of biochemical aetiologies so as to be able to consider further underlying diagnoses and long-term treatment options.

Calcium stones make up 75% of all calculi. Excess urinary excretion of calcium is associated with hyperparathyroidism, sarcoidosis and increased gut absorption of calcium. Patients with high dietary oxalate intake or those who have undergone jejuno ileal bypass or Crohn's disease-related intestinal resections may have increased gut absorption of oxalate and therefore formation of calcium stones. Low levels of citrate and magnesium are also associated with stone formation as they prevent the crystallization of calcium in the urine.

Struvite (magnesium ammonium phosphate) stones, also known as infection stones, make up 15% of cases and are universally associated with urinary tract infection. Organisms include Proteus, Pseudomonas and Klebsiella species; these split urea into ammonium, which subsequently precipitates as a salt. Infections will not resolve until the stone is removed. Urinary pH is typically greater than 7.0.

Six per cent of calculi are composed of uric acid, with increased urinary uric acid resulting from conditions such as gout, malignancy, insulin resistance, renal insufficiency and excess consumption of alcohol. Diets high in purines (meats, legumes and fish) are also implicated. Urinary pH is normally less than 5.5.

Cystine stones are less common making up only 2% of all calculi. Cystinuria is a rare autosomal recessive condition where there is decreased reabsorption of cystine resulting in increased excretion and therefore crystallization.

Stones can also result from the use of numerous different medications. Those most commonly implicated include calcium supplements, vitamin D supplements, acetazolamide, sulphonamides, triamterene and indinavir.

Other general risk factors for recurrent stone formation include a strong family history and first presentation at less than 25 years of age. Patients with any anatomical abnormality of the kidney or urogenital tract are also at more risk. Such abnormalities most often take the form of medullary sponge kidney, horseshoe kidney, pelvi–ureteric junction obstruction, caliceal diverticulum and cysts, ureteral strictures or vesico ureteric reflux.

Patients with a single functioning kidney should also be considered to be at increased risk from stones. This is not because the rate of formation is increased, but because the potential complications are much more immediate and devastating.

Investigation of patients in primary care

All patients with renal colic must, as a minimum, have a number of baseline investigations. Patients should have urine dip performed to confirm the presence of haematuria and rule out urinary tract infection through the presence of nitrites and leucocytes. It should be noted though that various studies have differed in the demonstrable degree of accuracy of this test with a false-negative rate of between 10 and 25% being reported. One should therefore bear in mind that in the presence of a convincing history, a negative result cannot be seen to exclude the possible diagnosis of stones.

Urinalysis should be performed for pH and microscopy of sediment for pathognomic crystals. Patients should also be encouraged to sieve their urine in an attempt to catch any stone that is passed. All patients should have a calculus sent for chemical analysis on at least one occasion. This will allow the accurate determination of the nature of the stone allowing further treatment and secondary prevention measures to be explored.

Acute renal failure resulting from an obstructing unilateral calculus is unlikely given the presence of a normally functioning contralateral kidney. However, checking serum creatinine levels remains a recommendation in all patients and is of course absolutely vital in a patient with a history of chronic renal insufficiency or a single functioning kidney. It should be borne in mind that acute obstruction will only be followed by a rise in creatinine levels after a lag of several hours, raising the possibility of falsely negative tests. Serum urate levels should be tested especially if no stone has yet been obtained. The presence of a radiolucent stone on x-ray and high serum urate levels indicates a uric acid calculus. Serum calcium levels should be tested—a calcium level of greater than 2.6 is suggestive of hyperparathyroidism with further testing of calcium and parathyroid hormone levels indicated.

Management of acute renal colic

The first priority is to control the patients' pain and vomiting. The appropriate route will depend upon severity of pain and whether vomiting has compromised the oral route (Table 1).

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Table 1.

First-line treatment of pain and nausea in the community

Oral analgesia	Parenteral analgesia	Oral antiemetic	Parenteral antiemetic
Oral/rectal diclofenac should be first choice for most patients.	Diclofenac 75 mg intramuscularly. A second dose can be given after 30 minutes as required.	Prochlorperazine—20 mg initially and then 5–10 mg three times daily	Prochlorperazine—12.5 mg by intramuscular injection and reduce the dose by 50% in those with renal insufficiency
Paracetamol and opioids (codeine/tramadol) where non-steroidal anti-inflammatories are contraindicated	Diamorphine—where non-steroidal anti-inflammatories are contraindicated or insufficient	Metoclopramide—10 mg three times daily	Metoclopramide 10mg—avoid if less than 20 years old and reduce the dose by 50% in those with renal insufficiency

A patient with controllable pain who is systemically well and has no other features of complicated renal colic can be safely managed at home. However, if 1 hour following administration of analgesia pain is worsening or intractable, then admission to hospital should be arranged. Other features indicating that a patient must be admitted urgently to secondary care are listed in Box 2. For those managed at home, they must have a supply of simple analgesics and be given advice on when to seek further medical attention if they have further difficulties.

Where the patient does not require emergency admission, further urological advice should still be sought on an urgent outpatient basis. Any patient who is treated expectantly for renal calculi will require periodic follow-up with imaging to ensure that they are progressively passing their stones.

Investigation of renal tract calculi in secondary care

Depending upon the nature of stone disease, further detailed investigation can be carried out through specialist review to definitely diagnose or exclude underlying conditions. This can take the form of 24 hour urine collections and further blood testing.

Plain abdominal x-ray of the kidney, ureter and bladder (KUB) is a simple, cheap and rapid baseline form of imaging (see Fig. 1) that may provide useful differential information. It has sensitivity in the region of 60%, with calcium-containing stones being radio-opaque. Studies are limited by features such as a patients' body habitus, the presence of prominent bowel gas, calculi elsewhere (for example gallstones), constipation or phleboliths (thrombosed veins in the pelvis that can have the appearance of calculi). In situations where the x-ray is positive, further imaging will still be necessary to characterize the anatomy of the calculi and plan further potential intervention.

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Figure 1.

Bilateral staghorn calculi

Unenhanced helical computed tomography KUB (CT KUB) is now the accepted gold standard diagnostic investigation according to the British Association of Urological Surgeons (see Fig. 2). It has been shown to have a specificity and sensitivity in the region of 95%, similar or superior to intravenous pyelography (IVP). CT KUB has the advantage that, along with detecting radiolucent stones, it may also detect pathology outside the renal tract. The main disadvantage of CT scanning is the exposure of the patient to high level irradiation and its impracticality as a tool for follow-up in the long term. The European Association of Urology therefore recognizes combining x-ray KUB and ultrasound KUB as a suitable follow-up tool (although not for initial diagnosis).

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Figure 2.

A CT scan demonstrating a 4 mm calculi in the left mid-ureter (lateral to the superior aspect of the body of the third lumbar vertebrae)

IVP (see Fig. 3), while being accurate, is more limited than CT scanning and will not demonstrate radiolucent stones. Furthermore, IVP carries definite potential risks in terms of possible lactic acidosis in patients treated with metformin and also nephrotoxicity and anaphylaxis to contrast media. For these reasons, IVP will only normally be carried out where CT scanning is unavailable.

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Figure 3.

A normal IVP

Ultrasonography has a limited but useful role in the diagnosis of urolithiasis. While renal stones and hydronephrosis will be demonstrated, stones in the ureter are poorly visualized. In practice, ultrasound is most often used in the emergency setting of a febrile patient to exclude or guide the drainage of a pyonephrosis. It can also be used safely in pregnant women and children where radiation exposure needs to be avoided. Finally, magnetic resonance imaging (MRI) may also be appropriate on occasions such as in pregnancy to avoid irradiation. It does however have very real drawbacks in terms of scanning times and demands on service from other sources.

Treatment of renal tract calculi in secondary care

Once the size of a stone has been measured, it is possible to predict how likely the stone is to be passed spontaneously. Stones less than 5 mm in size have an 80% chance of spontaneous passage, whereas those greater than 7 mm have a very low chance of being passed.

Special circumstances

Secondary prevention of stone recurrence

Any patient who has had a single episode of renal colic is at increased risk of recurrence in the future; therefore, education on potential dietary changes is essential in the long term. All patients should be advised to stay well hydrated as it has been shown that there is an inverse relationship between fluid intake and stone formation. It has been suggested that aiming for a urine output of at least 2 l/day is an effective target for patients.

All patients should have a balanced varied diet; a diet high in vegetables being particularly desirable as it tends to alkalinize the urine. Unfortunately, some fruits and vegetables are high in oxalate and should only be consumed in a limited fashion—these foods include rhubarb, spinach, cocoa, tea leaves and nuts.

Excessive consumption of meat may lead to undesirable metabolic changes and acidification of urine and it is therefore recommended that patients avoid eating more than 1 g/kg bodyweight of protein. Sodium intake should also be controlled as it will lead to increased levels of calcium in the urine and also formation of sodium urate crystals. Borghi et al. have demonstrated that a diet low in sodium and animal proteins will lead to 50% reduction in stone formation in patients with calcium stones.

Due to calcium's role in binding oxalate and preventing its precipitation, patients should not be encouraged to restrict intake of calcium. However, only those with confirmed hyperoxaluria should be started on calcium supplements as excessive intake will lead to calcium stone formation. In patients with confirmed uric acid stone disease, the intake of uric acid should not exceed 500 mg/day. Foods rich in urate include liver, kidneys, poultry skin, herring, sardines and anchovies.

Pharmacological treatments

Any pharmacological treatment should only be considered after a patient has received good advice on fluid intake and potential dietary changes as it is these changes that are more likely to be of benefit to patients rather than any form of medication. Continued compliance with dietary and drinking recommendations must also always be encouraged.

Thiazide diuretics (such a bendroflumethiazide and hydrochlorothiazide) can be commenced in those with hypercalciuria as they have been shown to decrease urinary levels of calcium; however, their efficacy has not been proven in other settings.