Assessing renal colicRenal colic is generally caused by stones in the upper urinary tract (urolithiasis) obstructing the flow of urine; a more clinically accurate term for the condition is therefore ureteric colic.2 The blockage in the ureter causes an increase in tension in the urinary tract wall, stimulating the synthesis of prostaglandins, causing vasodilatation. This leads to a diuresis which further increases pressure within the kidney. Prostaglandins also cause smooth muscle spasm of the ureter resulting in the waves of pain (colic) felt by the patient. Occasionally renal colic will occur due to a cause other than urinary stones, such as blood clots that may develop with upper urinary tract bleeding, sloughed renal papilla (e.g. due to sickle cell disease, diabetes, long-term use of analgesics) or lymphadenopathy.3 Show
Individual urinary stones are aggregations of crystals in a non-crystalline protein matrix.3 Eighty percent of urinary stones are reported to contain calcium, frequently in the form of calcium oxalate.3 Calcium phosphate and urate are also found in urinary stones in decreasing frequency, although urate may be more prevalent in patients who are obese.3 Bacteria can also cause the formation of calculi, referred to as infection stones, which contain magnesium ammonium phosphate and may be large and branched; these are also known as staghorn calculi.3 The pain of renal colic develops suddenly and is often described by patients as “the worst pain they have ever felt”.4 Despite this severe presentation, the majority of urinary stones pass spontaneously.4 Therefore many patients with renal colic can be managed in primary care with a watchful waiting approach if there are no red flags present, their pain can be controlled and a prompt referral for imaging is arranged.3 Which patients are most likely to develop urinary stones?It is estimated that 12% of males and 6% of females will experience an episode of renal colic at some stage in their life, with incidence peaking between age 40 and 60 years for males, and in the late 20’s for females.3 Urinary stones are more likely to occur in patients who have:3
Between 30 – 40% of people will experience reccurrent renal colic within five years of their first episode.3 Diagnosing renal colicPatients with renal colic classically present with sudden and severe loin pain that occurs in waves of intensity and may be accompanied by nausea and vomiting. Some patients may be symptom-free between these episodes. This description helps to distinguish renal colic from some other conditions causing abdominal pain (see differential diagnosis below). The site of the pain is generally not useful for predicting the location of the stone within the renal tract, however, new onset lower urinary tract symptoms are consistent with a stone migrating distally.2 If the stone is located at the vesico-ureteric junction patients may experience straining when urinating, with painful and frequent passage of small volumes of urine (strangury), due to the stone irritating the detrusor muscle.3 Examining the patientPatients with renal colic typically appear restless and unable to find a comfortable position. Classical renal colic pain is located in the costovertebral angle, lateral to the sacrospinus muscle and beneath the 12th rib.3 The pain may radiate to the flank, groin, testes or labia majora.3 Acute kidney injury is a concern in patients with renal colic. It is important to be aware of a previous nephrectomy or any other cause of renal impairment which would increase the significance of further renal injury and lower the threshold for referral to the emergency department (see “Red Flags”). Assess for signs and symptoms of infection. Another concern in patients with renal colic is the development of pyonephrosis (infection of the renal system above an obstructing stone). If this occurs then the patient can develop life-threatening sepsis. Diagnostic uncertainty is an indication for referral to hospital as renal colic can be difficult to differentiate from a number of other conditions, including:3, 5
Investigating suspected renal colicThe following investigations should be performed or requested to detect haematuria, rule-out infection, assess kidney function and assess for the presence of an underlying metabolic condition, such as gout, hyperparathyroidism or renal tubular acidosis: 2, 3, 5
Approximately 90% of patients with urinary stones will return a positive test for haematuria on urine dipstick, therefore a negative result is a reason to reconsider the diagnosis.3 A midstream urine sample should be sent for microscopy to assess for the presence of dysmorphic red blood cells and urinary casts to exclude other causes such as glomerular injury.2 Patients with reduced kidney function, e.g. creatinine > 160 mmol/L, who are at immediate risk of acute kidney injury (AKI) should be referred to the emergency department. N.B. the patient’s white blood cell count may be elevated in the absence of infection.2 Serum urate levels may also fluctuate due to acute inflammation.3
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