Investigations

These may be classified into:

• early - investigations to be performed on admission
  • urine dipstix for microscopic haematuria:
    • may be negative in pelvi-ureteric junction obstruction (1)
    • urine microscopy, culture and sensitivity - testing the urine for blood, pus cells and evidence of infection
    • assessment of renal function - serum urea, creatinine, electrolytes (1,2)
      
      
  • NICE suggest (3):
    • urgent (within 24 hours of presentation) low-dose non-contrast CT to adults with suspected renal colic. If a woman is pregnant, offer ultrasound instead of CT
    • non-contrast computed tomography of the kidneys, ureters, and bladder (CT KUB) is the firstline investigation (sensitivity ~95%, specificity ~98%) (4)
      • however, ultrasound is indicated for children and pregnant women (sensitivity ~84%, specificity ~53%)
    • urgent (within 24 hours of presentation) ultrasound as first-line imaging for children and young people with suspected renal colic
    • if there is still uncertainty about the diagnosis of renal colic after ultrasound for children and young people, consider low-dose non-contrast CT
      
      
  • abdominal radiology:
    • 90% of stones are radio-opaque
    • only urate and xanthine stones are translucent
    • it is important to request imaging of the kidney, ureter and bladder so as not to miss stones in the lower ureter or the vesicoureteric junction
  • intravenous urogram - now rarely used:
    • will confirm the diagnosis and show the position of obstruction
    • is best performed acutely
    • abdominal ultrasound is an alternative
    • contraindicated if there is a clear history of allergy to contrast material
  • noncontrast Helical (spiral) CT
    • used increasingly in the initial assessment of renal colic
    • fast and accurate, and it readily identifies all stone types in all locations
      • sensitivity (95 to 100 percent) and specificity (94 to 96 percent) suggest that it may definitively exclude stones in patients with abdominal pain
    • associated features of renal colic such ass renal enlargement, perinephric or periureteral inflammation or "stranding," and distension of the collecting system or ureter, are sensitive indicators of the degree of ureteral obstruction
    • density of calculi may be used to distinguish cystine and uric acid stones from calcium-bearing stones and is capable of further subtyping the calcium stones into calcium phosphate, calcium oxalate monohydrate and calcium oxalate dihydrate stones
    • also useful in diagnosing nonurologic causes of abdominal pain, such as abdominal aortic aneurysms and cholelithiasis
    • its emergence as the definitive initial imaging modality for urolithiasis allows intravenous pyelography to be mainly reserved for therapeutic planning in complex stone cases
      
      
• late - investigations to be performed as the acute episode is resolving
  • investigations to be performed once the initial diagnosis of a urinary calculus has been made include (1,2):
  • tests for metabolic disorder:
    • serum calcium, phosphate, uric acid, alkaline phosphatase
    • random urine 'spot' test for cystine
    • random urine for pH:
      • pH greater than 7.5 - infective stones
      • pH below 5.5 - urate stones
    • 24-hour urinary collections for calcium, phosphate and and uric acid excretion, and creatinine clearance; ideally, at home, on a normal diet with clear instructions given to the patient
    • renography - to assess the degree of renal outflow obstruction; necessary if conservative treatment planned
    • biochemical analysis of recovered stones
  • NICE state with respect to metabollic testing (3):
    • metabolic testing
      • consider stone analysis for adults with ureteric or renal stones
      • measure serum calcium for adults with ureteric or renal stones
      • consider referring children and young people with ureteric or renal stones to a paediatric nephrologist or paediatric urologist with expertise in this area for assessment and metabolic investigations

Reference:

• 1. Portis AJ, Sundaram , CP.Diagnosis and Initial Management of Kidney Stones. American Family Physician 2001.
• 2. Mostafavi MR et al. Accurate determination of chemical composition of urinary calculi by spiral computerized tomography. J Urol 1998;159:673-5
• 3. NICE (December 2018).Renal and ureteric stones: assessment and management (NG118)
• 4. Wilcox CR et al. Kidney stone disease: an update on its management in primary care. BJGP 2020; 70: 205–206.