What is the initial workup for a patient with suspected kidney stones in a primary care setting?

Initial Workup for Suspected Kidney Stones in Primary Care

The initial workup for suspected kidney stones in primary care should include ultrasound as the primary diagnostic tool, along with basic laboratory tests including urinalysis, serum electrolytes, calcium, creatinine, and uric acid. 1, 2

Diagnostic Imaging

• Ultrasound is the recommended first-line imaging modality with 45% sensitivity and 94% specificity for ureteral stones and 88% specificity for renal stones 1
• If ultrasound is inconclusive or additional information is needed, non-contrast CT scan should be performed as the standard second-line imaging for acute flank pain 1, 2
• Low-dose CT maintains high diagnostic accuracy (93.1% sensitivity, 96.6% specificity) while reducing radiation exposure 1
• Plain kidney-ureter-bladder (KUB) radiography can help differentiate between radioopaque and radiolucent stone types and is useful for follow-up 1

Laboratory Evaluation

• Urinalysis with both dipstick and microscopic evaluation to assess:
  • Urine pH (helps identify stone type)
  • Presence of blood (hematuria)
  • Signs of infection
  • Crystal identification that may indicate stone type 3, 2
• Basic serum chemistry panel including:
  • Electrolytes
  • Calcium
  • Creatinine
  • Uric acid
  • Blood cell count
  • C-reactive protein (if infection is suspected) 1, 3, 2
• Urine culture if urinalysis suggests infection or if patient has history of recurrent UTIs 3, 2

Pain Management

• NSAIDs are the first-line treatment for renal colic, preferably diclofenac 75 mg intramuscularly 1, 4
• NSAIDs are more effective than antispasmodics and reduce the need for additional analgesia compared to opioids 1, 4
• Opioids should be considered as second-choice analgesics when NSAIDs are contraindicated 1
• Pain control should be maintained for at least six hours 1

Criteria for Immediate Referral/Admission

• Patients with:
  • Fever or signs of infection
  • Intractable pain not responding to analgesia within one hour
  • Solitary kidney
  • Bilateral obstruction
  • Acute kidney injury 1

Metabolic Evaluation

• For first-time stone formers with low risk of recurrence, limited evaluation is sufficient 3
• More comprehensive metabolic evaluation with 24-hour urine collection is recommended for:
  • High-risk first-time stone formers (family history, one kidney, intestinal disease)
  • All recurrent stone formers
  • Patients with bilateral or multiple stones 3, 2
• The 24-hour urine collection should analyze at minimum:
  • Total urine volume
  • Urine pH
  • Calcium
  • Oxalate
  • Uric acid
  • Citrate
  • Sodium
  • Potassium
  • Creatinine 3, 2

Stone Analysis

• Stone analysis should be performed for all first-time stone formers when stone material is available 1, 3
• Patients should be instructed to strain their urine to catch any passed stones for analysis 1
• Repeat stone analysis is justified in patients not responding to treatment, as stone composition may change over time 1, 3

Special Considerations

• For pregnant women, ultrasound is strongly recommended as first-line imaging, followed by MRI as second-line, and low-dose CT only as a last resort 1
• For children with suspected stones, ultrasound is also the first-line imaging modality 1
• Genetic testing should be considered for patients with early-onset stone disease (≤25 years), suspected inherited disorders, recurrent stones, bilateral disease, or strong family history 1

Follow-up

• Patients managed at home should be instructed to:
  • Drink plenty of fluids
  • Strain urine to catch any passed stones
  • Contact the doctor if pain worsens or new symptoms develop 1
• A follow-up phone call should be made one hour after initial assessment and analgesia administration 1
• Fast-track investigation should be arranged for patients meeting criteria for home management 1