What is the initial workup for a patient presenting with flank pain in the Emergency Department (ED)?

Initial Workup for Flank Pain in the Emergency Department

The initial workup for a patient presenting with flank pain in the Emergency Department should include urinalysis, complete blood count, basic metabolic panel, and non-contrast CT of the abdomen and pelvis as the imaging study of choice to evaluate for urolithiasis and other potential causes.

Diagnostic Approach

History and Physical Examination Elements

When evaluating flank pain, focus on these specific elements:

• Pain characteristics:

  • Location and radiation (flank to groin suggests urolithiasis)
  • Onset (sudden vs gradual)
  • Severity (renal colic is often described as excruciating)
  • Aggravating/alleviating factors

• Associated symptoms:

  • Nausea/vomiting (common with renal colic)
  • Hematuria (visible or microscopic)
  • Fever/chills (suggests infection)
  • Urinary symptoms (frequency, urgency, dysuria)

• Past medical history:

  • Previous kidney stones
  • Urinary tract infections
  • Kidney disease
  • Malignancy

• Physical examination focus:

  • Vital signs (fever suggests infection)
  • Costovertebral angle tenderness (positive with pyelonephritis or renal colic)
  • Abdominal examination for other causes of pain
  • Testicular examination in males (to rule out referred pain)

Laboratory Studies

Order these tests immediately:

1. Urinalysis - Essential first test to detect:

   • Hematuria (suggests stone disease or malignancy)
   • Pyuria/nitrites/leukocyte esterase (suggests infection)
   • Proteinuria
   • pH (helps determine stone composition)

2. Complete Blood Count (CBC)

   • Elevated WBC suggests infection
   • Anemia may indicate malignancy or bleeding

3. Basic Metabolic Panel

   • Assess kidney function (BUN, creatinine)
   • Electrolyte abnormalities
   • Calcium levels (hypercalcemia associated with certain stones)

Imaging Studies

1. Non-contrast CT Abdomen and Pelvis

   • Gold standard for diagnosing urolithiasis with 97% sensitivity 1
   • Can identify stone size, location, and degree of obstruction
   • Detects alternative diagnoses causing flank pain
   • Should be performed on all patients with first episode of acute flank pain 2

2. Ultrasound

   • Alternative when CT is contraindicated (pregnancy, radiation concerns)
   • Up to 100% sensitive and 90% specific for ureteral obstruction 1
   • Less sensitive than CT for detecting actual stones
   • Can detect hydronephrosis, perinephric fluid
   • Addition of color Doppler improves sensitivity for small renal stones 1

3. Plain Radiography (KUB)

   • Limited role as standalone test
   • Can be combined with ultrasound to improve detection
   • Less sensitive than CT for stone detection

Common Diagnostic Pitfalls

1. Assuming all flank pain with hematuria is kidney stones

   • Consider alternative diagnoses like renal cell carcinoma 3, pyelonephritis, or Page kidney 4
   • Up to 37% of patients have their diagnosis changed after testing 5

2. Missing serious alternative diagnoses

   • Abdominal aortic aneurysm
   • Renal infarction
   • Appendicitis (especially retrocecal)
   • Diverticulitis
   • Bowel obstruction 1

3. Inadequate pain management while awaiting diagnosis

   • Pain control should be initiated promptly with NSAIDs or opioids 2

4. Overlooking signs of infection requiring urgent intervention

   • Obstructing stone with infection is a urologic emergency
   • Check for fever, elevated WBC, pyuria

Management Decision Algorithm

1. Immediate intervention needed if:

   • Signs of infection with obstruction (obstructive pyelonephritis)
   • Acute kidney injury with complete obstruction
   • Intractable pain or vomiting
   • Solitary kidney with obstruction

2. Outpatient management appropriate if:

   • Small stone (<5mm) with minimal/no obstruction
   • Adequate pain control achieved
   • No signs of infection
   • Normal renal function
   • Reliable follow-up

3. Admission criteria:

   • Stones >5mm (less likely to pass spontaneously)
   • Inadequate pain control
   • Inability to tolerate oral intake
   • Signs of infection
   • Impaired renal function

Conclusion

The initial ED workup for flank pain should be comprehensive but focused on ruling out serious pathology while establishing the most likely diagnosis. Non-contrast CT remains the imaging modality of choice for most patients, with consideration of ultrasound in specific populations like pregnant patients. Laboratory studies should include urinalysis, CBC, and basic metabolic panel to guide further management decisions.