What labs to order for a patient with lower back pain and left abdominal pain for one week?

Laboratory Tests for Patient with Lower Back Pain and Left Abdominal Pain

For a patient presenting with lower back pain and left abdominal pain for one week, a CT scan of the abdomen and pelvis with contrast is the most appropriate initial diagnostic test.

Diagnostic Approach

Initial Assessment

• Consider both musculoskeletal and visceral causes for the combined presentation of lower back pain and left abdominal pain 1
• The combination of symptoms suggests possible diverticulitis, kidney stone, or other intra-abdominal pathology 1

Laboratory Tests to Order

• Complete Blood Count (CBC) to evaluate for infection or inflammation 2, 3

  • Leukocytosis may suggest diverticulitis, appendicitis, or other inflammatory processes
  • Anemia may indicate gastrointestinal bleeding

• Basic Metabolic Panel (BMP) 2, 3

  • Electrolyte abnormalities may indicate dehydration or metabolic derangements
  • Elevated creatinine may suggest renal involvement or urinary tract obstruction

• Urinalysis to evaluate for urinary tract infection or kidney stones 2, 3

  • Hematuria may indicate urolithiasis
  • Pyuria suggests urinary tract infection

• C-reactive protein (CRP) and/or Erythrocyte Sedimentation Rate (ESR) 1, 3

  • Elevated inflammatory markers may help identify infection or inflammation
  • ESR ≥20 mm/h has 78% sensitivity and 67% specificity for cancer when evaluating back pain 1

• Liver function tests if right upper quadrant involvement is suspected 2, 3

• Lipase to rule out pancreatitis 2, 3

Imaging Recommendations

• CT abdomen and pelvis with contrast is the preferred initial imaging study 1

  • Most useful examination for left lower quadrant pain
  • Highly accurate for detecting diverticulitis, which is common in left-sided abdominal pain
  • Can identify other causes including kidney stones, abscesses, and bowel pathology
  • The American College of Radiology gives CT with contrast a rating of 8 (usually appropriate) for left lower quadrant pain 1

• Plain radiography is not recommended as an initial test for nonspecific back pain or left lower quadrant pain 1

  • Low sensitivity for detecting sources of abdominal pain
  • Unnecessary radiation exposure without significant diagnostic benefit

Special Considerations

When Back Pain May Require Further Evaluation

• Consider MRI if there are concerning features such as: 1
  • Severe or progressive neurologic deficits
  • Suspected cauda equina syndrome
  • History of cancer
  • Suspected vertebral infection
  • Symptoms persisting beyond 4-6 weeks despite conservative treatment

Potential Pitfalls

• Don't assume back pain is always musculoskeletal in origin; visceral causes like duodenal ulcers can refer pain to the back 4
• Diverticulitis classic triad (left lower quadrant pain, fever, leukocytosis) is present in only 25% of patients, making imaging crucial 1
• Avoid routine imaging for uncomplicated acute back pain without red flags 1
• Be aware that in elderly patients, laboratory tests may be normal despite serious infection 1

Follow-up Testing

• If initial laboratory tests are inconclusive but symptoms persist, proceed with CT imaging 1
• For female patients of reproductive age, consider transvaginal ultrasound if gynecologic pathology is suspected 1
• If kidney stones are suspected based on urinalysis, non-contrast CT has nearly 100% sensitivity and specificity 1