Diagnostic Approach for Lower Back Pain and Left Abdominal Pain

Initial Assessment and Laboratory Tests

The American College of Radiology recommends considering both musculoskeletal and visceral causes for the combined presentation of lower back pain and left abdominal pain 1, 2
The combination of symptoms suggests possible diverticulitis, kidney stone, or other intra-abdominal pathology, with the American Academy of Family Physicians noting the importance of early diagnosis 3, 1
A Complete Blood Count (CBC) can help evaluate for infection or inflammation, with leukocytosis suggesting diverticulitis, appendicitis, or other inflammatory processes 3
Urinalysis can help evaluate for urinary tract infection or kidney stones, with hematuria indicating urolithiasis and pyuria suggesting urinary tract infection 4
Elevated C-reactive protein (CRP) and/or Erythrocyte Sedimentation Rate (ESR) can help identify infection or inflammation, with an ESR ≥20 mm/h having 78% sensitivity and 67% specificity for cancer when evaluating back pain 1, 5

The American College of Radiology recommends a CT scan of the abdomen and pelvis with contrast as the most appropriate initial diagnostic test for left lower quadrant pain, with a rating of 8 (usually appropriate) 3, 1, 4
CT abdomen and pelvis with contrast is highly accurate for detecting diverticulitis and can identify other causes including kidney stones, abscesses, and bowel pathology 3
Plain radiography is not recommended as an initial test for nonspecific back pain or left lower quadrant pain due to low sensitivity and unnecessary radiation exposure 5, 1, 6, 7

The American College of Radiology suggests considering MRI if there are concerning features such as severe or progressive neurologic deficits, suspected cauda equina syndrome, history of cancer, or suspected vertebral infection 5, 7, 8
The American Academy of Family Physicians notes that diverticulitis classic triad (left lower quadrant pain, fever, leukocytosis) is present in only 25% of patients, making imaging crucial 1, 4
Avoid routine imaging for uncomplicated acute back pain without red flags, as recommended by the American College of Radiology and the Annals of Internal Medicine 5, 8