How should I evaluate and manage a patient presenting with lower abdominal pain, low back pain, and fever?

Evaluation and Management of Lower Abdominal Pain, Low Back Pain, and Fever

Obtain a pregnancy test immediately if the patient is female and of reproductive age, then proceed directly to CT abdomen/pelvis with IV contrast as your primary diagnostic tool, while simultaneously initiating hemodynamic assessment and broad-spectrum antibiotics if sepsis is suspected. 1

Immediate Priorities

Assess hemodynamic stability first – check for hypotension, tachycardia (the most sensitive early warning sign of surgical complications), tachypnea, and signs of peritonitis, as this triad predicts serious complications including perforation or sepsis. 1 If hypotension is present, begin rapid intravascular volume resuscitation immediately. 1 Patients with severe pain out of proportion to exam findings or peritoneal signs require immediate surgical consultation rather than extended workup. 1

Mandatory Initial Testing

For Women of Reproductive Age

• β-hCG testing (urine or serum) is absolutely mandatory before any imaging, regardless of reported sexual history or contraceptive use. 1, 2 Never assume a patient is not pregnant based on history alone. 2 This fundamentally changes your diagnostic approach and imaging safety. 2
• If β-hCG is positive, proceed with transvaginal and transabdominal ultrasound rather than CT. 2

For All Patients

• Complete blood count to assess leukocytosis indicating infection or inflammation 1
• Comprehensive metabolic panel including liver function tests 1
• Consider sexually transmitted infection testing (nucleic acid amplification tests for Chlamydia and Neisseria gonorrhoeae) if the patient is sexually active, as pelvic inflammatory disease detection increases by 280% with CT imaging 3, 2

Primary Imaging Strategy

CT abdomen and pelvis with IV contrast is your first-line imaging study for this presentation. 3, 1 This is the gold standard because it:

• Changes the leading diagnosis in 49-51% of cases 3, 1
• Alters admission decisions in 24-25% of cases 3, 1
• Modifies surgical plans in 25% of cases 3
• Increases detection of cholecystitis/cholangitis by 100% 3
• Increases detection of pelvic inflammatory disease by 280% 3
• Detects pseudomembranous colitis in 88% of cases 3

Do not order conventional radiography – it has limited diagnostic value and rarely changes management. 1, 4

Critical Differential Diagnoses to Consider

The combination of lower abdominal pain, low back pain, and fever strongly suggests retroperitoneal pathology or complicated intra-abdominal infection:

Most Likely Diagnoses

• Perforated diverticulitis with retroperitoneal extension – this can present with lower abdominal pain radiating to the back and fever, particularly in the sigmoid colon 5, 6
• Complicated appendicitis with abscess – may have atypical presentations with back pain from retroperitoneal extension 1, 7
• Psoas abscess (from Crohn's disease or other sources) – classically presents with fever, lower abdominal pain, and back/hip pain 7
• Pyelonephritis or renal abscess – rapid MRI protocols identify renal abscesses with 99% accuracy 3
• Pelvic inflammatory disease (in women) – CT increases diagnostic identification by 280% 3

Less Common but Critical

• Spontaneous bacterial peritonitis (if cirrhosis/ascites present) – diagnosed by ascitic fluid PMN count >250 cells/mm³ 1
• Retroperitoneal lymphangiomyoma infection (rare, primarily in women of childbearing age) 8

Antibiotic Therapy

Initiate broad-spectrum antibiotics once intra-abdominal infection is diagnosed or considered likely. 3, 1 For patients with septic shock, administer antibiotics as soon as possible. 3, 1 For patients without septic shock, start antimicrobial therapy in the emergency department. 3, 1 Maintain satisfactory drug levels during any source control intervention. 3

Source Control Considerations

Timing and adequacy of source control are critical – late or incomplete procedures have severely adverse outcomes. 3 CT can guide percutaneous drainage of abdominopelvic abscesses effectively. 3 For perforated appendicitis with abscess, small abscesses (<3-4 cm) can be treated with antibiotics alone for 7 days, while large abscesses require percutaneous drainage combined with antibiotics. 7

Pain Management

Provide immediate pain relief without withholding medication while awaiting diagnosis – pain control facilitates better physical examination without affecting diagnostic accuracy. 7, 4 Use oral NSAIDs for mild-to-moderate pain if no contraindications exist, and intravenous opioid analgesics titrated to effect for severe pain. 7

Critical Pitfalls to Avoid

• Never proceed with CT in reproductive-age women without pregnancy testing – this leads to delayed diagnosis of ectopic pregnancy and unnecessary fetal radiation exposure. 1, 2
• Do not assume normal initial labs exclude serious pathology – proceed to appropriate imaging if clinical suspicion is high. 1
• Do not delay imaging in clinically deteriorating patients while pursuing additional non-diagnostic tests. 1
• Recognize that 15% of elderly patients with bacteremia are afebrile – do not rely on fever alone to rule out infection. 1
• In post-bariatric surgery patients, tachycardia is the most critical warning sign even with atypical symptoms. 1

Disposition and Follow-Up

Instruct the patient to return immediately if severe or progressive pain develops, fever persists beyond 48-72 hours of treatment, or new neurological symptoms appear. 7 Monitor for persistent fever, leukocytosis, or failure of symptoms to improve, as these indicate high risk of ongoing intra-abdominal infection requiring additional intervention. 7