Evaluation and Management of Acute Abdominal Pain in Adults

Immediate Assessment and Diagnostic Approach

• The American Academy of Family Physicians recommends beginning with rapid assessment of hemodynamic stability and pain location, obtaining mandatory β-hCG testing in all women of reproductive age, then proceeding directly to CT abdomen/pelvis with IV contrast for nonlocalized pain or ultrasonography for right upper quadrant pain 1, 2, 3
• Patients with hypotension, severe pain out of proportion to exam findings, or signs of peritonitis require immediate surgical consultation rather than extended diagnostic workup 2, 4
• Tachycardia is the most sensitive early warning sign of surgical complications and should trigger urgent investigation even before other symptoms develop 2, 3
• The combination of fever, tachycardia, and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis 2
• Begin rapid intravascular volume resuscitation immediately when hypotension is identified 5

History Taking and Physical Examination

• Location specificity is the most valuable starting point: right upper quadrant suggests hepatobiliary disease, right lower quadrant indicates appendicitis, left lower quadrant points to diverticulitis, and diffuse pain requires broader evaluation 3, 4
• Ripping, tearing, stabbing, or sharp quality pain suggests aortic dissection 2
• Colicky pain indicates bowel obstruction as the bowel attempts to overcome occlusion 2
• Asking about the last bowel movement and passage of gas has 85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction in patients with prior abdominal surgery 2
• Vomiting occurs earlier and more prominently in small bowel obstruction versus large bowel obstruction 2
• The triad of abdominal pain, constipation, and vomiting suggests sigmoid volvulus 2
• Approximately 25% of acute mesenteric ischemia patients have occult blood in stool 2

Laboratory Evaluation and Imaging Strategy

• β-hCG testing is mandatory in all women of reproductive age before proceeding with any imaging to rule out ectopic pregnancy 3, 4
• Complete blood count to assess for leukocytosis indicating infection or inflammation 3, 4
• Comprehensive metabolic panel including liver function tests to evaluate hepatobiliary pathology and organ function 3, 4
• Ultrasonography is the initial imaging test of choice for evaluating acute cholecystitis and hepatobiliary disease 1, 3
• CT of the abdomen and pelvis with contrast is the initial imaging study of choice for suspected appendicitis 1, 3
• CT of the abdomen and pelvis with contrast is recommended, especially for suspected diverticulitis 2
• CT of the abdomen and pelvis with IV contrast is the preferred initial imaging study for nonlocalized or diffuse abdominal pain, as it changes the leading diagnosis in 51% of patients and alters admission decisions in 25% of cases 3

Antimicrobial Therapy and Special Population Considerations

• Antimicrobial therapy should be initiated once intra-abdominal infection is diagnosed or considered likely 5
• For patients with septic shock, antibiotics should be administered as soon as possible 5
• For patients without septic shock, antimicrobial therapy should be started in the emergency department 5
• Satisfactory antimicrobial drug levels should be maintained during a source control intervention 5
• Always consider gynecologic conditions including ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease in women of reproductive age 3, 4
• Elderly patients may have atypical symptoms and require more thorough evaluation, even if laboratory tests are normal 2, 3
• Immunocompromised patients should be considered for intra-abdominal infection if they present with evidence of infection from an undetermined source 5
• Post-bariatric surgery patients often present with atypical symptoms, and tachycardia is the most critical warning sign 2

Critical Pitfalls to Avoid

• Never proceed with CT imaging in reproductive-age women without pregnancy testing, as this leads to delayed diagnosis of ectopic pregnancy and unnecessary fetal radiation exposure 3, 4
• Do not order conventional radiography routinely, as it has limited diagnostic value and rarely changes management 1, 3, 4
• Do not assume normal initial labs exclude serious pathology in patients with high clinical suspicion—proceed to appropriate imaging 4
• Do not delay imaging in clinically deteriorating patients while pursuing additional non-diagnostic tests 4
• Avoid overuse of CT scans to minimize ionizing radiation exposure, especially in young patients 1

Evidence‑Based Diagnostic Findings for Abdominal Pain with Low‑Grade Fever

Epidemiology of Common Surgical Causes

• In adult patients presenting with acute abdominal pain, small‑bowel obstruction accounts for 4–5 % of cases and contributes to roughly 15 % of hospital admissions for acute abdominal pain (World Journal of Emergency Surgery, 2019) 6.
• Colorectal cancer is responsible for about 60 % of large‑bowel obstructions in the emergency setting (World Journal of Emergency Surgery, 2019) 6.

Predictors and Diagnostic Accuracy of Clinical History

• A history of prior abdominal surgery predicts adhesive small‑bowel obstruction with 85 % sensitivity and 78 % specificity (World Journal of Emergency Surgery, 2019) 6.

Imaging Modalities and Their Diagnostic Yield

• Contrast‑enhanced CT doubles the detection rate of cholangitis compared with non‑contrast imaging in a prospective cohort (Journal of the American College of Radiology, 2018) 7.
• CT imaging increases the diagnostic identification of pelvic inflammatory disease by 280 % after imaging is performed (Journal of the American College of Radiology, 2018) 7.
• Rapid MRI protocols identify renal abscesses with 99 % accuracy (Journal of the American College of Radiology, 2018) 7.
• MRI detects ovarian torsion with 86 % sensitivity and 100 % specificity (Journal of the American College of Radiology, 2018) 7.
• CT can reliably guide percutaneous drainage of intra‑abdominal abscesses (including perinephric, diverticular, or other loculated collections) (Journal of the American College of Radiology, 2018) 7.
• CT findings of pseudomembranous (Clostridioides difficile) colitis are present in the colon in 88 % of cases (Journal of the American College of Radiology, 2018) 7.
• Diffuse intra‑abdominal tumors such as lymphomas or metastases may present with abdominal pain and fever; CT is the primary imaging tool for detection (Journal of the American College of Radiology, 2018) 7.

Laboratory and Fluid Analyses

• In patients with cirrhosis and ascites, spontaneous bacterial peritonitis presents with abdominal pain, fever > 100 °F, and tenderness; a diagnostic ascitic fluid polymorphonuclear (PMN) count > 250 cells/mm³ confirms the diagnosis (Hepatology, 2009) 8.
• Secondary bacterial peritonitis from surgically treatable intra‑abdominal sources can mimic spontaneous bacterial peritonitis, emphasizing the need for imaging‑guided evaluation (Hepatology, 2009) 8.
• Among elderly patients with bacteremia, fever ≥100 °F is present in most cases, but 15 % are afebrile; predictors of afebrile bacteremia include shaking chills, hypotensive shock, total band neutrophil count ≥ 1,500 cells/mm³, and lymphocyte count < 1,000 cells/mm³ (Journal of the American Geriatrics Society, 2009) 9.

Clinical Implications

• The high diagnostic yield of contrast‑enhanced CT for cholangitis and pelvic inflammatory disease supports early imaging when these conditions are suspected.
• MRI should be considered first‑line when evaluating suspected renal abscess or ovarian torsion due to its superior accuracy.
• Recognition that a substantial proportion of bacterial peritonitis cases may lack fever in older adults underscores the importance of fluid analysis and imaging rather than reliance on temperature alone.

Imaging and Antibiotic Management in Acute Lower Abdominal Pain with Fever

Primary Imaging Strategy

• For patients presenting with lower abdominal pain, low back pain, and fever, the American College of Radiology recommends contrast‑enhanced CT of the abdomen and pelvis as the first‑line imaging modality. This imaging changes the leading diagnosis in approximately 49–51 % of cases, alters admission decisions in 24–25 %, and modifies surgical planning in about 25 % of patients. 10

Diagnostic Impact of CT

• Contrast‑enhanced CT doubles the detection rate of cholecystitis and cholangitis compared with alternative imaging, and increases identification of pelvic inflammatory disease by 280 %, enabling earlier, condition‑specific treatment. 10
• CT identifies pseudomembranous colitis in 88 % of evaluated cases, supporting its role in diagnosing Clostridioides difficile‑associated colitis in the acute setting. 10

Alternative Imaging for Specific Conditions

• Rapid MRI protocols achieve 99 % accuracy in detecting renal abscesses, providing a radiation‑sparing alternative when CT is contraindicated. 10
• CT guidance enables effective percutaneous drainage of abdominopelvic abscesses, improving source‑control outcomes. 10

Antibiotic Initiation

• The World Journal of Emergency Surgery advises prompt initiation of broad‑spectrum antibiotics once intra‑abdominal infection is suspected or confirmed, regardless of shock status, to reduce morbidity. 11
• In patients with septic shock, antibiotics should be administered as early as possible, ideally within the first hour of recognition, to improve survival. 11
• For patients without septic shock, antimicrobial therapy should be started in the emergency department before definitive source control, ensuring adequate drug levels throughout any subsequent procedures. 11

Source‑Control Timing

• Timely and complete source control is critical; delayed or incomplete interventions are associated with markedly worse outcomes in intra‑abdominal sepsis. 11