What is the appropriate initial evaluation and management for a 19‑year‑old woman presenting with abdominal pain?

Initial Evaluation of Abdominal Pain in a 19-Year-Old Woman

Obtain a serum or urine β-hCG immediately, followed by transvaginal and transabdominal ultrasound as first-line imaging if pregnancy-related pathology is suspected, or proceed directly to CT abdomen/pelvis with IV contrast if β-hCG is negative and pain is non-localized or suggests non-gynecologic pathology. 1, 2, 3

Immediate Assessment and Red Flags

• Check vital signs immediately to identify fever (infection/abscess), tachycardia (bleeding, sepsis, or surgical complication), hypotension (hemorrhage or septic shock), or tachypnea (sepsis or respiratory cause). 2, 4
• Assess for peritoneal signs including rigid abdomen, rebound tenderness, or guarding, which indicate perforation, ischemia, or advanced infection requiring urgent surgical consultation. 2, 4
• Evaluate for pain out of proportion to physical findings, which strongly suggests mesenteric ischemia and requires immediate CT angiography. 2, 4
• Document abdominal distension with vomiting, which indicates bowel obstruction. 2, 4

Mandatory First Laboratory Test

β-hCG testing is non-negotiable in all women of reproductive age before any imaging or definitive management. 1, 2, 4, 3

• Failure to obtain β-hCG can result in missed ectopic pregnancy (which has a positive likelihood ratio of 111 when an adnexal mass is present without intrauterine pregnancy), inappropriate radiation exposure, and potential maternal mortality. 5, 1
• A positive β-hCG immediately narrows the differential to pregnancy-related complications (ectopic pregnancy, threatened abortion, corpus luteum hemorrhage) versus incidental pregnancy with non-obstetric pathology. 1
• A negative β-hCG effectively excludes pregnancy complications and allows radiation-based imaging without concern. 1

Additional Laboratory Tests

• Complete blood count to assess for leukocytosis (infection, appendicitis, pelvic inflammatory disease) or anemia (hemorrhage). 4, 3
• C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease. 4
• Metabolic panel, liver function tests, lipase if epigastric pain or right upper quadrant pain suggests hepatobiliary or pancreatic pathology. 4, 3
• Urinalysis to evaluate for urinary tract infection or urolithiasis. 3
• Lactate if mesenteric ischemia is suspected, though normal lactate does not exclude early ischemia. 4

Imaging Strategy Based on β-hCG Result

If β-hCG is Positive

Perform transvaginal AND transabdominal ultrasound immediately. 5, 1, 3

• Ultrasound has 93% sensitivity and 98% specificity for tubo-ovarian abscess, and identifies ectopic pregnancy with high accuracy when an adnexal mass is visualized without intrauterine pregnancy. 5, 1
• Key ultrasound findings:
  • Intrauterine gestational sac with yolk sac or fetal pole confirms intrauterine pregnancy. 5
  • Endometrial thickness <8mm virtually excludes normal intrauterine pregnancy; ≥25mm virtually excludes ectopic pregnancy. 1
  • Extrauterine gestational sac with yolk sac or fetal pole confirms ectopic pregnancy. 5
  • Adnexal mass without intrauterine pregnancy has positive likelihood ratio of 111 for ectopic pregnancy. 1
  • Thick-walled (>5mm) complex adnexal mass with "cogwheel" sign suggests tubo-ovarian abscess. 1
• Do not use CT as first-line when β-hCG is positive due to radiation exposure; CT may only incidentally reveal ectopic-related findings. 1
• If ultrasound is indeterminate and β-hCG >2,000 mIU/mL without intrauterine pregnancy, ectopic pregnancy risk is 57%. 5

If β-hCG is Negative

Proceed with imaging based on pain location and clinical suspicion. 1, 2, 3

For Right Lower Quadrant Pain:

• CT abdomen and pelvis with IV contrast is first-line, with 95% sensitivity and 94% specificity for appendicitis, and identifies alternative diagnoses in 94% of cases. 2, 4, 3
• Ultrasound may be considered first to minimize radiation, but CT should follow if ultrasound is non-diagnostic. 4, 3
• Differential includes appendicitis, ovarian cyst (hemorrhagic or ruptured), ovarian torsion, nephrolithiasis, inflammatory bowel disease, or pelvic inflammatory disease. 2, 6

For Right Upper Quadrant Pain:

• Ultrasound is first-line to evaluate for acute cholecystitis, cholelithiasis, or hepatobiliary pathology. 2, 4, 3

For Left Lower Quadrant Pain:

• CT abdomen and pelvis with IV contrast has 98% diagnostic accuracy for diverticulitis and detects complications (abscess, perforation, fistula). 2, 4

For Non-Localized or Diffuse Pain:

• CT abdomen and pelvis with IV contrast is the imaging of choice, changing the primary diagnosis in 51% of cases and altering admission decisions in 25% of patients. 1, 2, 4, 3
• Never order CT pelvis alone—it provides insufficient coverage and must be combined with abdominal imaging. 1
• Always use IV contrast unless evaluating for urolithiasis—non-contrast CT misses inflammatory, vascular, and solid-cystic lesions. 1

Gynecologic-Specific Considerations in Young Women

Even with negative β-hCG, consider non-pregnancy gynecologic pathology: 1, 6, 3

• Pelvic inflammatory disease (PID): Initiate empiric broad-spectrum antibiotics immediately if minimum criteria are met (uterine + adnexal + cervical motion tenderness), covering N. gonorrhoeae, C. trachomatis, gram-negative bacteria, anaerobes, and streptococci. 1
  • Do not require multiple criteria before treating—requiring two or more findings reduces sensitivity and allows permanent reproductive damage. 1
  • Obtain cervical cultures for gonorrhea/chlamydia to guide partner treatment, but do not delay antibiotics. 1
• Ovarian torsion: Urgent surgical consultation if ultrasound shows enlarged ovary with decreased/absent Doppler flow. 1, 6
• Hemorrhagic or ruptured ovarian cyst: Transvaginal ultrasound with Doppler is diagnostic. 1, 6
• Endometriosis complications: Consider if history of dysmenorrhea or chronic pelvic pain. 6

Critical Pitfalls to Avoid

• Never skip β-hCG testing—this is the single most important initial test in any woman of reproductive age with abdominal pain. 1, 2, 4, 3
• Do not use CT as first-line for suspected gynecologic causes when β-hCG is positive—ultrasound provides equivalent or superior accuracy without radiation. 1, 3
• Do not dismiss mild or atypical symptoms—many cases of PID, appendicitis, and ovarian torsion present with nonspecific findings. 1
• Do not over-rely on normal laboratory values early in disease—leukocytosis may be absent in early appendicitis or PID. 2, 4
• Do not order plain radiographs routinely—they have limited diagnostic value in most patients with abdominal pain. 4
• Do not forget to examine for hernias at surgical scars and orifices—incarcerated hernias are easily missed. 2

Specific Management by Diagnosis

• Ectopic pregnancy: Immediate obstetric consultation for methotrexate versus surgical management. 1
• Appendicitis: Surgical consultation for appendectomy. 2, 3
• PID: Empiric antibiotics as above, with admission if tubo-ovarian abscess, pregnancy, severe illness, or inability to tolerate oral therapy. 1
• Ovarian torsion: Urgent surgical detorsion to preserve ovarian function. 1, 6
• Mesenteric ischemia: Immediate vascular surgery consultation and CT angiography. 2, 4