A 17-year-old female presents to the emergency department with a 6-hour history of acute-onset right lower quadrant abdominal pain. The pain is sharp, constant, and radiates to her back. She also reports associated nausea and vomiting. She denies any fever, diarrhea, or changes in bowel habits. Her last menstrual period was 2 weeks ago and was normal.

On physical exam, she appears uncomfortable and is guarding her abdomen. Her vital signs are: temperature 38.2°C, heart rate 110 bpm, respiratory rate 18 breaths/min, and blood pressure 110/70 mmHg. Abdominal exam reveals tenderness to palpation in the right lower quadrant, with rebound tenderness and guarding. No masses or organomegaly are appreciated. Pelvic exam is deferred due to the patient's discomfort.

Significant Positives & Negatives For Differentials

Abdominal Pain in a Teenage Female

Positives:

• Acute onset of abdominal pain
• Localized right lower quadrant pain
• Associated nausea, vomiting
• Fever

Negatives:

• Absence of altered bowel habits
• No menstrual irregularities

Pelvic Inflammatory Disease

Positives:

• Lower abdominal pain

Negatives:

• Absence of vaginal discharge
• No cervical motion tenderness
• No adnexal tenderness
• Normal vital signs

Ovarian Cyst/Torsion

Positives:

• Acute onset of unilateral lower abdominal pain
• Associated nausea, vomiting

Negatives:

• Bilateral lower abdominal pain
• Absence of palpable mass
• No adnexal tenderness

Appendicitis

Positives:

• Acute onset of right lower quadrant pain
• Nausea, vomiting
• Fever
• Rebound tenderness
• Guarding

Negatives:

• None

Based on the patient's presentation, with acute-onset right lower quadrant abdominal pain, associated nausea/vomiting, fever, and physical exam findings of rebound tenderness and guarding, the most likely diagnosis is appendicitis. Further workup, including laboratory tests and imaging, would be warranted to confirm the diagnosis and guide appropriate management.