A 25-year-old female client comes to the facility complaining of abrupt and severe lower abdominal pain, which radiates to the lower back and thighs. The client says the pain usually lasts for 20 minutes, resolves and then comes back again. The pain has started 12 hours before the consult. The client also reports vomiting, excessive sweating and constipation. Assessment findings include fever, tachycardia and tenderness over the lower abdominal region, with greater pain reported on the side. Urine human chorionic gonadotropin test is negative. Which of the following diagnostic tests is ordered for further evaluation and diagnosis?