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A 40 year old G1P0 woman at 36 weeks gestation presents to the emergency department with nausea, vomiting, and upper abdominal epigastric pain. She has a history of gestational diabetes and obesity, but no other medical problems. Her symptoms had worsened over several days, accompanied by headache, which she associates with not being able to keep any food down. She adamantly refuses any X-rays or scans because of her pregnancy.

Vitals are heart rate 90, blood pressure 145/91, respiratory rate 16, oxygen saturation 98% on room air. On exam, you note a normal gravid uterus, negative McBurney's sign, no rebound or guarding, but mild epigastric tenderness to palpation. You also note peripheral edema. Laboratory tests show an elevated hematocrit, a platelet count of 90,000/microL, a creatinine of 1.4 mg/dL.

Challenge: What test is shown in the image above and why do you order it?

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