An 18-year-old female presents to casualty with
abdominal pain. On examination she is in distress, she has a pulse rate o f
130 beats per minute her blood pressure is 80/50 her respiratory rate is 38
per minute. Abdominal examination revealed generalised tenderness.
Her blood results are as follows:
Sodium 110 mmol/l
Potassium 5.5 mmol/l
Urea 11 mmol/l
Which of the following tests will determine the cause
of this patientís condition?