Sometimes all it takes is telling your doctor the type of injury, describing your symptoms, and getting a physical exam.
Your doctor can also measure pressure inside the body compartment. She'll insert a needle into the area while an attached monitor records the pressure. Or she can insert a plastic catheter to monitor the pressure in your bladder. High bladder pressure, along with other signs means abdominal compartment syndrome is likely.
Laboratory and imaging tests can support the diagnosis. But no single test other than a direct pressure measurement can confirm the diagnosis.