For 3 days, a 28-year-old female patient had had the body temperature increase up to 38°C, weakness, poor appetite, nausea, a single vomiting. On the 4th day the temperature was normal, the condition improved, but the jaundice developed. Objectively: moderate ictericity of skin, +3 cm enlarged liver of elastic consistency. Ortner's, Kehr's and Voznesensky's symptoms are negative. What test will verify the diagnosis?