A 48-year-old patient complains of weakness, subfebrile temperature, aching pain in the kidney region. These presentations turned up three months ago after hypothermia. Objectively: kidneys are painful on palpation, there is bilaterally positive Pasternatsky's symptom. Urine test res: acid reaction, pronounced leukocyturia, microhematuria, minor proteinuria - 0,165-0,33 g/l. After the urine sample had been inoculated on conventional media, bacteriuria were not found. What research is most required in this case?