A 57-year-old patient complains of dyspnea at rest. The patient presents with orthopnea, acrocyanosis, bulging cervical veins. On percussion: dull sound over the lower lung segments; on auscultation: no respiratory murmurs. Heart rate is 92/min. Right-sided cardiac dilatation is observed. The liver is enlarged by 7 cm. Shins are swollen. Pleural effusion is suspected. What indicator would confirm the presence of transudate in this case?