Final answer:
Fluid from a transudate pleural effusion, commonly resulting from congestive heart failure, has low protein content and a low specific gravity of 1.003 to 1.018, distinguishing it from the more protein-rich and denser exudate fluids.
Step-by-step explanation:
Serum characteristics of a transudate such as a pleural effusion from congestive heart failure (CHF) include low protein content and a specific gravity typically less than 1.020. Compared to exudates, transudate fluids result from increases in hydrostatic pressure or decreases in osmotic pressure in the vessels, rather than from increased vascular permeability.
In the case of CHF, the increase in hydrostatic pressure within pulmonary capillaries causes fluid to accumulate in the pleural space, leading to pleural effusion. This fluid is usually watery with low viscosity and its specific gravity is between 1.003 and 1.018, which is less than the specific gravity of exudates. Serum proteins such as albumin are also lower in concentration in transudates compared to exudates. These features help differentiate transudative pleural effusions, often related to systemic conditions like CHF, from exudative effusions caused by local factors such as infections or malignancies.