What fluid is concentrated using membrane filtration?

Cerebrospinal fluid is the correct answer because it is often analyzed in cytological studies to diagnose various conditions affecting the central nervous system. Membrane filtration is a technique used in laboratory settings to concentrate cells or other components present in small volumes of fluids. In the case of cerebrospinal fluid, which is normally a clear, colorless liquid surrounding the brain and spinal cord, using membrane filtration allows for the concentration of cells, proteins, and other components that may indicate the presence of disease, such as infections or cancers.

This method is particularly important because the volume of cerebrospinal fluid collected during a lumbar puncture is relatively small, and concentrating it enables detailed examination and enhances detection of abnormal cells. Other fluids, such as blood plasma, urine, or saline solution, do not typically require this specific concentration method in the same diagnostic context as cerebrospinal fluid. While they may be analyzed in cytology, they often have different preparation techniques or requirements based on the specific components being evaluated.