Chapter 23: Cerebrospinal, Pleural and Ascitic Fluids

Cerebrospinal, Pleural and Ascitic Fluids outlines the physiology of cerebrospinal fluid (CSF), produced by the choroid plexuses and circulated through the ventricular system to support the central nervous system and facilitate waste removal. The text stresses the necessity of comparing CSF concentrations to plasma, as deviations in glucose and protein levels are primary indicators of underlying pathology; for instance, significantly reduced glucose often signifies bacterial or tuberculous meningitis, while elevated protein levels can indicate inflammation, spinal blockages known as Froin’s syndrome, or local immunoglobulin synthesis. Specialized tests such as spectrophotometry for xanthochromia are used to distinguish subarachnoid hemorrhage from traumatic lumbar punctures, while the detection of tau protein (asialotransferrin) serves as a unique marker for identifying CSF leaks in nasal discharge. Additionally, the material covers the classification of pleural effusions into transudates and exudates, utilizing Light’s criteria—which evaluates protein and lactate dehydrogenase (LDH) ratios—to differentiate between systemic conditions like heart failure and localized issues like malignancy or infection. Finally, the chapter discusses ascitic fluid analysis, emphasizing the serum-ascites albumin gradient (SAAG) as a superior diagnostic tool for identifying portal hypertension over traditional protein cut-offs, thereby aiding in the diagnosis of conditions such as cirrhosis, spontaneous bacterial peritonitis, and Meig's syndrome.