Milky pleural effusion in a neonate and approach to investigating chylothorax

Neonatal chylothorax is a rare presentation leading to significant respiratory distress, thus requiring timely diagnosis. A preterm neonate was resuscitated and ventilated, following which she clinically improved but subsequently developed respiratory distress with a right-sided pleural effusion. Interestingly, thoracentesis fluid appeared ‘milky’ with elevated triglycerides and lymphocytes, suggesting chylothorax. As fluid triglyceride level was lower than the established diagnostic criterion for chylothorax (1.24 mmol/L), a high fluid-to-serum triglyceride ratio was used as a surrogate diagnostic marker, later confirmed by lipoprotein electrophoresis. As observed in the index patient, a critically ill neonate would have a lower-than-average fat intake leading to less chylomicron production, thus lower triglyceride levels in chyle than expected, which may still fail to meet the amended cut-off limit. This case highlights the challenges in diagnosing neonatal chylothorax due to the lack of age-specific triglyceride levels in chyle and low oral fat intake in critically ill patients.