The Ongoing Utility of lipoprotein lipase activity in diagnosing familial Chylomicronemia Syndrome.

Objective: Given that lipoprotein lipase (LPL) activity assays are not standardized for clinical use, we aimed to define reference values applicable to our clinical setting and identify a cut-off point to help distinguish Familial Chylomicronemia Syndrome from Multifactorial Chylomicronemia Syndrome, particularly in patients with inconclusive genetic findings. Methods: We evaluated 28 patients with a history of TG levels above 880 mg/dL (10 mmol/L), and assessed their likelihood of FCS using the Moulin score. LPL activity was measured in post-heparin plasma using a radiometric assay. Thirty normotriglyceridemic controls were used to define reference values. Genetic testing for FCS canonical genes and lipid profile was performed in all sHTG patients. Results: The reference value for LPL activity was 33.3 (18.7-70.3) mIU, with a cut-off of 8.42 mIU (25 % of the median of NTG) to distinguish FCS from MCS. Eighteen patients without genetic variants in canonical genes, a Moulin score <9 and LPL activity >25 % of NTG, were classified as MCS. Five genetic diagnosed FCS patients, with a Moulin score>10 presented LPL activity <25 % of NTG. Four patients with inconclusive genetic results and a Moulin score>10 were classified as FCS according to LPL activity. Conclusion: LPL activity in patients with sHTG could be useful for differentiating FCS and MCS, particularly in patients with ambiguous or negative genetic findings, highlighting the need for specialized laboratory support in diagnostics.