Introduction: Elevated levels of lipoprotein(a) (Lp[a]) are associated with an increased risk for cardiovascular disease. Currently, promising Lp(a) – lowering therapeutics are under investigation. In clinical practice, Lp(a) is often measured only once assuming that it does not change nor fluctuate over time. However, several studies in adults have reported substantial within-person fluctuations of Lp(a). Therefore, we evaluated whether Lp(a) remains constant with increasing age and determined the within-person fluctuation of Lp(a) levels over time.  
Methods: All children that visited the pediatric Lipid Clinic of the Academic Medical Center (Amsterdam) between 1989 and 2017 were eligible. These children were referred for a tentative diagnosis of inherited dyslipidemia. We included those who were under 18 years at their first Lp(a) measurement. Mixed models were used to evaluate changes over time and within-person fluctuations of Lp(a). 
Results: We included 2,813 children (mean [standard deviation] age: 10.1 [3.6] years) with a median (interquartile range) Lp(a) level of 143 (62 – 380) mg/L. In 1,255 children, more than one measurement was available. Percental increases in Lp(a) levels compared to a reference age of 10 years were 1.2% (95% CI: 0.8-1.5), 5.9% (95% CI: 4.2-7.7), 12.2% (95% CI: 8.5-16) and 25.9% (95% CI: 17.7-34.6) at the age of 11, 15, 20 and 30 years, respectively. The intra-individual variability of Lp(a) was 37.4% (95% CI: 36.2-38.7) at any age during our inclusion period.  
Conclusion: Our results suggest that Lp(a) levels do not remain constant from childhood into adulthood; in fact, these levels increase exponentially with increasing age. Moreover, Lp(a) exhibits considerable fluctuations over time in the individual patient. Measuring Lp(a) only once in life might therefore lead to over- or underestimation, possibly resulting in over- or under treatment. Therefore, we recommend measuring Lp(a) more than once in order to more accurately assess the Lp(a) level in the individual patient.

07 - LIPOPROTEIN(A) LEVELS OVER TIME: A LONG-TERM FOLLOW-UP STUDY OF A LARGE COHORT OF CHILDREN