Animal studies have shown that Lp(a) may directly contribute to atherosclerotic damage by increasing plaque size, inflammation, instability, and smooth muscle cell growth. Genetic data also support the theory that Lp(a) causes cardiovascular disease. The European Atherosclerosis Society currently recommends that patients with a moderate or high risk of cardiovascular disease should have their Lp(a) levels checked. Any patient with one of the following risk factors should be screened:  If the level is elevated, treatment should be initiated to bring the level below 50 mg/dL. In addition, the patient's other cardiovascular risk factors (including LDL levels) should be managed optimally. Apart from the total Lp(a) plasma concentration, the apo(a) isoform might be an important risk parameter as well. Prior studies of the relationship between Lp(a) and ethnicity have shown inconsistent results. Lp(a) levels seem to differ in different populations. For example, in some African populations, Lp(a) levels are higher on average than in other groups, so that using a risk threshold of 30 mg/dl could classify over 50% of the individuals as higher risk. Some part of this complexity may be related to the different genetic factors involved in determining Lp(a) levels. One recent study showed that in different ethnic groups, different genetic alterations were associated with increased Lp(a) levels. More recent data suggest that prior studies were underpowered. The Atherosclerosis Risk in Communities (ARIC) Study followed 3467 African Americans and 9851 whites for 20 years. The researchers found that an elevated Lp(a) conferred the same risk in each group. African Americans had roughly three times the level of Lp(a), however, and Lp(a) also predicted an increased risk of stroke. Approximate levels of risk are indicated by the results below, although at present there are a variety of different methods by which to measure Lp(a). A standardized international reference material has been developed and is accepted by the WHO Expert Committee on Biological Standardization and the International Federation of Clinical Chemistry and Laboratory Medicine. Although further standardization is still needed, development of a reference material is an importance step toward standardizing results. Lipoprotein(a) - Lp(a)  Lp(a) appears with different isoforms (per kringle repeats) of apolipoprotein; 40% of the variation in Lp(a) levels when measured in mg/dl can be attributed to different isoforms.