**Author details**

As a consequence of these challenges, a group of experts in the field vent together that tackled these problems by propagating various reference standards and methods. We also participated in this survey using our in-house laboratory methods and antibodies [40]. A major problem that came out from this study was the different reference materials used in the assays. Even the use of the WHO/IFCC Reference Material as a common calibrator did not result in

We consider most of the considerations, based on theoretical grounds, of little importance in commercial routine clinical assays. There are three important questions that need to be solved: (1) What methods are apo(a)-isoform insensitive? (2) How can be units in mg/dl be transformed

Considering all these puzzles, we propagate the following: Our preferred commercial assays are based on latex-enhanced immune-nephelometry or -turbidimetry. This is based on the consideration that the size of latex particles in comparison to the size of Lp(a) is very high and the size polymorphism of apo(a) becomes negligible. In addition, the latter methods are highly precise and may be applied in high-throughput. ELISA and DELFIA methods may be isoforminsensitive if monoclonal antibodies are used that recognize only one epitope on apo(a).

Another possibility that still needs confirmation is to assay apo(a) fragments in urine. In urine, apo(a) fragments are secreted by a mechanism that has not been fully explored so far. These fragments consist mostly of repetitive K-IV structures of different lengths and thus what is measured accurately even by the use of polyclonal antibodies is the concentration of K-IVs, mostly of type 2, that have been shown to correlate significantly with the plasma Lp(a) concentration [42]. In the work cited in ref. [42], we could actually show that the discriminatory power of urinary apo(a) fragments is at least as good—if not even better—than that of plasma

**12. Should Lp(a) levels be expressed as mass units or molar units?**

This question is partly academic since there is, at the moment, no validated commercial assay on the market that gives accurate and reliable molar values. One must also consider that most of the individuals are heterozygous, i.e. they have 2 kinds of Lp(a) particles in their blood with quite large differences in the molecular mass. In our laboratory, we use mass values since the majority of the published epidemiological studies publish their values in mg/dl or mg/L. In addition, the cutoff values propagated in the Consensus Report of the European Atheroscle‐

Keeping in mind that not only the molecular mass but also the composition of Lp(a) varies quite remarkably, we must think practicable for the time being. Assuming a molecular mass

into nmol/L? (3) What are the cutoff levels to be adopted for risk stratification?

**11. What needs to be considered in measuring Lp(a)?**

satisfactory harmonization of Lp(a) values [41].

148 Lipoproteins - From Bench to Bedside

Lp(a).

rosis Society are given in mg/dl.

Indumathi Chennamsetty1\* and Gert M. Kostner2

