Lipoprotein(a) – now orderable for patient testing and for research use
In early 2023, we completed validation of the Randox immunoturbidimetric assay for lipoprotein(a). Lipoprotein(a) [Lp(a)] is now recognized as a lipoprotein that is an independent risk factor for coronary heart disease, stroke, and calcific aortic valve stenosis (1-5). It is estimated that 20% of the population has elevated levels of Lp(a) (5). Drugs to lower Lp(a) levels are currently in Phase III clinical trials and show tremendous promise for lowering Lp(a) levels in humans.
Much discussion has occurred through the years about units of reporting for Lp(a). The assay we utilize allows reporting in nmol/L units, the preferred reporting units by several professional groups (2-5). Since this was FDA approved only in mg/dL units, we have performed additional validation which is summarized below. The Randox assay is licensed from Denka Seiken which uses five-point calibrators that eliminate some heterogeneity issues observed with other assays on the market.
Clinical Use
Lp(a) can be used in examining atherosclerotic cardiovascular disease risk. Levels are predominantly genetically determined and believed to be relatively stable throughout life. Various agencies have different suggestions of what populations to test and what cut-offs to use for risk assessment (1-5). Our lab uses ≤ 75 nmol/L as its reference range with the following statement added to patient results:
“A Lp(a) level >100 nmol/L is considered as an atherosclerotic cardiovascular disease (ASCVD) risk-enhancing factor by the National Lipid Association and corresponds to the 80th population percentile in Caucasians. The corresponding 80th population percentile in African Americans is 150 nmol/L, but it is currently unclear whether a different risk threshold should be applied (J. Clin. Lipidology 2019; 13:374-392).”
Table 1. Randox Lipoprotein(a) Performance Parameters in our Lab
| Analytical Measuring Range | 5.0 – 206.0 nmol/L |
| Within-Run Precision | < 2.0% CV |
| Between-Run Precision | ≤ 3.8% CV |
| Accuracy | Acceptable when compared with Quest laboratories method. |
| Acceptable Sample Type | Serum, Na- or K-EDTA plasma, Li- or Na-heparin plasma, citrated plasma |
| Sample Stability | 2 days at room temperature; 10 days at 4-8 oC; 4 weeks at – 20 oC; Stable for 3 freeze-thaw cycles. |
| Minimal Sample Size | 150 µL (500 µL or more preferred) |
References
1) SS Virani et al. Global think tank on the clinical considerations and management of lipoprotein(a): The top questions and answers regarding what clinicians need to know. Progress in Cardiovascular Diseases 2022; 73: 32-40. https://doi.org/10.1016/j.pcad.2022.01.002
2) AHA Council on Arteriosclerosis. Lipoprotein(a): A genetically determined, causal, and prevalent risk factor for atherosclerotic cardiovascular disease. Arterioscler Thromb Vasc Biol 2022; 42:e48-e60. https://doi: 10.1161/ATV.0000000000000147
3) J Cegla, M France, SM Marcovina, and RDG Neely. Lp(a): When and how to measure it. Ann Clin Biochem 2021; 58:16-21.
4) EAS and EFLM Joint Consensus Initiative. Quantifying atherogenic lipoproteins for lipid-lowering strategies. Clin Chem Lab Med 2020; 58:496-517.
5) DP Wilson, TA Jacobson, PH Jones, et al. Use of Lipoprotein(a) in clinical practice: A biomarker whose time has come. J Clin Lipidology 2022; 16:e77-e95. (National Lipid Association statement)
C-reactive Protein
Our lab has offered high sensitivity C-reactive protein (hsCRP; CPT code: 86141) for many years. We also offer the regular C-reactive protein (CRP; CPT code: 86140) available for clinic or research testing. A comparison measuring ranges and reference ranges between these two is shown below. The CRP (86140) is typically ordered as a measure of inflammation or infection, while the hsCRP can be used for cardiovascular risk assessment.
| Test | Analytical Measuring Range | Reference Range and Guidelines |
| hsCRP CPT# 86141 | 0.15 – 20.00 mg/L (with dilutions up to 300 mg/L) | Cardiovascular Risk Assessment: <1.0 mg/L Low risk; 1.0 – 3.0 mg/L Average risk; >3.0 mg/L High risk |
| CRP CPT# 86140 | 3 – 350 mg/L | < 5 mg/L |