# Promising Novel Biomarkers in Cardiovascular Diseases
## 2 Common Detection Methods for Biomarker Analysis
However, besides ELISA other techniques for the quantification of H-FABP levels exist, such as proximity extension analyses (described elsewhere) [81], and latex enhanced turbidimetric immunoassay [82; 83]. The latter is based on latex particles that are coated with a monoclonal anti H-FABP antibody that bind the appropriate antigen in the sample and agglutinate. Thereafter, the light scattering caused by an increase in particle size is a measure of the H-FABP concentration (HiSens H-FABP turbidimetric immunoassay, HBI, Anyang, Korea) [84]. Randox Laboratories Limited (Crumlin, Co. Antrim, UK) provides a fully automated system that quantifies the protein's level within approximately 15 min [85; 86]. In comparison to the results gained by ELISA, immunoblotting assays reveal higher H-FABP levels with a greater area under the curve and superior prognostic information than ELISA [83]. In addition to that, several bedside rapid tests have already been established to provide quantitative results within a short time range: Cardiodetect(r) from Rennesens GmbH (Berlin, Germany) was the first H-FABP rapid test worldwide and is based on a chromatographic immunoreaction that detects the protein's level in the patients' whole blood with a threshold of 7 ng/mL [87; 88]. Further companies have then seized on this idea to improve the rapid clinical diagnosis of cardiac biomarkers, combining the two most important cardiac biomarkers, H-FABP and troponin I, in one single rapid test cassette. The combined tests are also based on the binding properties of the appropriate antigens with the specific antibodies that are provided on a nitrocellulose membrane (e.g., H-FABP and cTnI Combo Rapid Test Cassette by BioZEK B.V., The Netherlands, or MyoCheck(r) by Concile GmbH, Germany). GDF-15 is a highly prominent biomarker in CVD, thus reliable and reproducible test results are crucial for risk stratification and prognosis. Several studies have addressed the measurement of this biomarker using the research kits Quantikine [89; 90; 91; 92] and DuoSet [93; 94; 95; 96] ELISA from R&D Systems (Minneapolis, MN). However, some in vitro diagnostic assays for GDF-15 have already been developed, namely GDF-15/MIC-1 Human ELISA from BioVendor Laboratory Medicine (Modrice, Czech Republic) [97; 98; 99]. More recently, a relatively new methodology has emerged and already received the CE mark in the European Union. The automated electrochemiluminescence (Elecsys(r) immunoassay by Roche Diagnostics (Basel, Switzerland) is based on a sandwich immunoassay principle that may be performed with 35 \(\mu\)L of the patient's blood sample. Two incubation periods of only 9 min with automated washing steps in between make this a straightforward, rapid procedure requiring little personnel effort. The detection of the quantitative signal is achieved by measuring the antigen-antibody complexes via electrochemiluminescence using a cobase a analyser (Roche Diagnostics, Basel, Switzerland) [100; 101; 102]. Some studies, such as that of [PERSON] et al. [103], have compared serum or plasma GDF-15 levels gained by different available research and diagnostic kits. The results showed that GDF-15 concentrations measured by Elecsys assay correlated with those from ELISA. Additionally, it has been shown that the GDF-15 concentrations do not differ significantly in plasma or serum samples, respectively [90]. As for the other biomarkers mentioned, the sandwich ELISA procedure is also the method of choice for the measurement of peripheral suPAR concentrations. The most prominent and widely used kit certainly is the suPARnostic(r) ELISA by ViroGates (Birkered, Denmark). The kit is certified for in vitro diagnostics and is therefore valid for clinical use [104]. In contrast to the kits available for research use only, such as the Quantikine [105; 106; 107] and DuoSet [93; 95; 79] ELISA Kits from R&D Systems, the benefits of suPARnostic(r) ELISA include the time-to-result of only 1.5 h and the easy handling of the ready-to-use reagents.