Biomarkers for diseases like cancer, heart failure, viral infections or metabolic disorders are present in body fluids like whole blood or serum. By using an immunoassay with specific labelled antibodies these biomarkers can be selectively bound to a solid phase and detected. For electrochemiluminescent (ECL) detection, the label contains an organometallic compound like Ru(2,2′-bipyridine)32+ capable of emitting light after undergoing a series of electrochemically induced redox reactions with a coreactant like tripropylamine. ECL efficiency can be improved by adding ECL enhancing compounds like carbonic acid amides or by optimization of the ECL label for example by substitution of the bipyridine rings, by polymerization or by exchanging ruthenium by iridium. Furthermore, also the linker connecting the ECL label and the antibody and the conjugation method has an influence on assay performance. Roche Diagnostics cobas e analyzers automate immunoassays based on ECL detection and together with the Elecsys® assays, which are available for more than 100 different biomarkers, they have become widely used for in-vitro diagnosis, because they allow high throughput, sensitive and precise quantification of biomarkers in small volumes of patient samples.