Received: 7 November 2017
Accepted: 19 February 2018
First Online: 3 March 2018
Compliance with ethical standards
: P.S. and L.S. are employees of jung diagnostics GmbH, Hamburg, Germany. This did not bias their work, as they have no financial interest in the results of this study. All other authors declare that they do not have any potential conflict of interest concerning this manuscript.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
: As the present study was retrospective in nature, formal consent was not required.