ICMJE recommends in Section 3.g.ii. on Reference style and format that:
"References should follow the standards summarized in the NLM's International Committee of Medical Journal Editors (ICMJE) Recommendations for the Conduct, Reporting, Editing and Publication of Scholarly Work in Medical Journals: Sample References webpage and detailed in the NLM's Citing Medicine, 2nd edition."
See www.nlm.nih.gov/bsd/uniform_requirements.html and www.ncbi.nlm.nih.gov/books/NBK7256/