Corrections
Update
BMJ 2020; 369 doi: https://doi.org/10.1136/bmj.m1617 (Published 19 May 2020) Cite this as: BMJ 2020;369:m1617This NICE guideline summary (BMJ 2012;344:1163, doi:10.1136/bmj.e3979) has now been superseded by a summary of updated guidance at www.bmj.com/content/369/bmj.m1565.