[1] Univ Oslo, Inst Hlth & Soc, Dept Gen Practice, Oslo, Norway
[2] Univ Oslo, Inst Clin Med, Fac Med, Oslo, Norway
[3] Oslo Univ Hosp, Dept Endocrinol Morbid Obes & Prevent Med, Oslo, Norway
[4] Haraldsplass Deaconess Hosp, Norwegian Qual Improvement Lab Examinat, Bergen, Norway
[5] Univ Bergen, Dept Global Publ Hlth & Primary Care, Bergen, Norway
[6] Stavanger Univ Hosp, Dept Med, Stavanger, Norway
[7] Nordland Hosp, Dept Med, Bodo, Norway
[8] Haukeland Hosp, Dept Clin Biochem & Pharmacol, Bergen, Norway
[9] Univ Oslo, Inst Hlth & Soc, Dept Gen Practice, Gen Practice Res Unit AFE, Post Box 1130, N-0318 Oslo, Norway