Tomson 1998.

Methods	RCT: brief intervention versus usual care. ITT: unclear.
Participants	Setting: Sweden, general practice health centre. Participants: 25 to 54 years with GGT > 0.89 microkatals/L; screened by health check including GGT; excluded if chronic alcoholic. Number randomised = 222. The following data is for N = 75, who were not excluded and then were followed up: 81% male; mean age = 45.2 years; 73% blue collar, 27% white collar. At baseline: mean weekly consumption given at baseline only for intervention group = 337 g; mean S‐GGT = 1.7 microkatals/L.
Interventions	Intervention group (N = 100) had an appointment with a nurse to establish whether the laboratory finding could be explained by excess alcohol intake. The nurse had experience from outpatient care of alcoholics and made a ‘general lifestyle and health survey interview’. The assessment also included self‐reported alcohol consumption and the CAGE questionnaire. Patients responding "yes" to two or more of the four questions were classified as positive. The nurse discussed those with an unclear elevation of GGT with the GP, who sometimes recommended further examination and:or laboratory investigations. Participants classified as high consumers of alcohol (280 and 210 g 100% alcohol per week for men and women, respectively) were offered two more consultations with the nurse during the intervention year. The consultations focused on lifestyle in general and alcohol consumption in particular. Factors that facilitated or made controlled drinking more difficult were discussed in an empathic way. GGT was used as a biochemical feedback at follow‐up. Control group (N = 122) recommended an appointment with the GP. The participants were asked about diseases and ongoing medication. They were told that the most common reasons for an elevated GGT had to do with eating and drinking habits and drug use. They were asked about their own thoughts concerning the reason for their elevated GGT. When the spontaneous response was that their alcohol consumption was a plausible explanation, the GP accepted this without comment. In the other cases the GP also made a clinical and an extended laboratory investigation. Those classified as high consumers were not given any advice about how to reduce their drinking, but were told that a follow‐up was planned in one to two years.
Outcomes	GGT measured at one and two years. Data about sickness allowance days one year before, during, and one year after the intervention, and notations in the social services records were collected. The number of visits to the health centre for reasons other than alcohol intervention (intervention group), days of hospital care, and deaths up to two years after intervention were followed. Assessed at one and two years.
Funding source	Not reported.
Declaration of interests	Not reported.
Notes	Loss to follow‐up: Intervention group: 70/100 (70%). Control group: 77/122 (63%). Randomisation (n = 222) then assessment & exclusion (leaving n = 75 who actually had the intervention or control sessions).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Date of birth used for randomisation (as reported in Kristensen 1983).
Allocation concealment (selection bias)	Unclear risk	No information on how allocation was concealed.
Blinding of treatment providers	Low risk	Different treatment providers interacted with the different arms (nurse for intervention group, doctor for control group: "the GP was anxious not to use the consultation with the control group as an intervention but to try to rule out an elevated GGT due to a serious disease" ‐ p. 189).
Blinding of participants	Low risk	Recruitment letter to participants does not discuss alcohol as a reason for attendance but just that elevated blood test needed a follow‐up.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not clear whether outcome assessors were blinded.
Incomplete outcome data (attrition bias) All outcomes	High risk	Loss to follow‐up > 30%.
Selective reporting (reporting bias)	Low risk	Outcomes specified in methods are reported.