Post-test probability that men in the community with raised plasma ferritin concentrations are hazardous drinkers

Background-Raised plasma ferritin concentrations occur unexpectedly during iron studies done by primary care physicians. Plasma ferritin concentration has been positively associated with alcohol use among men. Aim-To determine the post-test probability that men in the community with r aised plasma ferritin concentrations are hazardous drinkers. Methods-The subjects were 152 men, randomly selected from a city's electora l roll. Nineteen (12.5 (2.7)%, mean (SEM)) admitted to drinking hazardously . The pretest probability of a man being a hazardous drinker was 0.125, Thi s was converted to pretest odds of 0.14. The likelihood ratio (the ratio of the probability of obtaining a raised plasma ferritin concentration in a h azardous drinker (sensitivity) to the probability of obtaining a raised pla sma ferritin concentration in a nonhazardous drinker (1-specificity)) was c alculated for different plasma ferritin cut off points. Results-A plasma ferritin level of > 652 mu g/l gave the largest likelihood ratio, 4.16. Post-test odds were obtained by multiplying the pretest odds (0.14) by the Likelihood ratio (4.16). A plasma ferritin level of > 652 mu g/l had a post-test odds for a man being a hazardous drinker of 0.58. This was converted to a post-test probability of 0.37. Conclusions-Inquiries could usefully be made into the alcohol consumption o f men with a plasma ferritin concentration > 652 mu g/l, as approximately o ne in three would admit to drinking hazardously.