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

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.

To determine the post-test probability that men in the community with raised plasma ferritin concentrations are hazardous drinkers.

The subjects were 152 men, randomly selected from a city's electoral 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. This 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 hazardous drinker (sensitivity) to the probability of obtaining a raised plasma ferritin concentration in a non-hazardous drinker (1-specificity)) was calculated for different plasma ferritin cut off points.

A plasma ferritin level of > 652 micrograms/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 micrograms/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.

Inquiries could usefully be made into the alcohol consumption of men with a plasma ferritin concentration > 652 micrograms/l, as approximately one in three would admit to drinking hazardously.