Serum anticholinergic activity changes with acute illness in elderly medical patients

Background. Elevated serum anticholinergic activity levels have been associated with delirium in cross-sectional studies of ill older persons. This study used serial measures of serum anticholinergic activity levels to determine whether these levels change following illness resolution, and if such changes are specific to those with delirium. Methods. Twenty-two nursing home residents with a febrile illness had serum specimens drawn and were evaluated for the presence of delirium during the acute illness and at I-month follow-up. Delirium was diagnosed using the Confusion Assessment Method. Serum anticholinergic activity was determined using a previously described radionuclide competitive-binding assay. Results. Delirium was present during illness in 8 of 22 subjects (36%), and had resolved by 1-month follow-up in all but one resident. Serum anticholinergic activity levels were significantly higher during illness than at 1-month follow-up in both the delirious (0.69 +/- 0.85 nM atropine equivalents/200 mu L sample versus 0.10 +/- 0.16; p = .06) and non-delirious (0.65 +/- 0.51 nM atropine equivalents/200 mu L sample versus 0.08 +/- 0.12; p < .001) groups. Medication changes did not seem to be related to changes in serum anticholinergic activity. Conclusions. In older nursing home residents with a fever, serum anticholinergic activity appears to be elevated during illness, and declines following recovery from illness. This effect does not seem to be specific to those residents with delirium, nor does it seem related to medication changes.