Serum Anticholinergic Activity in Hospitalized Older Persons with Delirium: A Preliminary Study

OBJECTIVE: To evaluate the relationship between total serum anticholinergic activity (SAA) and the presence or absence of delirium in older hospitalized persons on general medical wards. DESIGN: Case-control study and within-subjects repeated-measures in recovered delirious patients. SETTING: Minneapolis Veterans Affairs Medical Center medical wards. PARTICIPANTS: Eleven male delirious patients (DSM-III-R criteria) aged 60 or older and 11 comparably aged male nondelirious controls. MEASUREMENTS: Radioreceptor bioassay of total SAA using tritiated quinuclidinyl benzilate (QNB) binding to muscarinic receptors. Results are expressed in terms of atropine equivalents (nM). MAIN RESULTS: Mean SAA was significantly elevated in the delirious group (mean +/- SD = 6.05 +/- 2.97 nM atropine equivalents) compared with the controls (3.38 +/- 2.49; t(20) = 2.28, P < .05). At study entry, mean SAA was significantly higher in delirious subjects whose symptoms eventually resolved completely (mean +/- SD = 7.77 +/- 2.37) compared with subjects whose delirious symptoms persisted (3.99 +/- 2.30; t(9) = 2.68, P < .05). All six patients in whom delirium resolved completely had a decrease in serum anticholinergic activity when measured during delirium (7.77 +/- 2.37) and after symptom resolution (3.92 +/- 2.61; t(5) = 3.29, P < .05). CONCLUSIONS: Our findings suggest that serum anticholinergic activity may play a role in delirium in medical inpatients. The relationships between SAA and delirium in medical patients and between total SAA and medication use warrant further study.