Use of the abbreviated mental test to detect postoperative delirium in elderly people.

We investigated the validity of the abbreviated mental test (AMT) as a guide to the diagnosis of delirium in 100 patients aged more than 65 yr. Patients were assessed using the AMT on the day before and on the third day after operation. Fifteen patients were delirious on the third postoperative day; 10 of 43 patients undergoing orthopaedic surgery and five of 57 patients undergoing non-orthopaedic surgery. Delirium developed in four of 16 patients with a preoperative AMT score less than 8 and in 11 of 84 patients with a preoperative AMT score of 8 or more. Patients who developed delirium had a greater decline in AMT score (mean 2.7 (SD 0.9)) than patients who did not develop delirium (0.7 (1.0)) (P < 0.001). The sensitivity and specificity of a decline in AMT score of 2 or more points after surgery for diagnosis of postoperative delirium were 93% and 84%, respectively.