Diagnostic yield of laboratory testing in hospitalized older adults with altered mental status

Altered mental status (AMS) is a common cause of hospitalization among older adults, with a wide range of potential etiologies. However, the diagnostic and therapeutic yield of routine laboratory testing in such patients is unknown.

In a retrospective cohort of inpatient hospital admissions to a large academic medical center from 2017 to 2022 of patients 65 years and older for whom the admitting diagnosis was AMS, we assessed laboratory testing for thyroid stimulating hormone (TSH), syphilis, vitamin B12, folate, vitamin C, vitamin D, zinc, niacin, and thiamine. We calculated the frequency of testing, rate of abnormal results, and rate of follow-up treatment.

Of the 3169 patients, 2312 (73 %) received at least one designated lab, and overall, 12 % of labs were abnormal. Labs varied in frequency of use (0.2 % for niacin-66 % for TSH) and rate of abnormality (0 % for niacin-71 % for zinc). 16 % of abnormal index labs led to a new prescription at discharge. The most common tests - TSH, folate, and B12- were of relatively low diagnostic and therapeutic utility. Tests that were less common-zinc, vitamin D, and vitamin C-were more commonly abnormal. 3.8 % of patients tested for syphilis had abnormal results, and 72 % of patients with an abnormal result received treatment with penicillin during the index hospitalization.

These analyses suggest that commonly obtained labs in the workup of AMS have varied diagnostic and therapeutic utility. The contribution of observed laboratory abnormalities to a patients' AMS warrants further study to improve the delivery of high-value care.