Epidemiology of Intensive Care Patients Classified as a Third Sex in Australia and New Zealand

Abstract

BackgroundPatient sex affects treatment and outcomes in critical illness. Previous studies of sex differences in critical illness compared female and male patients. In this study we describe the group of patients classified as a third sex admitted to intensive care units (ICUs) in Australia and New Zealand. Research questionWhat are the admission characteristics and outcomes of ICU patients classified as belonging to a third sex group, compared to patients classified female or male? Study design and methodsRetrospective observational study of admissions to 200 ICUs, recorded in the Australia and New Zealand Intensive Care Society’s Adult Patient Database 2018–2022. We undertook mixed effect logistic regression to compare hospital mortality across the sex groups, adjusted for illness severity, diagnosis, treatment limitation, year and hospital. ResultsWe examined 892,161 admissions, of whom 525 (0.06%) were classified as third sex. Patients classified as third sex were represented across all diagnostic categories, jurisdictions, and hospital types. On average, they were younger than the groups classified as female (59.2+/-20.0 years vs 61.3+/-18.4 years, p=0.02) or male (63.2+/-16.7 years, p<0.001). Patients classified as third sex were more likely to be admitted following orthopedic surgery (10.1% third sex admissions (95% CI 7.7-13.0%) vs 6.2% female (95% CI 6.1-6.3%); 4.8% male (95% CI 4.7-4.9%)) and drug overdose (8.8% third sex admissions (95% CI 6.5-11.5%) vs 4.2% female (95% CI 4.1-4.2%); 3.1% male (95% CI 3.0-3.1%)). There was no difference in the adjusted hospital mortality of patients classified as third sex compared to the other groups. InterpretationPatients classified as third sex composed a small minority of adult ICU patients. This group had a different diagnostic casemix, but similar outcomes, to the groups classified as female or male. Further characterizing a third sex group will require improved processes for recording sex and gender in health records.