OBJECTIVES: International Classification of Diseases-10 (ICD-10) surrogates of the modified frailty index (mFI) were defined in recent research. We investigated the prevalence of these ICD-10 codes and their association with hospital referral in the elderly German population.

METHODS: We included adults aged ≥65 years followed in 1,284 general practices in Germany between 2010 and 2021. There were 11 ICD-10 surrogates of the mFI, including 54 diagnoses. Hospital referral was determined in the 12 months following ICD-10 surrogate assessment. Cox regression models were adjusted for age and sex.

RESULTS: 1,406,038 patients were included (mean age 77.0 years (SD=7.9); 56% women). Prevalences of ICD-10 surrogates of the mFI ranged between 3% (“history of transient ischemic attack or stroke without neurological deficit”) and 68% (“history of hypertension requiring medication”). 24%, 37%, and 23% of patients had 1, 2-3, and >3 ICD-10 surrogates of the mFI, respectively. There was a positive and linear association between the number of ICD-10 surrogates and incident 12-month hospital referral (HR [95%CI]; 1 surrogate: 1.37 [1.31-1.42]; 2-3 surrogates: 2.00 [1.93-2.08]; >3 surrogates: 3.32 [3.19-3.44]; reference: no surrogate).

CONCLUSIONS: ICD-10 surrogates of the mFI predicted incident 12-month hospital referral and may be used to identify outpatients most at risk in Germany.