Study design
This study had a retrospective design and used anonymized data from medical records of patients who used the AHHC medical service from November 1, 2019, to November 31, 2020. The study design was reviewed and approved by the Research Ethics Committee of the University of Tsukuba (approval number: 1527).
Telephone triage system in Tokyo, Japan
A well-used telephone triage protocol developed by the Fire and Disaster Management Agency functions as follows: when a patient calls an emergency telephone consultation service, an operator classifies the patient into one of the five categories (red, orange, yellow, green, or white) based on a telephone triage protocol [5, 12, 13]. The protocols are divided into two categories: one for patients aged < 16 years and the other for those aged ≥16 years.
AHHC medical service
We used a private AHHC medical service in Tokyo, established by Fast Doctor Ltd. (Shinjuku, Tokyo, Japan) in 2016, which sends doctors directly to the residence of patients who need a hospital visit. The company operates 7 days a week outside of regular hospital visiting hours (18:00 to 06:00 on weekdays and Saturdays and 24 h on Sundays and holidays).
When a patient calls the AHHC service, operators (trained telephone triage nurses) perform the telephone triage using the telephone triage protocol. The operators determine the following: whether the patient is to remain at home (white), whether an AHHC doctor’s visit to the patient’s residence is needed (orange and yellow), or whether they need an ambulance (red). The operators call an ambulance for patients triaged as red and opt to provide the patient with information about nearby clinics or a primary hospital for patients triaged as green. The trained telephone triage nurses can consult a doctor beside the AHHC medical service call center.
After the AHHC medical service doctors conduct home visits for patients, these doctors classify patients into three categories: grade 1 (can be treated using over-the-counter medications), grade 2 (require a hospital or clinic visit), or grade 3 (require ambulance transportation) [14,15,16].
The doctors affiliated to the AHHC medical service are specialized attending doctors working at a university hospital and aged approximately 35 years. The telephone triage nurses are trained to use the telephone triage protocol in the AHHC medical service.
Figure 1 shows a correspondence table describing telephone triage and the grades assessed by AHHC doctors. Patients who were initially classified as orange and yellow and subsequently classified as grade 2 by AHHC doctors formed the appropriately triaged group. Patients initially classified as orange and yellow and subsequently as grade 3 by AHHC doctors formed the undertriaged group.
Study participants
We included all patients who had used the AHHC medical services between November 1, 2019, and November 31, 2020, and excluded those with missing records of age, sex, telephone triage categories, or doctor grade assessments after consultations.
Data source
The study used anonymized data from medical records of patients using the AHHC medical service (Fast Doctor Ltd.).
Data on the following variables of patients were extracted from medical records: sex, age, comorbidities (hypertension, diabetes mellitus, hyperlipidemia, gout, chronic lung disease, heart failure, liver disease, cerebral infarction, cancer, and dementia), telephone triage categories, protocols, doctor assessments after consultations, vital signs, and time from patients’ phone call to doctors’ consultations.
Statistical analyses
First, we compared baseline characteristics between the appropriately triaged and undertriaged groups. Pearson’s chi-square test or Fisher’s exact test was performed to compare categorical variables (age categories [0–15, 16–64, 65–74, and > 75] years, sex, comorbidities, telephone triage categories, protocols, and doctor assessments), and Student’s t-test or the Wilcoxon-Mann-Whitney test was performed to compare continuous variables (age, vital signs, and time from telephone triage to patient consultation), as appropriate. Second, we conducted a multivariable logistic regression analysis to identify factors associated with undertriage. Third, we conducted sensitivity analyses to exclude patients aged 0–15 years because the protocol used for these patients is different from that used for patients aged > 15 years. All statistical analyses were performed using JMP 16.0 statistical software (SAS Institute, Cary, NC, USA). The significance threshold was set at P of < 0.05.