Introduction
The impact of population aging on health expenditure is inevitable. Aging affects health expenditure by causing changes in people’s health status and the demand for health care services. From 2020 to 2050, the number of people over 65 years of age in Iran will increase from about 5 million to 20 million people, and one of the fastest demographic changes will occur in the country [2, 3]. Although old age and demographic variables are not the only factors affecting changes in health expenditures, it is important to examine them from different aspects. The objectives of this study include:
1. To assess and compare the rate of hospital admission by age and sex groups;
2. To compare the rate of admission to public and private hospitals across different age groups;
3. To examine and compare age-related and gender-related differences in hospital costs;
4. To determine and compare the average hospital costs of elderly and non-elderly patients based on the type of services received;
5. To analyze the relationship between patients' age and the hospital admission rate, length of stay, and hospital costs.

Methods
This is a quantitative, descriptive-analytical study with a cross-sectional design that was conducted on hospital documents related to the insurance claims of 41 million people insured by the Iran Health Insurance Organization. The hospitalization documents of patients who had visited 956 hospitals in Iran from March 20, 2020 to March 20, 2021, and had a medical record were included. The dependent variables were hospital admission rate, length of stay in hospital, and hospital costs. The hospital admission rate was obtained by dividing the number of admissions by the number of covered population in each age and sex group. In this study, the word “cost” indicates the total payments to hospitals, including the insurer’s share, the patient’s share, and government subsidies. The average hospital cost per patient was calculated by dividing the total cost in age and gender groups by the number of patients in each group. Descriptive variables included the age and gender of patients, the ownership of hospitals, and the type of patients’ medical records. The Mann-Whitney test was used to compare the average cost of each person in two groups of men and women and two groups of elderly and non-elderly. Spearman’s correlation test was used to examine the relationship between response variables and age. The data were analyzed in SPSS software, considering the significance level of P<0.05. Costs are reported in Iranian Rials. At the time of the study in 2020, the average exchange rate of the US dollar was equal to 42173.87 Iranian Rials.

Results
The total number of hospital admissions was 3,807,953, and the total hospital cost in 2020 was 2,891,030 million Rials. The rate of hospital admission was 26% in the elderly and 7% in the non-elderly. The average length of stay was 2.2 days for the non-elderly and 1.3 days for the elderly. The rate of hospital admission was 9.8% in women and 8.5% in men. The hospital admission rate for women under the age of 60 was 8%, and for men under the age of 60 was 6%. In the elderly, the hospital admission rate was higher in old men than in old women (27% vs. 24 %) (Figure.1a).
The highest average hospital cost (47 million Rials) was related to the age group of 70-75 years. The average cost for each non-elderly patient is 28 million Rials, while for each elderly patient, it was 45 million Rials. The average cost per patient was 34,832 thousand Rials for men and 31,970 thousand Rials for women (P=0.010). Men had a longer stay in hospital than women (2.9 days vs. 2.6 days; P<0.001). Men at the age of 70-79 had the highest average hospital costs, which decreased with the increase in age. There was a constant increase in average hospital costs in women from 10 to 90 years of age (Figure.1b).



The most expensive services that people in all age groups received in hospitals were room, medicine, and operating services. The cost of receiving these services in elderly patients with the observed average difference of 3,929 (P<0.001) for room, 2,431 (P<0.001) for medicine,and 5,609 (P<0.001) for operating services was more than that of non-elderly patients. The average cost of operation, room, medicine, and medical supplies in the elderly was about 1.5 times higher than in non-elderly people. Hospitals’ least common and expensive services were radiotherapy, dialysis, and prosthetics. The average cost of non-elderly people for chemotherapy, ambulance, and blood transfusion services was significantly higher than that of elderly people. In other services, the elderly had a higher average cost. The average cost of surgery, hospitalization, medicine, and medical consumables in the elderly was about 1.5 times higher than in non-elderly people. There was a positive and significant relationship between the hospital admission rate and the age of the patients (r=0.879, P<0.001). Also, as the age of patients increased, the length of stay in the hospital increased significantly (r=0.582, P<0.001). The relationship between the patient’s age and the average hospital cost was also positive and significant (r=0.582, P=0.006).

Conclusion
The hospital admission rate in the elderly in Iran is 3.7 times that of non-elderly people. Old men have a higher admission rate than women, while in non-elderly people, the admission rate of women is higher. The length of stay and the average cost of men patients are higher than those of women patients. The average cost of each elderly patient is 1.6 times that of each non-elderly patient. Many of the hospital services are more expensive for elderly patients than for non-elderly patients.

Ethical Considerations

Compliance with ethical guidelines
This study was approved by the ethics committee of Tehran University of Medical Sciences, School of Health (Code: IR.TUMS.SPH.REC.1400.290).

Funding
This study was extracted from the PhD thesis of Mahya Razimoghadam. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Authors' contributions
Conceptualization and design: Mahya Razimoghadam; data collection: Mahya Razimoghadam, Rajabali Daroudi, Zahra Shahali, Aliakbar Fazaeli; data analysis: Mehdi Yaseri, Mahya Razimoghadam, Rajabali Daroudi. All authors contributed to draft preparation and approved the final version of the manuscript.

Conflicts of interest
The authors declare no conflict of interest.

Acknowledgments
The authors would like to thank the National Center for Health Insurance Research for facilitating access to the data.



References