• This is a single-site retrospective electronic chart review of Cooper Health System Inpatients and Outpatients from 2008 through 2023 aged eighteen years or older. This review is designed as an emulation of a randomized clinical trial with a nonrandomized database.
• The primary objectives are to compare healthcare costs and healthcare utilization between subjects who have corrected low vitamin D levels and those without corrected low vitamin D levels.

• The purpose of the study is to characterize healthcare costs and healthcare utilization in subjects with corrected low (<40 ng/ml) 25-OH vitamin D levels compared to subjects with uncorrected low 25-OH vitamin D levels during a three-year period.
• The primary objective of this study is to determine whether ten healthcare costs are lower and ten healthcare utilization parameters occur less frequently in patients with corrected low vitamin D levels compared to patients with uncorrected low vitamin D levels in Cooper outpatients and inpatients.

The costs are:

1. total billed costs for any reason;
2. total billed costs for hospitalizations;
3. total billed costs for ICU admissions;
4. total billed costs for emergency room visits;
5. total billed costs for all other outpatient services;
6. total billed costs for urgent care visits;
7. total billed costs for primary care physician (PCP) services;
8. total billed costs for nurse practitioner (NP) services;
9. total billed costs for all other professional services;
10. total billed costs for medical pharmacy services and products.

The parameters are:

1. number of hospitalizations for any reason;

2. number of ICU admissions for any reason;

3. number of emergency room visits for any reason;

4. all other outpatient services for any reason;

5. number of urgent care visits for any reason;

6. number of primary care physician visits for any reason;

7. number of nurse practitioner visits for any reason;

8. all other professional services for any reason;

9. number of medical pharmacy services for any reason;

10. number of free-standing prescriptions for any reason.

    • The secondary objective is to determine the effect of sufficient vitamin D levels (≥ 40 ng/ml) in subjects not requiring a prior correction on the ten healthcare costs parameters and the ten healthcare utilization parameters listed in the primary objective above.

Inclusion Criteria:

• Any patient with at least one 25-OH vitamin D test result. Patients with one test result will remain in the limited dataset for potential future research.
• Any patient with a 25-OH vitamin D level(s) always lower than 40 ng/ml (low level) with subsequent level(s) in the 40 ng/ml to 100 ng/ml range. The 40 ng/ml to 100 ng/ml range is maintained for three years. This corrected group is labeled as the Treatment Group.
• Any patient with a 25-OH vitamin D level always lower than 40 ng/ml with maintenance of that lower than 40 ng/ml level for 3 years. This uncorrected group is labeled as Control Group A.
• Any patient who has an uninterrupted 25-OH vitamin D level greater than or equal 40 ng/ml and less than or equal to 100 ng/ml (sufficient level) for a continuous 3-year period. Prior to the 3-year period there were no levels lower than 40ng/ml or higher than 100 ng/ml. This vitamin D3 sufficient group is labeled as Control Group B.

Exclusion Criteria:

• Any patient with only one 25-OH vitamin D3 test result or any patient who cannot be included in the Treatment Group, Control Group A, or Control Group B is excluded.

The investigators anticipate reviewing records from thousands of patients in order to identify enough patients that meet the eligibility criteria. Investigators will enroll at a minimum 3,000 patients in the Treatment Group and at a minimum 3,000 patients in Control Group A regarding the primary objective. In regard to the secondary objective, the investigators will enroll as many as available for Control Group B.