This study aims to investigate the impacts of abnormally elevated PTH levels on clinical outcomes among critically ill patients with vitamin D depletion.

This study is a secondary analysis of data from a previous multicentre, prospective, observational cohort study (REC No: 201805087RINB) examining vitamin D deficiency prevalence and outcomes in critical care. From the previously enrolled 651 critically ill patients admitted to medical and surgical intensive care units (ICUs), those enrolled within 48 hours of admission are analyzed. Vitamin D depletion is defined as a serum 25-hydroxyvitamin D (25(OH)D) level <30 ng/mL. Patients are categorized as PTH non-responders (PTH levels of 15-68.3 pg/mL) or PTH responders (PTH levels > 68.3 pg/mL). The primary endpoints include the rate of survival to day 28 and the rate of survival to hospital discharge. Secondary endpoints include the length of ICU stay at day 28 and day 90, Acute Physiology and Chronic Health Evaluation (APACHE) II score, Sequential Organ Failure Assessment (SOFA) score, and blood clinical laboratory variables.

Inclusion criteria:

1. Critically ill patients within 48 hours of ICU admission

Exclusion criteria:

1. Less than 20 years old
2. Severe malnutrition (BMI<18kg/m2)
3. Severe anemia (hemoglobin concentration <7g/dL)
4. Receiving high-dose vitamin D treatment (> 3000 IU/day) within four weeks
5. Have been admitted to the ICU within three months
6. Suffering from diseases that affect vitamin D concentration, calcium metabolism or bone metabolism (for example: parathyroid disease, rickets, chirtosis, and severe cirrhosis [Child C])
7. Patients and family members who do not speak the native language

Critically ill patient