The PRIEST score for COVID-19 clinical severity helps evaluate a patient’s risk of adverse outcomes by considering several key health indicators and personal characteristics. For calculation, each aspect is scored based on predefined criteria, reflecting its contribution to clinical severity assessment. Here's how each factor is evaluated:

- Sex: Female gets 0 points, Male gets 1.
- Age:
  - 16-49 years: 0
  - 50-65 years: 2
  - 66-80 years: 3
  - Over 80 years: 4
- Respiratory Rate (breaths per minute):
  - Less than 9: 3
  - Between 9-11: 1
  - Between 12-20: 0
  - Between 21-24: 2
  - More than 24: 3
- Oxygen Saturation:
  - More than 95%: 0
  - Between 94-95%: 1
  - Between 92-93%: 2
  - Less than 92%: 3
- Heart Rate (beats per minute):
  - Less than 41: 3
  - Between 41-50: 1
  - Between 51-90: 0
  - Between 91-110: 1
  - Between 111-130: 2
  - More than 130: 3
- Systolic Blood Pressure (mmHg):
  - Less than 91: 3
  - Between 91-100: 2
  - Between 101-110: 1
  - Between 111-219: 0
  - More than 219: 3
- Temperature:
  - Below 35.1°C (95.18°F): 3
  - Between 35.1-36.0°C (95.18-96.8°F): 1
  - Between 36.1-38.0°C (96.8-100.4°F): 0
  - Between 38.1-39.0°C (100.4-102.2°F): 1
  - Above 39.0°C (102.2°F): 2
- Alertness:
  - Alert: 0
  - Confused/not alert: 3
- Inspired Oxygen:
  - Air: 0
  - Supplemental oxygen: 2
- Performance Status:
  - Unrestricted normal activity: 0
  - Limited strenuous activity/light activity: 1
  - Limited activity/self-care: 2
  - Limited self-care: 3
  - Bed/chair bound, no self-care: 4

The total PRIEST score is derived by summing the scores from these parameters, yielding a result between 0 and 29. This score helps predict the risk of a 30-day adverse outcome, with higher scores suggesting increased risk. The interpretation of the total score is:

- A score of 0-1 corresponds to a 1% risk.
- A score of 2-3 corresponds to a 2% risk.
- A score of 4 suggests a 3% risk.
- Scores increase in risk as follows: 5 (9%), 6 (15%), 7 (18%), 8 (22%), 9 (26%), 10 (29%), 11 (34%), 12 (38%), 13 (46%), 14 (47%), 15 (49%), 16 (55%).
- Scores from 17 to 25 range from 59% to 88% risk.
- A score of 26 or higher indicates over a 99% risk.

The PRIEST (Pandemic Respiratory Infection Emergency System Triage) score is a clinical calculator specifically designed for patients with suspected COVID-19. This scoring system is used to predict the risk of hospital admission and severe outcomes in patients presenting to the emergency department with suspected COVID-19 symptoms. 

The PRIEST score takes into account factors such as age, sex, comorbidities, vital signs, and oxygen saturation levels. The higher the score, the higher the risk of hospital admission and severe outcomes, including death. 

The clinical utility of the PRIEST score is to aid in the triage of patients, helping healthcare providers to identify those who are at higher risk and may require more intensive care or monitoring. 

There are no specific exclusion criteria for the use of the PRIEST score, but it should be noted that it is specifically designed for use in patients with suspected COVID-19 and may not be applicable or accurate in patients with other conditions.