The Miller criteria is a clinical calculator used for assessing the severity of Pneumocystis pneumonia (PCP) in patients, particularly those with HIV/AIDS. This scoring system is crucial in determining the need for hospitalization and intensive care, as well as guiding treatment decisions. The Miller criteria takes into account factors such as arterial oxygen pressure (PaO2), arterial-alveolar gradient (A-a gradient), and the presence of extrapulmonary disease. Patients with severe PCP according to the Miller criteria may require more aggressive treatment and closer monitoring. The calculator may not be applicable or accurate in patients with co-existing lung diseases or conditions that can affect the PaO2 or A-a gradient.

Miller criteria for PCP severity assessment

# Criteria
 ## Symptoms and signs
A. Dyspnea on exertion with or without cough and sweats
B. Dyspnea on minimal exertion, occasional dyspnea at rest, fever, cough
C. Dyspnea at rest, tachypnea at rest, persistent fever, cough
## Arterial oxygen tension (arterial partial pressure of oxygen) at rest, room air
D. > 11.0 kPa (> 82.5 mmHg)
E. 8.1-11.0 kPa (60.75-82.5 mmHg)
F. < 8.0 kPa (< 60 mmHg)
## Arterial oxygen saturation (SaO2) at rest, room air
G. > 96%
H. 91-96%
I. < 91%
## Chest X-ray
J. Normal or minor perihilar shadowing
K. Diffuse interstitial shadowing
L. Extensive interstitial shadowing with or without diffuse alveolar shadowing

# Conditions
- C or F or I or L
- A and D and G and J
- B or E or H or K
- true