The calculator in question is the ACR/EULAR (American College of Rheumatology/European League Against Rheumatism) Classification Criteria for Granulomatosis with Polyangiitis (GPA). This scoring system is used in the clinical setting to help diagnose patients suspected of having GPA, a rare form of vasculitis that affects small- to medium-sized blood vessels.

The ACR/EULAR criteria for GPA are applicable to patients presenting with symptoms suggestive of vasculitis, such as sinusitis, nasal or oral inflammation, lung nodules, or kidney disease. The criteria include a combination of clinical, laboratory, and histopathological findings, and a score is calculated based on the presence and severity of these findings. 

The clinical utility of this calculator is to aid in the diagnosis of GPA, which can be challenging due to its rarity and the wide range of symptoms it can present. Early and accurate diagnosis is crucial for initiating appropriate treatment and improving patient outcomes.

There are no specific exclusion criteria for the use of the ACR/EULAR GPA criteria. However, it should be noted that these criteria are intended for classification purposes in clinical research and not as the sole method for diagnosing GPA in clinical practice. They should be used in conjunction with other clinical and laboratory findings,

ACR/EULAR classification criteria for granulomatosis with polyangiitis

# Criteria
 # Entry criteria
A. Evidence of small- or medium-vessel vasculitis on imaging (+20)
B. Alternative diagnoses mimicking vasculitis are excluded (+20)
# Clinical criteria
C. Nasal involvement: bloody discharge, ulcers, crusting, congestion, blockage, or septal defect/perforation (+3)
D. Cartilaginous involvement: inflammation of ear or nose cartilage, hoarse voice or stridor, endobronchial involvement, or saddle nose deformity (+2)
E. Conductive or sensorineural hearing loss (+1)
# Laboratory, imaging, and biopsy criteria
F. Positive test for cytoplasmic antineutrophil cytoplasmic antibodies or anti-proteinase 3 antibodies (+5)
G. Pulmonary nodules, mass, or cavitation on chest imaging (+2)
H. Granuloma, extravascular granulomatous inflammation, or giant cells on biopsy (+2)
I. Inflammation, consolidation, or effusion of the nasal/paranasal sinuses, or mastoiditis on imaging (+1)
J. Pauci-immune glomerulonephritis on biopsy (+1)
K. Positive test for perinuclear antineutrophil cytoplasmic antibodies or anti-myeloperoxidase antibodies (-1)
L. Blood eosinophil count >= 1×10**9/L (-4)

# Conditions
- score >= 45
- true
- score == 0

2022 American College of Rheumatology / European Alliance of Associations for Rheumatology classification criteria for granulomatosis with polyangiitis.