16th January 2024

Diagnosis

Although GPA is a rare condition, it should be considered in any patient with atypical or persistent pneumonia. Several classification systems exist but were not intended for diagnostic use; therefore, they have not been included in this section. The main investigations which should be performed as part of confirming a diagnosis are summarised below.

Table 2: Summary of investigations used in diagnosis of GPA, with explanation of findings. Adapted from: Falk, R., Merkel, P. and King Jr, T. (2022) Granulomatosis with polyangiitis and microscopic polyangiitis: Clinical manifestations and diagnosis, UpToDate. Edited by R. Glassock et al. Available at: https://www.uptodate.com/contents/granulomatosis-with-polyangiitis-and-microscopic-polyangiitis-clinical-manifestations-and-diagnosis?search=gpa&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1 (Accessed: January 15, 2023) and Molloy, E. (2022) BMJ Best Practice Granulomatosis with polyangiitis. Available at: https://bestpractice.bmj.com/topics/en-gb/327/pdf/327/Granulomatosis%20with%20polyangiitis.pdf (Accessed: January 15, 2023). 

Depending on the symptoms present, other investigations may be needed e.g., lung function or bronchoscopy may be needed to further explore signs like shortness of breath and haemoptysis, to rule out other conditions such as PE.

Moreover, a positive ANCA result on immunoassay can also occur in other disorders, e.g., IBD, infective endocarditis and malignancy. A careful history and examination are needed when considering GPA as a diagnosis, and if there is clinical suspicion of alternative disease/conditions, these should be excluded with further investigations if needed.