A PNH diagnosis is confirmed by a specialised blood test called flow cytometry. Usually, several other tests are performed during the diagnostic process to rule out complications of PNH and assess its severity. These may include a bone marrow biopsy, blood tests, x-rays, CT scans, an ultrasound and other specimen tests ie. urine.

PNH can affect anyone of any age, but is most commonly diagnosed in young adults in their 20s or 30s. Usually, symptoms appear gradually are a non-specific (e.g. tiredness, abdominal/muscular pain, headaches) so it can take years for a PNH to be diagnosed.

Symptoms and severity of the disease vary widely, allowing some patients minimal disruption to their daily lives while others are severely limited in their ability to work, socialise and undertake simple physical activities such as light housework or walking.