Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services for:
A seizure, fainting, severe confusion, or difficulty waking
Trouble breathing or chest pain
No urine or a major sudden reduction in urine
Severe weakness, collapse, or uncontrolled bleeding
Signs of a serious infection while receiving complement-blocking treatment, such as fever with severe headache, stiff neck, rash, or marked drowsiness
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Seek urgent same-day medical care for bloody diarrhea, especially when it is accompanied by unusual tiredness, pale skin, bruising, swelling, or reduced urination.
HUS can develop after the diarrhea starts to settle.
3
Does any of this apply?
Book an appointment
Routine follow-up is appropriate for blood pressure checks, kidney tests, medication monitoring, and discussion of genetic results when you otherwise feel stable.
The article also says
If you have previously had complement-mediated HUS, follow your specialist’s plan for new vomiting, diarrhea, infection symptoms, dark urine, bruising, or reduced urine output.
Every sign above is quoted from the sofidex article on Hemolytic-uremic syndrome. If you are not sure, err upward — it is always reasonable to be checked.