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
Go to an emergency department promptly if there is an obvious deformity, an open wound, severe swelling, or severe pain after a significant injury.
Call emergency services if the hand becomes cold, pale, or blue, or if the child cannot move or feel the fingers normally.
These are not typical signs of radial head subluxation and may mean blood flow or nerves are affected.
And for anyone, someone who:
has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
has had a seizure that will not stop, or does not wake up afterwards
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 is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
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 same-day medical care if a young child suddenly stops using an arm, even if there is no swelling and the suspected pull seemed minor.
Prompt examination can confirm whether repositioning is appropriate and check for other injuries.
Get urgent medical advice if:
The child still will not use the arm after treatment
Pain, swelling, or bruising is increasing
The elbow becomes red, hot, or swollen
The child has a fever or appears unwell
Symptoms followed a fall or direct blow
Similar episodes keep happening or occur in an older child
And for anyone, someone who:
has a fever with a stiff neck, a rash that does not fade under pressure, or severe headache
is vomiting and cannot keep fluids down
has a new severe headache unlike any they have had before
Every sign above is quoted from the sofidex article on Radial head subluxation. If you are not sure, err upward — it is always reasonable to be checked.