There are blood disorders of the antibodies...that can thicken the blood when it is cold out. One is Cryoglobulinemia.
Another is MGUS.

People with these disorders have to watch their diet, and not
eat too much fat at one time, which will also thicken the blood.
Getting dehydrated is also serious for these people.

There are over 100 causes of Raynaud's... it is a very common symptom.

I'd have your friend, soak in warm water, with those epsom salts, as this will open up the small blood vessels and improve circulation. The magnesium in there is very very helpful.

Autoimmune diseases, and all sorts of things can cause this.

Epsom salts is one the main remedies we use on the Peripheral Neuropathy forum. It is nothing short of amazing how beneficial these soaks can be!

When this works, it clarifies possible diagnosis as to what is going on and helps the doctor decide what to do.