I get horrible bruising like that fairly frequently after having blood taken, as they always struggle to get enough of an amount worth testing! It usually swells too, and can be really painful.
I find it often depends on who is taking the blood, and what sort of needle they use. Because my veins are tiny, I should have a fine needle, but there isn`t always one available.
I get round this by having it taken from the back of my hand, using a butterfly needle, and my GP nearly always takes my blood now.
Kathleen x