Why does my son have thick blood and his hands and legs turn purple and blotchy?

My 22 yr old son has really thick blood and seemingly circulation problems as well. His legs and arms and hands turn purple and blotchy when its slightly cold and when you push on his skin it goes white and stays that way for a very long time. He drinks a lot of water so I dont believe he has dehydration issues. I have a cardio check and we checked his triglyerceride and cholesterol levels but he could barely put a drop of blood on the test strip. I have thick blood too but its because i have hyperlipidemia with real high triglyceride levels. His triglycerides are 87 and his cholesterol registered below 100. I was reading about Hughes Syndrome. Do I need to be concerned here? He complains lately that his thumb keeps going numb too. Please help me, if this is serious I need to know.