Les prises de sang sont-elles payantes en France ?

Hello, I have inherited primary trombophilia. I should do regular check ups on yearly basis. I want to ask how is a process in Belgium. Do I need firstly visit a general doctor and ask general doctor to take a blood and to send to laboratory? I tried to find hematologist but I didnt found, I just found a blood testing centres. Thank you.

I just did a 24 hour urine collection with blood sample. eGFR is 125, I drank 2.4L of water in the 24 hour period and had 1.625L of urine output. But the thing is my creatinine was 169 mL/min/1.73m2 when normal range according to lab is 88-135. Also my urea was 1124mg/dL or 18g/24h when normal range according to lab is 1710-3570mg/dL or 25.8-42.6g/24h. I'm in a bit of panic as these seem very low in comparison to normal range and I'm only seeing my urologist in a month from now. Please help me out explaining this so I can calm down a bit. Thanks in advance.