About
Measures the active free fraction of thyroxine (free T4). A key test of thyroid function.
Preparation
Beyond these general rules, preparation for some tests and diagnostic procedures may require specific instructions from your treating doctor.
Bruising (hematoma) after a blood test
Blood collection is a routine procedure, but it may sometimes cause bruising at the puncture site.
During venous blood collection both the skin and the vein are punctured. When the needle is removed, blood can leak into the surrounding tissue – especially if the pressure in the vein is high – and a hematoma (bruise) may form.
Contributing factors include the body's physiological and anatomical features: the condition of the veins and vessels, their thickness and elasticity, position and visibility.
How to avoid bruising
- Press firmly on the puncture site for 5–10 minutes.
- Keep the plaster on for at least 30 minutes.
- Avoid straining the arm – don't lift anything heavy for an hour and don't drive for the first 15–20 minutes after the draw. Even minor activity can lead to extensive bruising and swelling around the site.
