I don’t know the exact percentage of iron in the blood. But about half of the volume of blood is made up of red blood cells. And red blood cells are basically little bags stuffed with haemoglobin.
Haemoglobin is the oxygen-carrying protein and each haemoglobin molecule has 4 atoms of iron. The iron atoms are actually the bit of haemoglobin that grabs oxygen molecules when the blood is in the lungs; they let it go again when the blood gets to other parts of the body.
So yes – we are a bit magnetic but we are full of a magnetic fluid rather that being a magnetic solid (like a, um, magnet).
And I’m not sure if we are magnetic enough to be picked up by an electromagnet – I suspect not!
I found some answers to the first part of the question on the web, but this it turns out to be quite complicated. As iron levels in the blood can be important for medical diagnoses, I don’t want to give any figures here which could be misleading if a worried patient stumbled on this page.
Iron in metal form is very magnetic because its structure allows the magnetic property (spin) of the atoms to align with one another. This is not the case when the iron is in a compound or for blood where it is bound with the hemoglobin (I’m spelling it the American way) in red blood cells. However each atom still has a tiny magnetic field. These fields are not aligned and tend to cancel one another out, so the blood as a whole is not magnetic in the conventional sense.
Interestingly, the magnetic properties of blood vary according to whether the hemoglobin has latched onto oxygen or not. These changes in turn affect the magnetic resonance of nearby protons, which is what is imaged in an MRI scanner. We use this Blood Oxygenation Level Dependent (BOLD) signal to detect changed in brain activity in our experiments.