Hemochromatosis: Tests and diagnosis – MayoClinic.com:

“Blood tests
At any stage — even before symptoms appear — doctors can detect iron overload with two blood tests:

Serum transferrin saturation. This test measures the amount of iron bound to a protein (transferrin) that carries iron in your blood. Transferrin saturation values greater than 45 percent are considered too high.
Serum ferritin. This test measures the amount of iron stored in your body. If the results of your serum transferrin saturation test are higher than normal, your doctor will check your serum ferritin. Because a number of infectious and inflammatory conditions other than hereditary hemochromatosis can cause elevated ferritin, both tests are needed to diagnose the disorder. You may need the tests repeated for the most accurate results.”