Feeling fatigued, weak, or short of breath? This test is the essential first step. The Serum Iron test measures the amount of iron that is currently circulating in your blood. Iron is a non-negotiable component of hemoglobin, which carries oxygen to your entire body. This test is a fundamental tool for diagnosing iron-deficiency anemia, the most common type of anemia. This simple blood test is the starting point for reclaiming your energy. Find out if low iron is what's holding you back.