@simrin-- There are numerous test that measure levels of different elements in the blood. The cbc blood test is one of the most common but it doesn't measure iron levels. The cbc measures red and white blood cell count and hemoglobin among other things. For iron count however, the doctors had probably used a ferritin test for your sister. The blood chemistry lab must have found her iron levels to be less than 11 nanograms to declare her as iron deficient.