A 30 year-old female presents to your office with fatigue, shortness of breath, headaches and palpitations that are progressively getting worse over the last few weeks. On physical examination, you find a woman in mild distress with pallor and tachycardia. Laboratory tests are significant for microcytic anemia, due to iron deficiency anemia. As you evaluate this patient for anemia, one medical student starts talking about Mentzer index. Which of the following is true about this index?
