The normal range for Hemoglobin is 13-17g/dl for male and 12-15 g/dl for female. However recent update in WHO diagnostic criteria for Polycythemia Vera
has Hemoglobin cut-off of 16.5, which has mild overlap with normal range.
This is because, the concept of disease etiology has undergone sea change with the newer highlights on genetic mutations and it is found that few people who otherwise have high normal hemoglobin level can have the genetic mutations and thus develops full blown polycythemia vera, as time flies by. Therefore, if someone have high normal hemoglobin, even though it falls well within normal range, the physicians should be alert of possibility of polycythemia vera and should prescribe for bone marrow studies and genetic studies, which are essential for diagnosis of polycythemia vera. (sole increase in Hemoglobin level above 16.5 gm/dl is not sufficient for diagnosis ). This helps in starting patients with preventive measures, so that life threatening complications of polycythemia vera, like stroke
or AMI, can be prevented. Hope it helps and clarifies your doubts