The normal development of red blood cells requires a coordinated synthesis of the hemoglobin (Hb) subunits, the ?- and ?-globins in the case of adult hemoglobin (Hb A). Unlike the ?-hemoglobin chains (?-Hb) which are soluble and form homologous tetramers, the free ?-hemoglobin chains (?-Hb) are highly instable, may form precipitates and act as active oxidants.The molecular chaperone of ?-Hb, the « Alpha-Hemoglobin Stabilizing Protein » (AHSP) was reported to specifically bind to ?-Hb to form a stable soluble heterodimer but not to the ?-Hb or to tetrameric Hb A. Hence the role of AHSP could be to prevent free ?-Hb from aggregation until the encounter of other ?, ? or ? chains. In the red blood cell of ?-thalassemic patients, AHSP acts as a scavenger against the pool of free ?-chain but may be overwhelmed by a defective production or level of availability of ?-like chains. The free ?-chain pool may thus reflect the severity of a ?-thalassemia syndrome.rnCurrently, the diagnosis of ?-thalassemia is still based on the hematological parameters of the patients and the molecular diagnosis is obtained by PCR techniques to identify point mutations for most at-risk populations. The severity of the ?-thalassemia also depends on the nature of the mutation. More generally one may need to consider the overall imbalance between the ? and ? family of globin chains. Currently, the only technique to quantify the relative excess of free ?-Hb is to carry out globin biosynthesis in vitro in the presence of a radioactive amino-acid. Therefore, there is a need for a method for easily diagnosing and/or staging a hemoglobin-related disorder without using molecular or radioactive technique. rnrnThus, the invention relates to a method for diagnosing and/or staging a hemoglobin-related disorder, such as ?-thalassemias, in a subject in need thereof. The invention also relates a method for monitoring a treatment against said hemoglobin-related disorder in a subject in need thereof.rnrnScientific publication(s):rnAm J Hematol., 2017 Oct, Vasseur C. et al., Elevated soluble ?-hemoglobin pool in sickle cell anemia, doi: 10.1002/ajh.24835rnBJH, 2017 Apr, Vasseur C. et al., Red blood cells free ?-hemoglobin pool: a biomarker to monitor the ?-thalassemia intermedia variability. The ALPHAPOOL StudyrnAm J Hematol., 2011 Feb, Vasseur C. et al., Evaluation of the free ?-hemoglobin pool in red blood cells: a new test providing a scale of ?-thalassemia severity, doi: 10.1002/ajh.21918