Hi Zahra,
Do you have electrophoresis tests before and after starting hydroxyurea? This is far more important for determining whether or not any benefit is being derived from hydroxyurea than Hb alone. What is hoped is that the percentage of HbF is rising even if the hemoglobin level is staying in the same range. If hydroxyurea has little or no effect on HbF, there is much less chance of it working, but if there is a transition to more HbF, this is a good sign and shows the intended changes are happening. Hydroxyurea will somewhat suppress the bone marrow, so the amount of bad hemoglobin being produced will drop, while the HbF level will rise. If this occurs but the hemoglobin level doesn't move much, it is still a positive gain, so then physical observations may become more important in deciding whether or not to continue hydroxyurea.
I would also say,it hasn't been long enough to make a determination, as it takes one to two years to see the total effect. Also, since he was sick, this can affect everything, so patience is required.
Hydrate, hydrate, hydrate. All thals should listen to this. Chelators affect the kidneys and liver and you need to stay hydrated at all times, especially when using oral chelators.