Hi Manal,
When the Hb is described as 98% HbF it means that 98% of the total hemoglobin is fetal hemoglobin, but it is not a measurement of the total quantity of hemoglobin. The total hemoglobin in this case is actually very low, but what hemoglobin is there is mostly HbF. An analogy would be, suppose you are baking bread and need 4 cups of wheat flour and you discover you only have a pinch of wheat flour but you have half a cup of rye flour. 98% of the flour you have is rye flour. You have flour, but not enough to bake your bread. This is the same thing. Of the hemoglobin that Abdulwahab had, 98 % was HbF, but the total Hb wasn't enough to "bake the bread" of survival.