When I was first diagnosed with pmr my hemoglobin level was 11.5 gm/dl., slightly below the normal range. I usually average a level somewhere between 12 and 13 gm/dl. After starting prednisone my hgb returned to my normal level.
I have experienced a few relapses when my crp significantly elevated and my hgb level decreased. Increasing prednisone during flares lowered my crp and consequently hgb increased.
pmr seems to affect us all differently but in my case active inflammation lowers my hgb..
I would say that pmr can cause your hgb level to drop but "20 points" needs clarification.