High RBC are usually due to dehydration or low oxygen as in high altitudes and in lung disorders such as asthma. Congenital heart disease, some kidney problems and polycythemia vera are the other causes of increased RBC.
Hypothyroidism usually causes anemia. So, if RBC is high then other blood parameters such as RDW, MCV, MCH, MCHC should be done. Please consult your doctor regarding this. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.