In general, testosterone therapy in older men tends to cause an increase in the oxygen-carrying capacity (hemoglobin) of the blood. This can bring improved energy levels and a decrease in fatigue in some men. In others, however, the increase can be great enough to cause concern. Just to be safe, the hemoglobin level should be measured before and during therapy for a period of time. <br> <br> When injectable and implantable testosterone were the only therapy choices, this large increase in hemoglobin occurred more often. New delivery forms such as patches or gels provide a more uniform testosterone level from day to day, which may help prevent this change from occurring.