Elevated haemoglobin levels - should I be concerned?

Hi I just got back from my second blood test. This time I had to go and see a consultant who did a quick check on me. When I had my first blood test my haemoglobin levels were 17.7 and now 6 weeks later they're 17.9. The doctor isn't too concerned as there is no obvious cause for it right now. He's asked me to come back in again in 6 weeks for another blood test. Is this a waste of time or should I be concerned? I've had loads of blood tests in the past (3 years +) and was a donor at one point and he said if there was anything wrong I would have been told then.

Any advice would be appreciated.

Thanks in advance