It can quite stressful for a man who has finally gotten on HRT, feels better and then finds out that his hemoglobin is high. Of course, he can always lower his testosterone dosage to try to solve the problem, but this may not be a solution that either doctor or patient want to pursue. Many men have found that their erectile dysfunction is greatly helped and/or morning erections and libido have returned. The last thing they want to do is lower their dose.
So why even worry about a high hemoglobin or RBC count? What’s a few extra red blood cells anyway?
Unfortunately, high hemoglobin (or RBCs) is a risk factor for ischemic stroke, i.e. the standard kind of stroke where there is a loss of blood supply to tissues such that permanent damage is usually incurred.  Of course, a stroke can be a life-changing (or life-ending) event and should be avoided at all costs. There is also a longer term risk as well: elevated hemoglobin could lead to unhealthy iron store levels which is associated with heart disease and dementia. Iron in tissues can lead to oxidative damage.
Just look at what some recent studies have concluded:
“Low and high hemoglobin concentrations in older persons are associated with a lower level of cognitive function in old age, particularly in semantic memory and perceptual speed.” 
“In older persons without dementia, both lower and higher hemoglobin levels are associated with an increased hazard for developing AD [Alzheimers Disease] and more rapid cognitive decline.” 
NOTE: There are several standard ways to measure red blood cells: hematocrit, hemoglobin and RBC (red blood cell count). All of these are related and doctors will usually look at two or more. Hematocrit is the volume measurement, i.e. the percentage of blood that is taken up by the red blood cells. Hemoglobin, on the other hand, is a density or concentration measurement and is expressed in grams per liter or deciliter. (Hemoglobin is, if you will recall from your high school biology, the iron-based protein that transports oxygen.) RBC is a simple count and is usually expressed as the number of million red blood cells that you have per microliter.
1. Give Blood. This is a time-proven technique for men on testosterone therapy to lower their hemoglobin levels. And you are helping out someone else while you’re doing it! Look at what one of our senior posters wrote about this:
Notice that he dropped his hemoglobin by about 12%. Not bad for about an hour of time, eh?
2. Lower Your TRT Dose. If you have high hemoglobin or hematocrit from testosterone therapy, then your doctor may require you to lower your dose. This is not always a bad thing as some men are actually taking more than they actually need, which can lead to side effects in both the long and short term. See my page on The Side Effects of Testosterone Therapy for more information.
3. Drink Water. It is important to remember that hemoglobin is very dependent on your hydration levels. If you were dehydrated when you had your blood draw, this could have made things worse. If you think you were dehydrated, discuss a retest with your doctor.
4. Hyperthyroidism. Hypothyroidism can lower your RBC counts and hyperthyroidism can raise them some.  If you haven’t checked your thyroid function lately, this might be wise. And don’t forget to get a full workup, including antibodies, if you can afford it. See my page on Testosterone and the Thyroid for more details.
5. Transdermal (Topical) Testosterone? One research summary stated that topical lead, in general, to lowered levels versus intramuscular injections:
“Intramuscular testosterone is the only form that significantly increases hematocrit above normal levels. However, it does so strongly, with up to a 6% change from baseline. The runner-up is testosterone gel, with an average increase of 2.5% over baseline levels.” 
Therefore, if you are on intramuscular injections and struggling with high hematocrit or hemoglobin, going on topicals may help a little. Discuss with your physician. NOTE: A cheap alternative is Compounded Testosterone Creams and Gels.
6. Avoid Red Meats. It is interesting because one of the criticisms that meat eaters level against vegetarians is that plant foods have many “anti-nutrients” that can slow down or bind with minerals such as iron. For example, organizations like Weston Price love to castigate vegetarians for their phytic acid consumption. Phytic acid is present in plant foods and binds to iron, magnesium, phosphorous and calcium. It can, if overconsumed, lead to mineral deficiences. However, Dr. Bernard points out that usually it is likely very health protective for most people, because these minerals, as in the case of zinc and iron, have been found to be neurotoxic at even relatively low levels of tissue accumulation. Research has also shown that too much iron also contributes to heart disease and there may be a link to colon cancer as well. 
So avoiding red meats, which are high in heme iron, stands a good chance of lowering your hemoglobin scores and protecting your long term health unless some other preventative action is taken (such as giving blood). For other cautions about meat consumption, especially red meat, seemy link on The Risks of Meat Consumption.
As a verification, one study of vegetarians and non-vegetarians found that females had significantly lower hemoglobin levels. Males had lower levels but it may not have been statistically significant.  However, another study was more definitive and concluded: “It was found that hemoglobin, hematocrit, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, white blood cells, neutrophils, serum ferritin and serum vitamin B12 in vegetarian were significantly lower than control subjects.”  The ferritin is a key measure, by the way, because it indicates that tissue levels of iron are lower and thus will likely cause less permanent damage. (This study did show that some vegetarians were iron deficient it should be noted.)
7. Fix Sleep Apnea. One of our senior posters was told that sleep apnea tends to thicken the blood in this Peak Testosterone Forum thread. And, sure enough, the studies confirm this as well.  So, if your hematocrit, hemoglobin or RBC’s are running high, think about getting tested for sleep apnea. A recent study commented that “one possible explanation is that repeated episodes of nocturnal hypoxia lead to a hypercoagulable state that predisposes patients to thrombotic events. There is evidence supporting a wide array of hematological changes that affect hemostasis (eg, increased hematocrit, blood viscosity, platelet activation, clotting factors and decreased fibrinolytic activity).”
8. Inflammation. Hepcidin activity can be governed by inflammation. Checking for infections, CRP levels, etc. and then treating the underlying cause may help. 
1) Eur Neurol, 1996, 36(2):85-8, “A positive relation between high hemoglobin values and the risk of ischemic stroke. Progetto 3A Investigators”
2) Neuroepidemiology, 2008 December, 32(1): 40 46, “”Relation of Hemoglobin to Level of Cognitive Function in Older Persons”
3) Neurology, 2011 Jul 19, 77(3):219-26, “Hemoglobin level in older persons and incident Alzheimer disease: prospective cohort analysis”
5) International Journal of Natural and Applied Sciences Vol. 2 (3) 2006: pp. 174-177, “Comparative study of the hemoglobin concentration of vegetarian and non-vegetarian subjects in Ogun state, Nigeria”
6) J Med Assoc Thai, 1999 Mar, 82(3):304-11, “Hematological parameters, ferritin and vitamin B12 in vegetarians”
7) World J Gastroenterol, 2006 September 21, 12(35): 5644-5650, “Hemoglobin induces colon cancer cell proliferation by release of reactive oxygen species”
8) Iran J Ped Hematol Oncol, 2013; 3(2):73 77, “Effect of Thyroid Dysfunctions on Blood Cell Count and Red Blood Cell Indice”
10) Can Respir J. 2011 Nov-Dec; 18(6): 338 348, “Coagulability in obstructive sleep apnea”