Excess blood, or more precisely an abnormally high concentration of red blood cells, is reduced through a straightforward procedure called therapeutic phlebotomy: a controlled removal of blood that works much like a blood donation. The target is typically a hematocrit (the percentage of your blood made up of red cells) below 45% for men and below 42% for women. How you get there, and how often you need to repeat it, depends on what’s causing the excess in the first place.
What “Excess Blood” Actually Means
Your body doesn’t literally produce too much blood volume in most cases. What happens is that the proportion of red blood cells climbs too high relative to the liquid plasma they float in. A hematocrit test measures this ratio. When red blood cells make up too large a share, blood becomes thicker and stickier, which raises the risk of clots forming in veins or arteries.
Doctors generally flag a concern when hemoglobin rises above 16.5 g/dL in women or 18.5 g/dL in men. But before assuming something is wrong with your bone marrow, it’s worth ruling out a simpler explanation: dehydration. Severe dehydration shrinks your plasma volume, which artificially inflates your hematocrit on a blood test. Drinking adequate fluids and retesting can sometimes resolve what looks like a red blood cell problem.
Therapeutic Phlebotomy: The Primary Treatment
Phlebotomy is the fastest and most direct way to bring red blood cell levels down. It looks and feels almost identical to donating blood. A needle goes into a vein in your arm, and a set amount of blood drains into a collection bag over 15 to 30 minutes. The difference is the frequency and the medical goal behind it.
During the initial phase, 250 to 500 mL of blood is typically removed every day or every other day until hematocrit drops below 45%. For older adults or anyone with heart disease, smaller draws of 200 to 300 mL twice a week are safer. Once your levels normalize, you shift to a maintenance schedule. Blood counts every 4 to 8 weeks determine how often you’ll need future sessions, which varies widely from person to person.
Interestingly, blood removed during therapeutic phlebotomy can sometimes enter the general blood supply. Under federal regulations, if you meet all standard donor eligibility criteria and your phlebotomy is prescribed for hereditary hemochromatosis (an iron overload condition), your blood can be used for transfusions without any special labeling. For other conditions, additional regulatory steps apply.
Why Your Red Blood Cells Are High
The underlying cause shapes the entire treatment approach. The major categories break down like this:
- Polycythemia vera (PV): A bone marrow disorder where a genetic mutation (called JAK2) causes your body to overproduce red blood cells on its own. This is the most common primary cause and requires ongoing management.
- Hereditary hemochromatosis: Your body absorbs too much iron from food, and excess iron drives red blood cell production. Phlebotomy here serves double duty, lowering both red cell counts and dangerous iron stores. Treatment targets a ferritin level below 50 during the initial phase and below 100 for long-term maintenance.
- Secondary causes: Smoking, living at high altitude, chronic lung disease, sleep apnea, or certain kidney conditions can all push your body to make more red blood cells. In these cases, treating the root cause often resolves the problem without ongoing phlebotomy.
When Phlebotomy Alone Isn’t Enough
For polycythemia vera specifically, some people need medication in addition to blood removal. This is typically the case when phlebotomies are needed very frequently, when platelet counts are also dangerously high, or when there’s a history of blood clots. Cytoreductive medications work by dialing down the bone marrow’s overproduction of blood cells. Low-dose aspirin is also commonly prescribed alongside phlebotomy to reduce clotting risk.
The decision to add medication is based on individual risk factors, particularly age over 60 and any prior clotting events. Many people with PV manage well with phlebotomy alone for years.
Addressing Reversible Causes
If smoking is contributing to your high red blood cell count, quitting can make a measurable difference. A study tracking polycythemic smokers found that about half successfully quit within three months of receiving cessation support, and blood parameters were reassessed at that point. The body gradually stops overcompensating once carbon monoxide levels from cigarettes drop and oxygen delivery normalizes.
Similarly, people who move from high altitude to lower elevation often see their hematocrit fall as their body no longer needs extra red blood cells to compensate for thinner air. Sleep apnea treatment, particularly consistent use of a CPAP machine, can also reduce red cell overproduction by correcting the overnight oxygen drops that trigger it.
What About Diet and Hydration?
If you’ve been told your blood is too concentrated, you might wonder whether cutting iron-rich foods or avoiding vitamin C (which enhances iron absorption) would help. For polycythemia vera, diet plays a minimal role. Specialists at Mayo Clinic have noted that food-based iron consumption doesn’t significantly impact red blood cell production in PV. The disease is driven by a bone marrow mutation, not by what you eat.
Hemochromatosis is slightly different. Because the core problem is excessive iron absorption, avoiding iron supplements, limiting red meat, and being cautious with vitamin C supplements around meals can support treatment. But phlebotomy remains the primary intervention even here.
Staying well hydrated matters for everyone with elevated hematocrit. Dehydration concentrates your blood, making thick blood even thicker. This doesn’t treat the underlying condition, but it reduces the immediate risk that comes with high blood viscosity, particularly the risk of clots. Aim to drink enough fluid that your urine stays pale yellow throughout the day, and increase intake during hot weather or exercise.
What to Expect During Treatment
The initial phase of phlebotomy can feel intense. Frequent blood draws over days or weeks may leave you fatigued, lightheaded, or short of breath, especially during exercise. These symptoms improve as your body adjusts. Over time, your iron stores will drop because each batch of removed blood takes iron with it. This is intentional in hemochromatosis but can occasionally cause iron deficiency symptoms in PV patients, including fatigue and cravings for ice or other non-food items.
Once you’re in the maintenance phase, the rhythm becomes more predictable. Some people need phlebotomy every few weeks, others every few months. Regular blood counts guide the schedule. The goal is straightforward: keep hematocrit below 45% in men and 42% in women to minimize the risk of clots, strokes, and heart attacks that come with thicker blood.