Hemoglobin 18.0 g/dL: Is That High?

Written by

Ernestas K.

Clinical research writer specializing in human health, biology, and preventive medicine.

Reviewed against ASH, NIH, Mayo Clinic, CDC guidelines · Last reviewed March 17, 2026

Is Hemoglobin 18.0 g/dL Low, Normal, or High?

Hemoglobin 18.0 g/dL is above the normal range and is considered elevated. The standard hemoglobin range is 12.5 to 17.5 g/dL, placing 18.5 above the upper limit. Hemoglobin is the oxygen-carrying protein in your red blood cells, and having too much of it can be a concern just as having too little can. An elevated hemoglobin level means your blood contains more red blood cells or more concentrated hemoglobin than typical, which can make your blood thicker and harder to circulate. This condition is generally referred to as polycythemia. While there are benign explanations for mildly elevated hemoglobin, this result warrants investigation by your doctor to determine the cause.

Hidden Risk of Hemoglobin 18.0 g/dL

A hemoglobin of 18.0 g/dL may not cause noticeable symptoms right away, but elevated hemoglobin carries risks that are important to understand. When your blood is thicker than normal, it moves more slowly through your vessels, and this can create problems in your circulatory system. The American Society of Hematology notes that persistently elevated hemoglobin increases the risk of several serious complications.

Risks associated with hemoglobin at 18.0 g/dL include:

• Blood clots, including deep vein thrombosis (DVT) in the legs and pulmonary embolism in the lungs
• Increased risk of stroke due to thickened blood moving through small vessels in the brain
• Heart attack risk rises because the heart has to work harder to pump thicker blood
• Headaches, dizziness, and blurred vision caused by sluggish blood flow to the brain
• High blood pressure, as thicker blood creates more resistance in the arteries
• Itchy skin, particularly after a warm shower or bath, which is a classic symptom of polycythemia vera
• Gout caused by elevated uric acid levels, which can occur when excess red blood cells break down

What Does a Hemoglobin Level of 18.0 g/dL Mean?

Hemoglobin is the oxygen-carrying protein inside your red blood cells. Each hemoglobin molecule picks up oxygen in your lungs and delivers it to cells throughout your body. When hemoglobin is measured at 18.0 g/dL, it means there is more of this protein in your blood than the body typically needs. While it might seem like more oxygen delivery would be a good thing, too much hemoglobin actually creates problems. Thicker blood does not flow as smoothly, and the increased viscosity can slow circulation, raise blood pressure, and increase the risk of clotting. The National Institutes of Health identifies several possible reasons for elevated hemoglobin. The most common is dehydration, which temporarily concentrates your blood and can make hemoglobin appear higher than it truly is. Living at high altitude is another common cause, as your body produces more red blood cells to compensate for lower oxygen levels in the air. Smoking can also raise hemoglobin because carbon monoxide from cigarettes reduces the oxygen-carrying efficiency of each hemoglobin molecule, prompting your body to make more. Chronic lung diseases like COPD can have a similar effect. In some cases, elevated hemoglobin points to polycythemia vera, a bone marrow disorder where the body produces too many red blood cells. Less common causes include kidney tumors, testosterone use, and certain performance-enhancing drugs. Your doctor can use additional tests to determine which category your elevation falls into.

Lifestyle Changes for Hemoglobin 18.0 g/dL

If your hemoglobin is elevated at 18.0 g/dL, certain lifestyle adjustments can help manage your levels while your doctor works to identify the cause. Hydration is the single most important factor. Dehydration concentrates your blood and raises hemoglobin readings, so drinking plenty of water throughout the day, especially in warm weather or during exercise, is essential. Aim for at least eight glasses of water daily, and more if you are physically active or live in a hot climate. If you smoke, quitting is strongly recommended. Smoking is one of the most common causes of elevated hemoglobin, and the Mayo Clinic lists smoking cessation as a key step in managing high hemoglobin. Your body produces extra red blood cells to compensate for the carbon monoxide in cigarette smoke, and stopping allows hemoglobin to normalize over time. Regular moderate exercise helps maintain cardiovascular fitness, but avoid extreme endurance training at high altitudes, as this can further stimulate red blood cell production. If you live at high elevation, be aware that some degree of elevated hemoglobin is a natural adaptation, but discuss with your doctor what level is safe for you. Avoid very hot baths and saunas if you experience itchy skin, as heat can worsen this symptom. Be mindful of any supplements or substances that might increase red blood cell production, including anabolic steroids or testosterone, and discuss these with your doctor.

Diet Changes for Hemoglobin 18.0 g/dL

Dietary changes can play a supporting role in managing elevated hemoglobin, though they are not a substitute for medical evaluation and treatment. The primary dietary goal when hemoglobin is high is to stay well hydrated and avoid factors that further increase red blood cell production. According to the NIH, certain dietary choices can help support healthier blood viscosity and overall cardiovascular health.

Dietary considerations for hemoglobin at 18.0 g/dL include:

• Drinking plenty of water, herbal teas, and other hydrating fluids throughout the day to help thin the blood naturally
• Eating foods rich in omega-3 fatty acids such as salmon, mackerel, walnuts, and flaxseed, which support cardiovascular health and may help with blood flow
• Including antioxidant-rich fruits and vegetables like berries, tomatoes, and leafy greens to support overall vascular health
• Reducing or avoiding alcohol, which can dehydrate you and affect blood cell production
• Being mindful of excessive iron intake from supplements, as extra iron can fuel additional hemoglobin production when levels are already high
• Avoiding iron-fortified cereals and multivitamins with iron unless your doctor specifically recommends them
• Limiting red meat intake if your doctor suggests it, since red meat is a significant source of dietary iron and may contribute to further elevation

Hemoglobin 18.0 g/dL in Men, Women, Elderly, and Kids

A hemoglobin of 18.0 g/dL is above the normal range for all groups, but the degree of elevation varies. For adult men, the Mayo Clinic lists the normal range as 13.5 to 17.5 g/dL. At 18.5, a man is 1.0 g/dL above the upper limit, which is a moderate elevation that requires investigation but may have a benign explanation such as dehydration, high altitude living, or smoking. For adult women, the normal range is 12.0 to 15.5 g/dL, making 18.5 significantly elevated, roughly 3.0 g/dL above the upper normal limit. In women, a reading this high is more unusual and more likely to prompt immediate investigation. Possible causes specific to women include testosterone therapy, polycythemia vera, or chronic hypoxia from lung conditions. In elderly adults, hemoglobin tends to decrease naturally with age, so a reading of 18.0 in an older person is particularly noteworthy. It could suggest dehydration, which is common in elderly individuals, or a bone marrow disorder. The CDC recommends that unexplained elevations in older adults be evaluated promptly. In children, hemoglobin levels vary widely by age, but 18.5 would be above normal for most pediatric age groups except possibly newborns, who naturally have very high hemoglobin in the first few weeks of life. In older children and adolescents, a reading of 18.0 would be considered high and warrants evaluation for congenital heart disease, chronic hypoxia, or other causes.

Medicine Effects on Hemoglobin 18.0 g/dL

Several medications and substances can raise hemoglobin levels, and reviewing your current medications with your doctor is important when your result is 18.0 g/dL. The NIH and ASH both note that drug-induced polycythemia is more common than many people realize, particularly with hormone therapies.

Medications and substances that may increase hemoglobin include:

• Testosterone replacement therapy, which is one of the most common medication-related causes of elevated hemoglobin in men
• Anabolic steroids, whether prescribed or used for performance enhancement, which stimulate red blood cell production
• Erythropoietin (EPO) injections, used to treat anemia in kidney disease patients, which can raise hemoglobin above target levels if dosing is not carefully monitored
• Diuretics, which can concentrate the blood through fluid loss, making hemoglobin appear higher than it truly is
• Certain blood doping substances used in athletics, which artificially boost red blood cell counts
• High-dose iron supplements when taken unnecessarily, which provide raw material for excess hemoglobin production
• Cobalt supplements, which mimic hypoxia signals in the body and stimulate red blood cell production

If you are taking any of these medications, your doctor may need to adjust your dosage or monitor your blood counts more frequently. Never stop prescribed medications without consulting your healthcare provider first.

When to Retest Hemoglobin 18.0 g/dL

A hemoglobin of 18.0 g/dL should be confirmed with a repeat test relatively soon. Your doctor will likely order a follow-up blood draw within one to two weeks, especially if this is the first time your hemoglobin has tested above normal. Before the repeat test, your doctor may advise you to stay well hydrated to rule out dehydration as a cause. If the repeat test still shows elevated hemoglobin, additional testing will likely follow, including a complete blood count with red blood cell indices, erythropoietin levels, iron studies, and possibly genetic testing for conditions like polycythemia vera. The Mayo Clinic notes that a JAK2 gene mutation test is commonly ordered when polycythemia vera is suspected. If a diagnosis is established and treatment begins, such as therapeutic phlebotomy to reduce red blood cell volume, hemoglobin will be checked regularly, often every few weeks at first, then monthly as levels stabilize. If a reversible cause is identified, such as dehydration or a medication side effect, retesting after the correction will help confirm that levels have normalized. Long-term monitoring frequency depends on the underlying cause, but most people with a history of elevated hemoglobin will need blood work at least every three to six months.

Hemoglobin 18.0 g/dL — Frequently Asked Questions

When to See a Doctor About Hemoglobin 18.0 g/dL

A hemoglobin of 18.0 g/dL is above the normal range and should be evaluated by a doctor. Schedule an appointment within the next few days to discuss this result and get a plan for follow-up testing. Seek more urgent medical attention if you are experiencing symptoms such as persistent headaches, dizziness, blurred vision, chest pain, shortness of breath, redness or warmth in your face and hands, numbness or tingling in your extremities, or unexplained itching especially after warm showers. These symptoms can suggest that thickened blood is affecting circulation and need to be assessed promptly. The ASH recommends that anyone with hemoglobin consistently above 18.0 g/dL be evaluated for underlying causes including polycythemia vera, which requires ongoing management to prevent complications like blood clots, stroke, and heart attack. If you are currently taking testosterone therapy or other medications known to raise hemoglobin, contact your prescribing doctor to report this result. They may need to adjust your dose and increase monitoring frequency. Do not ignore this result even if you feel fine, because the risks associated with high hemoglobin, particularly blood clots, can develop without warning symptoms. Early evaluation and monitoring are the best ways to protect your health.