When I perform a physical, only about 10% of what I do involves reviewing lab tests. Another 20% is the physical exam itself, and the remaining 70% is the conversation.

Most patients believe lab results are the most important part of a medical visit. While these do hold tremendous value, they aren’t the whole story. Getting to the root cause of a problem often requires thoughtful conversation, deeper investigation, and a willingness to look beyond the numbers.

One key part of regular lab testing is the CBC, or complete blood count, which includes a look at your hemoglobin level. This important metric can tell us a lot about your health, which is why an abnormal result often spurs patients to ask questions like:

• What does low hemoglobin mean? 
• Are anemia and low hemoglobin the same thing? 
• What type of cancer causes low hemoglobin?

Getting answers to questions like these can help you be an active and informed participant in your health. Let’s dive in.

What Is Hemoglobin?

Hemoglobin is a protein in red blood cells that carries oxygen throughout your body. Without hemoglobin, your body can’t transport the oxygen you breathe to the organs and tissues that need it.

We all know instinctively that we can’t live without certain resources. The survival “Rule of Three” specifies that we can survive three weeks without food, three days without water, three hours without shelter, and only three minutes without air. That’s how crucial oxygen — and, therefore, hemoglobin — is.

Normal laboratory values for hemoglobin fall into these generalized ranges:

• 13.5–16.5 grams per deciliter for men
• 11.5–16 grams per deciliter for women

A similar test result you’ll see in your CBC is your hematocrit, which shows the percentage of red blood cells in your total blood volume. Since hemoglobin is found inside red blood cells, a low hematocrit and low hemoglobin often (though not always) go hand in hand. In this blog post, we’ll focus strictly on hemoglobin.

What Is Low Hemoglobin, and Why Does It Matter?

A low value in your hemoglobin test result means your blood lacks an adequate amount of hemoglobin. This condition, also called anemia, results in your blood not carrying enough oxygen throughout your body.

To understand how this happens, we need to discuss the life cycle of blood.

Your body is constantly losing and producing blood. It’s a normal, natural occurrence. The average red blood cell lives around 120 days before being broken down and processed as waste. That constant loss and replacement means your bone marrow — your body’s red blood cell factory — must keep supplying new cells to maintain a healthy balance.

Causes of Low Hemoglobin

Low hemoglobin develops when the body loses blood faster than it can be replaced. There are three main causes:

• Loss of blood: Most commonly from internal gastrointestinal bleeding. This could be because of a stomach ulcer, colon cancer, or chronic use of anti-inflammatory medications like ibuprofen or aspirin, which can irritate the gut lining.
• Destruction of blood: Known as hemolysis; causes include blood cancers like leukemia and lymphoma, certain antibiotics, anti-anxiety medications like lorazepam, immunosuppressants used in organ transplants, and chemotherapy.
• Inability to produce blood: Often due to kidney failure (since kidneys produce erythropoietin, a hormone that stimulates blood production), iron deficiency, or cancers affecting bone marrow, such as myelodysplastic syndrome, leukemia, lymphoma, and multiple myeloma. Other contributors include vitamin B12 deficiency and acid-reducing medications like proton pump inhibitors (PPIs) and H2 blockers that hinder iron absorption.

When evaluating hemoglobin levels in CBC results, it’s most helpful to look at trends over time. A “normal” number on the low end might actually hide a concerning downward pattern. If your hemoglobin was 15.5 a year ago and is now 13.5, that’s a red flag, even if 13.5 technically falls within the “normal” range.

On the other hand, trends may demonstrate that a low result isn’t concerning, though it looks worrisome in isolation. People with a genetic condition called thalassemia have consistently low hemoglobin levels, but they may not necessarily require treatment.

Symptoms of Low Hemoglobin

Low hemoglobin can show up in many ways, often with symptoms so general that they’re easy to overlook. Symptoms include:

• Fatigue
• Weakness
• Shortness of breath
• Pale skin
• Headaches

If you’re experiencing these symptoms, it’s a clue that there may be a deeper issue. But these signs alone don’t tell us the cause.

That’s where the CBC comes in to guide further testing.

What Type of Cancer Causes Low Hemoglobin?

Patients sometimes ask, “What type of cancer causes low hemoglobin?”

A low hemoglobin result doesn’t automatically mean you have cancer. Whenever we detect low hemoglobin, however, we have to consider cancer as a potential cause unless there’s an obvious alternative explanation, such as a nutrient deficiency or medication side effect.

Several types of cancer may cause low hemoglobin:

• Colon cancer: Can cause hidden internal bleeding, leading to gradual blood loss and anemia.
• Blood cancers: Leukemia, lymphoma, multiple myeloma, and myelodysplastic syndromes directly interfere with the bone marrow’s ability to produce healthy red blood cells.

Routine blood tests are critical for early cancer detection. Sometimes, the only early sign of cancer is a subtle drop in hemoglobin. That’s why checking your blood counts regularly and comparing them over time is so important.

Next Steps if You’re Experiencing Possible Low-Hemoglobin Symptoms

If you’re dealing with symptoms like unexplained fatigue, shortness of breath, or pale skin, the first step is to visit your doctor. After ruling out heart or lung problems, a simple CBC can be illuminating.

If your hemoglobin level comes back as abnormal, the next step is to look for the underlying cause. This will likely involve additional blood tests to determine which of the factors mentioned in this post could be influencing either blood loss, destruction, or production.

Sometimes, we find a simple issue like a nutrient deficiency, where a supplement or change in diet addresses the problem. Other times, we uncover more serious conditions. Whatever you find, you and your doctor can work together to address the root cause appropriately.

Get to the Root: Final Thoughts on Low Hemoglobin

Many people who come to see me with generalized symptoms like fatigue are hoping for a magic-bean solution — a quick fix like a B12 shot or iron supplement. But as a functional medicine physician, I believe true medicine lies in addressing the root cause, not just treating symptoms.

If we treat your symptoms without investigating the reason behind them, we might unintentionally mask a serious underlying condition, like cancer. It’s better to get to the source of the problem early rather than allow an illness to brew undetected.

So, whether you’re curious about your lab results or you’re worrying about what type of cancer causes low hemoglobin, I encourage you to have a conversation about lab trends and root causes with your doctor. Understanding what your specific results mean in context will empower you to make the best decisions for your health and future.