A blood disease is any condition that affects how your blood cells or proteins function. Because blood has several distinct components, each with its own job, there are dozens of blood diseases ranging from common and easily treatable (like iron-deficiency anemia) to rare and life-threatening (like leukemia). Understanding the basics of what blood does helps make sense of what can go wrong.
Blood has four main components: red blood cells that carry oxygen, white blood cells that fight infection, platelets that help your blood clot, and plasma, the liquid portion containing proteins and clotting factors. A blood disease can target any one of these components, and the symptoms you experience depend on which part is affected.
Red Blood Cell Disorders
Red blood cells carry oxygen from your lungs to every tissue in your body. When something goes wrong with these cells, the result is usually some form of anemia, the most common type of noncancerous blood disorder. Anemia means you don’t have enough healthy red blood cells, or the ones you have don’t work properly. The underlying cause varies widely.
Iron-deficiency anemia is the most common type. Your bone marrow needs iron to make hemoglobin, the protein inside red blood cells that binds to oxygen. Without enough iron, your body simply can’t produce enough functional red blood cells. This can result from a diet low in iron, heavy menstrual periods, or chronic blood loss from conditions like ulcers.
Sickle cell disease is an inherited condition where an abnormal form of hemoglobin forces red blood cells into a rigid, crescent shape. These misshapen cells die much faster than normal, creating a constant shortage. They can also clump together and block small blood vessels, causing episodes of severe pain. Thalassemia is another inherited disorder where the body produces less hemoglobin than normal, leading to chronic anemia that ranges from mild to severe depending on the genetic variant.
Other forms include aplastic anemia, where the bone marrow stops producing enough blood cells altogether, and hemolytic anemias, where red blood cells are destroyed faster than the body can replace them. Some hemolytic anemias are caused by the immune system mistakenly attacking its own red blood cells.
White Blood Cell Disorders
White blood cells are your immune system’s front line. When their numbers are too high or too low, it signals something significant. A high white blood cell count may indicate an infection, inflammation, or cancer. A low count can point to vitamin deficiencies, autoimmune conditions, or cancer treatment side effects, and it leaves you more vulnerable to infections.
The most serious white blood cell disorders are blood cancers. Leukemia involves the rapid, uncontrolled growth of abnormal white blood cells in the bone marrow, crowding out healthy cells. Lymphoma is a cancer of the lymphatic system, which includes your lymph nodes, spleen, and bone marrow. Multiple myeloma targets plasma cells, a specific type of white blood cell that normally produces antibodies to fight infection. In myeloma, cancerous plasma cells accumulate in the bone marrow and produce abnormal proteins instead of healthy antibodies.
A specific drop in one type of white blood cell can also cause problems. Neutropenia, for instance, is a low count of neutrophils (the white blood cells most responsible for fighting bacterial infections) and can make even minor infections dangerous.
Platelet and Clotting Disorders
Platelets are tiny cell fragments that rush to the site of an injury and stick together to form a plug, stopping bleeding. If your platelet count drops too low (a condition called thrombocytopenia), you bruise easily, bleed longer from cuts, and may notice tiny red or purple spots on your skin called petechiae. Thrombocytopenia can happen because the bone marrow isn’t producing enough platelets, the spleen is trapping too many of them, or the immune system is destroying them.
Clotting also depends on proteins in your plasma called clotting factors. When these proteins are missing or defective, you get a bleeding disorder. Hemophilia A, the most common type of hemophilia, occurs when you’re missing or have low levels of one specific clotting factor. People with hemophilia often experience bleeding into joints and muscles, sometimes delayed by up to a day after an injury. Von Willebrand disease is the most common inherited bleeding disorder overall and typically causes milder symptoms, like prolonged bleeding after dental work or surgery, heavy menstrual periods, and easy bruising.
On the opposite end, some clotting disorders cause your blood to clot too much or in the wrong places. Conditions like antiphospholipid syndrome or certain genetic mutations can increase the risk of dangerous blood clots forming in veins or arteries.
Plasma Protein Disorders
Plasma makes up about 55% of your blood volume and carries two key groups of proteins: albumin and globulins. Albumin keeps fluid inside your blood vessels and transports hormones, vitamins, and medications throughout the body. Globulins help fight infections and move nutrients.
When albumin levels drop, it can be a sign of liver disease, kidney disease, or malnutrition. High globulin levels may point to autoimmune conditions like lupus, chronic infections like tuberculosis, or blood cancers including multiple myeloma and Hodgkin disease. These protein imbalances aren’t diseases in themselves but often serve as important clues that something deeper is going on.
Inherited vs. Acquired Blood Diseases
Some blood diseases are passed down through families. Sickle cell disease, thalassemia, hemophilia, and von Willebrand disease are all caused by genetic mutations present from birth. If you have a family history of any of these conditions, genetic testing can determine whether you carry the relevant gene.
Others develop during your lifetime. You can acquire a bleeding disorder from liver disease (since the liver produces many clotting factors), from vitamin K deficiency (which your body needs to make certain clotting proteins), or as a side effect of medication. Some conditions, like von Willebrand disease, can be either inherited or acquired. Iron-deficiency anemia is almost always acquired, usually through diet, blood loss, or pregnancy.
Common Symptoms
Because blood touches every organ in your body, blood diseases can produce a wide range of symptoms. The specific signs depend on which blood component is affected, but several symptoms appear across many blood disorders:
- Persistent fatigue and weakness, especially common in anemias where tissues aren’t getting enough oxygen
- Easy bruising or prolonged bleeding, pointing to platelet or clotting factor problems
- Frequent or severe infections, suggesting low or dysfunctional white blood cells
- Tiny red spots on the skin (petechiae), a hallmark of low platelet counts
- Unexplained weight loss, which can signal blood cancers
- Swollen lymph nodes, often associated with lymphoma or leukemia
- Bone pain or tenderness, sometimes caused by cancerous cells crowding the bone marrow
- Night sweats and fever, which can accompany blood cancers and severe infections
Many of these symptoms overlap with other conditions, which is why blood testing is central to diagnosis.
How Blood Diseases Are Detected
The most common starting point is a complete blood count, or CBC. This routine blood test measures the levels of red blood cells, white blood cells, and platelets in a single sample. Normal adult ranges give doctors a baseline for comparison. For example, a healthy hemoglobin level falls between 13.2 and 16.6 grams per deciliter for men and 11.6 to 15 for women. A normal platelet count ranges from roughly 135 to 371 billion per liter, depending on sex. White blood cells normally fall between 3.4 and 9.6 billion cells per liter.
When a CBC shows values outside the expected range, further testing narrows down the cause. This might include checking iron levels, examining blood cells under a microscope, measuring clotting times, or testing plasma protein levels. For suspected cancers, a bone marrow biopsy can reveal abnormal cell growth directly at the source.
Gene Therapy for Blood Diseases
Treatment for blood diseases has traditionally ranged from simple supplements (iron pills for iron-deficiency anemia) to blood transfusions and bone marrow transplants for severe conditions. But a major shift happened in December 2023 when the FDA approved the first gene therapies for sickle cell disease.
One of these treatments uses CRISPR, a genome-editing tool that can precisely cut and modify DNA. A patient’s own blood stem cells are removed, edited in a lab to boost production of a form of hemoglobin that prevents red blood cells from sickling, and then infused back into the body. In clinical trials, 93.5% of patients who received this therapy went at least 12 consecutive months without a severe pain crisis. The second approved therapy uses a different technique to insert a gene that produces a modified hemoglobin, with 88% of patients achieving complete resolution of pain episodes.
Both treatments require high-dose chemotherapy beforehand to clear room in the bone marrow for the modified stem cells, making the process intensive. They’re currently approved for patients 12 and older with severe sickle cell disease. These therapies represent a potential one-time treatment for a disease that previously required lifelong management.