Problems with the blood can impede many functions of the body and cause a range of complications. For this reason, hematology —the study and treatment of blood disorders — is a subspecialty of internal medicine.

Hematologists work with blood-related conditions, including several types of cancer. They use a variety of tests and treatments for these issues.

Many hematologists also receive training in oncology, which is the branch of medicine dedicated to diagnosing and treating cancer.

This article will look at what hematology is, what hematologists do, and how their work relates to oncology.

a doctor looking at a blood vial in a hematology labShare on Pinterest
Hematologists carry out tests and procedures to help diagnose and treat problems with the blood.

Hematology is the study of blood in relation to health and disease.

Blood plays essential roles in human health, including:

  • transporting vital substances, such as oxygen and nutrients, around the body
  • helping to control the body’s balance of water and acidity
  • helping to fight off disease

Problems with the blood can affect several of the body’s systems, such as the lymphatic system, a network of tissues and organs that clear waste.

Blood disorders sometimes stem from problems with the bone marrow, where the body makes most of its blood cells.

Hematology aims to understand how these problems occur, how they affect a person’s health, and how to treat them.

Hematologists are medical doctors who specialize in diagnosing and treating problems with the blood and related structures, such as the bone marrow.

Tests and procedures that a hematologist may perform include:

  • Complete blood cell count: This test can help diagnose anemia, inflammatory diseases, and blood cancer. It can also help with monitoring blood loss and infection.
  • Platelet count: This test helps diagnose and monitor bleeding disorders.
  • Blood enzyme tests: There are many types of these tests, which a doctor uses to help diagnose cardiovascular conditions, including heart attack.
  • Bone marrow biopsy: This procedure can help diagnose and monitor anemia, thrombocytopenia, which involves having a low platelet count, and some cancers.
  • Blood transfusions: This involves the body receiving healthy blood intravenously — through an IV.

A hematologist might have one of the following specialties.


Hemoglobin is a protein in red blood cells that carries oxygen around the body. Hemoglobinopathy is the study of abnormal hemoglobin.

These abnormalities may indicate sickle cell disease, thalassemia, or other disorders. Each may cause episodes of pain.

Hematological malignancy

This area of hematology focuses on diagnosing and treating blood cancers, such as myeloma.

Blood cancers start in the cells of the immune system or tissues that make blood cells, such as bone marrow.


Anemias are conditions that lead to low levels of hemoglobin or red blood cells in the body.

Having anemia prevents enough oxygen-rich blood from circulating in the body. As a result, a person may feel unusually tired and experience muscle weakness.


Coagulopathy refers to disordered bleeding; it reflects the body’s ability to form blood clots.

Blood disorders, such as hemophilia, are forms of coagulopathy. They make it difficult for the body to control bleeding.

How does it relate to oncology?

It is common for hematologists to also train in oncology, which is the study, diagnosis, and treatment of cancer. The combined training allows these doctors to treat a range of blood-related illnesses, including some cancers.

A person with blood cancer, such as leukemia or myeloma, may see an oncologist and hematologist separately, or they may see a doctor with training in both fields.

Not everyone who receives a referral to an oncologist has cancer. Many oncologists train in hematology and see people with blood conditions that are not cancerous.

Various disorders and diseases primarily affect the blood and may be studied and treated by a hematologist.

Some examples include:

  • Anemia: This involves the body producing too few healthy red blood cells to carry enough oxygen around the body.
  • Sickle cell disease: This form of anemia changes the shape of red blood cells.
  • Thalassemia: This involves the body not making enough hemoglobin.
  • Bleeding disorders: These prevent the body from forming blood clots correctly.
  • Thrombocytopenia: This involves a low platelet count, which can result in difficulty forming blood clots.
  • Malaria: This infection can destroy red blood cells.
  • Von Willebrand’s disease: This bleeding disorder occurs in people who do not have a blood protein called von Willebrand factor.
  • Thrombosis: This refers to a clot in a blood vessel.
  • Hypercoagulability: This describes the blood’s increased tendency to clot.
  • Blood cancers: These can affect the function of a person’s blood cells.

Hematologists are medical doctors who specialize in blood-related conditions.

A variety of health issues can primarily affect the blood, from anemias to cancers, and hematologists provide a range of clinical tests and treatments.

The links between hematology and oncology mean that some doctors train in both. If a doctor refers a person to an oncologist, it may not mean that the doctor suspects cancer.