Diagnosis

Diagnosing chronic myelomonocytic leukemia (CMML) usually involves a series of repeated tests, including blood and bone marrow tests. Your doctor usually can't confirm a diagnosis of CMML with one lab test result that shows abnormal blood counts. Instead, he or she will monitor you over a period of time with repeated lab tests that show abnormal blood counts. This is done to rule out other diagnoses.

Bone marrow testing involves two steps usually done at the same time in a doctor's office or a hospital:

  • A bone marrow aspiration to remove a liquid marrow sample; and
  • A bone marrow biopsy to remove a small amount of bone filled with marrow.

A hematopathologist examines the samples of your blood and marrow to confirm a diagnosis, identify the CMML subtype and look for damage to your chromosomes. A hematopathologist is a specialist who studies blood cell diseases by examining samples of blood cells, bone marrow cells and other tissues.

The hematopathologist looks for the following to identify CMML:

  • Persistent high levels of monocytes in the blood
  • No evidence of a Philadelphia chromosome. This is seen in a similar disease known as “chronic myeloid leukemia” (CML). This can be determined based on a blood test looking for a particular abnormality known as a BCR/ABL fusion gene.
  • Less that 20 percent of blast cells in the blood and bone marrow
  • Abnormalities in one or more types of precursor cells that develop into red blood cells, certain types of white blood cells or platelets

Other Diagnostic Tests

Your doctor may order one or more tests such as those below to diagnose CMML:

  • X-rays or computed tomography (CT) scans detect an enlarged spleen or liver.
  • Blood and urine tests detect high levels of lysozyme, an enzyme found in saliva, tears and some immune cells like monocytes.
  • Additional blood work looks for high levels of proteins called lactate dehydrogenase (LDH) and beta 2-microglobulin, which can indicate tissue damage and increased white-cell production or destruction caused by inflammation or certain types of cancer.

Cytogenetic and Molecular Abnormalities

Cytogenetic abnormalities refer to abnormal changes in chromosomes, which may include broken, missing, rearranged or extra chromosomes. Approximately 20 to 30 percent of CMML patients have chromosomal abnormalities. Some chromosomal abnormalities can affect prognosis and treatment. 

Molecular abnormalities refer to abnormal changes in genes. These abnormalities are known as gene mutations. Mutations that are acquired and not inherited are called "somatic mutations." In CMML, almost 90 percent of patients exhibit one or more somatic mutation. Some molecular abnormalities can affect prognosis and treatment.

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