Chronic lymphocytic leukemia: Blood tests for diagnosis and treatment

By Nicole Ferrara • February 9, 2023

Estimated reading time: 4 minutes

By Nicole Brudos Ferrara

"Chronic lymphocytic leukemia, or CLL, is one of the most common types of leukemia in the U.S. adult population," says Sameer Parikh, M.B.B.S., a hematologist and oncologist at Mayo Clinic. "It is a disease that typically affects older men, and the median age at the time of diagnosis is about 72."

Chronic lymphocytic leukemia is a blood and bone marrow cancer that occurs when the bone marrow makes too many lymphocytes, a type of white blood cell. The disease begins when the DNA of blood-producing cells cause them to produce abnormal lymphocytes. These abnormal lymphocytes multiply and accumulate in the blood and specific organs, crowding healthy cells out of the bone marrow and interfering with blood cell production.

"The vast majority of patients with chronic lymphocytic leukemia are diagnosed incidentally through a routine health checkup or blood draw that shows an abnormality," says Dr. Parikh. "About 10% to 20% of patients have symptoms — lymph gland enlargement, fatigue, abdominal discomfort or some bleeding — that may prompt medical attention."

Blood tests play a crucial role in diagnosing and treating chronic lymphocytic leukemia. Here's what Dr. Parikh wants you to know:

Chronic lymphocytic leukemia should be confirmed with a blood test, and treatment may not be immediately necessary.

Confirming a correct diagnosis of chronic lymphocytic leukemia is essential before deciding on a treatment plan. "The diagnosis is typically established by a blood test called flow cytometry," says Dr. Parikh.

Flow cytometry, or immunophenotyping, helps determine whether an increased number of lymphocytes is due to chronic lymphocytic leukemia, a different blood disorder, or your body's reaction to an infection.

"Typically, when we see patients at Mayo Clinic, we repeat the flow cytometry test in our lab to ensure that the patient truly has chronic lymphocytic leukemia because other diseases — particularly types of lymphoma — can be confused with this diagnosis," says Dr. Parikh.

Once a diagnosis of chronic lymphocytic leukemia is confirmed, you won't immediately receive treatment unless you're experiencing symptoms. This approach is supported by decades of medical research at Mayo Clinic and other cancer centers.

"Over the last 30 years, we've done multiple clinical trials in which patients with early stage disease were randomly assigned to receive treatment or no treatment. These trials have consistently found no benefit to early intervention," says Dr. Parikh.

Blood tests also help determine how chronic lymphocytic leukemia will progress.

At Mayo Clinic, your care team will conduct additional blood tests to determine how quickly your disease will progress. One of these tests, fluorescence in situ hybridization (FISH), examines the chromosomes inside the cancerous lymphocytes to look for changes. Another test determines the mutation status of the immunoglobulin heavy chain (IGHV) gene of the cancerous lymphocytes.

"We use findings from these tests to calculate a score called the CLL international prognostic index," says Dr. Parikh.

This index assigns a person with chronic lymphocytic leukemia to one of four risk groups: low, intermediate, high, and very high. The low-risk group has the lowest chance of needing treatment in five years, and nearly all people in the very high-risk group will need treatment in five years, explains Dr. Parikh. These risk groups relate to the risk of the disease requiring treatment rather than how well a patient might respond to treatment once it is needed.

Dr. Parikh says this testing and scoring system works for most people with chronic lymphocytic leukemia and allows health care professionals to counsel them on next steps. "We strongly believe in this because it empowers our patients to understand their risk and what to expect in the future," he says.

According to Dr. Parikh, a person with chronic lymphocytic leukemia who has no symptoms and is otherwise feeling well would be followed with regular checkups and blood tests. "When they develop symptoms, that would merit treatment. On average, that takes about four to five years," he says.

When treatment is needed, blood tests will continue to play a role.

The testing and scoring system used to confirm the diagnosis and predict the progression of chronic lymphocytic leukemia also helps health care professionals determine the best treatment approach.

"CLL is considered an indolent disease, meaning it progresses slowly. As the disease progresses, you can treat it; and people respond very well to treatment," says Dr. Parikh.

At Mayo Clinic, your care team will continue to use regular blood tests at each stage of your disease to ensure they're offering you the best care and guidance.

"Many different types of treatment are available for chronic lymphocytic leukemia," says Dr. Parikh. "We account for the genetic profile of the disease, the health history of the patient — whether they have co-morbidities such as cardiovascular disease or renal disease — and we ask patients about their preferred treatment based on their goals for care."

Dr. Parikh says understanding the genetic characteristics of the disease is particularly important in determining a treatment plan, as research has shown that some genetic profiles respond better to specific treatments.