Can You Be Diagnosed with AML with Less Than 20% Blasts?

Yes, you can absolutely be diagnosed with acute myeloid leukemia (AML) even if your blast count is under 20%.

For decades, the standard medical rule was that a patient needed to have 20% or more leukemia cells (called blasts) in their bone marrow or blood to be officially diagnosed with AML. If the count was lower—typically between 10% and 19%—patients were usually diagnosed with a related condition called myelodysplastic syndrome (MDS) with excess blasts.

However, modern medicine has shifted away from relying strictly on a raw percentage. Today, doctors use advanced genetic testing to look at the unique DNA of the leukemia cells. Both major organizations that define cancer criteria—the World Health Organization (WHO) and the International Consensus Classification (ICC)—updated their guidelines in 2022 to reflect this new understanding ^[1][2].

The Role of Defining Genetic Abnormalities

Leukemia is driven by genetic mutations inside your blood cells. Researchers have found that certain genetic abnormalities are so specific to AML that their presence alone confirms the diagnosis, regardless of how many blasts are currently in your body ^[3][4].

You can typically find the results of these tests in your medical portal under “molecular pathology” or “cytogenetics,” often referring to testing methods like NGS (Next-Generation Sequencing), FISH, or PCR.

If these tests show any of the following genetic markers, both the WHO and ICC agree you have AML even if your blast count is below 20% (in fact, there is no minimum blast requirement at all for these) ^[5][3]:

• PML::RARA: The hallmark of acute promyelocytic leukemia (APL), a unique subtype that requires its own immediate, specialized treatment.
• RUNX1::RUNX1T1
• CBFB::MYH11

Other specific genetic markers, such as NPM1 mutations and KMT2A rearrangements, also override the 20% rule. Under the 2022 WHO guidelines, the 20% threshold is removed entirely for these features ^[2][3]. The ICC guidelines similarly recognize these cases but also introduce a 10% blast threshold for certain other high-risk mutations (like TP53) ^[6][2].

The MDS/AML Overlap

What if your blast count is between 10% and 19%, but you don’t have one of those specific genetic abnormalities?

The ICC guidelines recently created a new diagnostic category called MDS/AML for this exact situation ^[7][8]. This name reflects the clinical reality that disease with 10–19% blasts often behaves much more like aggressive AML than slower-moving MDS ^[9][10]. Recognizing this overlap ensures that patients aren’t left waiting for their blast count to reach an arbitrary 20% mark before getting the treatments they need ^[6][11].

Why This Matters for Your Treatment

Being diagnosed with AML at a lower blast percentage is a vital step in your care because it dictates your treatment options.

Historically, patients with 10–19% blasts were sometimes given less aggressive treatments for MDS. We now know that leukemia driven by these specific genetic markers acts like AML and needs to be treated like AML right away ^[12][13]. By categorizing your condition accurately based on its genetic makeup rather than just a blast count, your care team can immediately start you on the most appropriate targeted therapies or prepare you for treatments like a stem cell transplant, ensuring you get the right treatment at the right time ^[11][14].