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Diagnosis and tests

How APL is diagnosed

The related article (“APL: symptoms, emergency signs and diagnosis”) explains why the bone marrow is examined. This topic looks at the special, fast path to an APL diagnosis, from suspicion to genetic confirmation.

Last updated: ~1 min read
Cells with granules.
Figure 1.Abnormal promyelocytes on a smear.

01Short answer

Diagnosing APL demands speed. The first step is a blood count and smear: a specialist sees abnormal promyelocytes with heavy granules and sometimes bundles of Auer rods. At the same time, clotting tests (prothrombin time, fibrinogen, D-dimer) show DIC. Together these findings strongly suggest APL, and treatment starts straight away. On flow cytometry, APL cells show a characteristic pattern (for example CD34 and HLA-DR are usually negative). Confirmation is genetic: FISH or PCR finds t(15;17) and the PML::RARA fusion. PCR is also used to follow MRD after treatment. A bone marrow test is done, but when the risk of bleeding is high, the diagnosis is sometimes made from blood.

02Simple explanation

Smear + clotting tests = suspicion.

Treatment at once.

PML::RARA: confirmation.

03Scientific explanation

Fast genetics: FISH or RT-PCR for PML::RARA often gives a result within 24–48 hours.

Clotting monitoring: fibrinogen and platelets are checked often in the first days and supported with blood products.

04What happens in the body?

Suspicion on the smear

Abnormal promyelocytes suggest APL.

Clotting tests

Fibrinogen and other tests show DIC.

Tubes with blue caps.
Figure 2.Clotting test tubes.

Genetic confirmation

The PML::RARA fusion confirms the diagnosis.

A yellow fusion dot and a PCR curve.
Figure 3.PML::RARA confirmation.

05Diagnosing APL

Four steps.

Smear — Promyelocytes.1SmearPromyelocytes.
Clotting — DIC checked.2ClottingDIC checked.
Treatment — Starts at once.3TreatmentStarts at once.
Genetics — PML::RARA.4GeneticsPML::RARA.

06Tests in diagnosing APL

TestWhat it shows
Blood smearAbnormal promyelocytes, Auer rods
Clotting testsDIC, low fibrinogen
Flow cytometryA characteristic marker pattern
FISHt(15;17)
RT-PCRPML::RARA, baseline for MRD

07Key terms

APL
Acute promyelocytic leukaemia.
PML::RARA
The APL fusion gene.
DIC
Disseminated intravascular coagulation.
D-dimer
A breakdown product of clots.
Fibrinogen
A clotting protein.

08Key points

  • Diagnosing APL demands speed.
  • The smear and clotting tests come first.
  • Treatment does not wait for confirmation.
  • PML::RARA confirms the diagnosis.
  • PCR follows MRD.
  • Clotting is checked often.

09Frequently asked questions

Why does treatment start before confirmation?

Because the risk of bleeding is high in the first days; early treatment lowers it.

Is a marrow test essential?

It is usually done, but because of the bleeding risk, blood is sometimes enough.

When is PCR repeated?

At set points in treatment, to measure MRD.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Why does treatment start before confirmation?

  2. Is a marrow test essential?

  3. When is PCR repeated?

My questions

12Sources

  1. National Cancer Institute (NCI). Adult AML treatment (PDQ), patient version
  2. National Cancer Institute (NCI). Definition: FISH
  3. National Cancer Institute (NCI). Definition: polymerase chain reaction
  4. MedlinePlus. Cerebrospinal fluid (CSF) analysis
  5. MedlinePlus (U.S. National Library of Medicine). Creatinine Test
  6. MedlinePlus (U.S. National Library of Medicine). Glomerular Filtration Rate (GFR) Test
  7. MedlinePlus (U.S. National Library of Medicine). Lactate Dehydrogenase (LDH) Test
  8. MedlinePlus (U.S. National Library of Medicine). Prothrombin Time Test and INR (PT/INR)
  9. NHS. Echocardiogram
  10. NHS. Electrocardiogram (ECG)
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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