Case of the Month: February 2026

Clinical history

A previously healthy 44-year old male presented to the Emergency Department with a 2 week history of fatigue and generalized weakness. Over the last few days, he has also developed a fever, which prompted him to seek medical attention. On further questioning, he endorses recent gingival bleeding along with easy bruising in his extremities, which is confirmed on physical exam. The remainder of the history and exam are unremarkable.

To begin the workup, the emergency physician orders a complete blood count along with routine coagulation testing (PTT, INR) given his recent history of bleeding. The relevant results of these tests are as follows.

• Hemoglobin 74 g/L
• MCV 87 fL
• Platelets 22 x 109/L
• WBC 1.0 x 109/L
• Absolute neutrophil count 0.4 x 109/L
• PTT: 46s
• INR: 1.6

You are the hematopathologist on service for your hospital, and are called by one of the laboratory technicians to look at the peripheral blood film for this patient. You review the clinical history and bloodwork before putting the slide under your microscope. Select images from the film are shown below.

Questions:

1. What is the predominant red blood cell morphologic abnormality seen in the image of the peripheral blood film? Name three conditions which can result in this finding.
2. The technician identified the white blood cells in the image as concerning for blasts. On scanning the rest of the slide, you see many of these same cells. What are some typical features which can be helpful in identifying blasts in peripheral blood? How would you describe the morphology of these blasts in particular?
3. You urgently call the clinician and treatment is quickly initiated based on your preliminary morphologic assessment. Based on the laboratory findings, clinical context, and morphology of the blasts, what is your suspected diagnosis and why? (Hint: specific treatment was started even before the diagnosis is confirmed!)
4. What additional investigations and testing modalities will help you confirm the diagnosis? Bonus: name the molecular rearrangement which is diagnostic for this specific entity.
5. Both the PTT and INR for this patient are elevated. Why do you think this is the case? What additional coagulation parameter may be useful to evaluate for this?

How to participate

Take a look at the images.

Anyone is welcome to try to solve the puzzle by commenting on the related post on our Instagram.

If you are a medical student at the University of Toronto, you can also:

• Fill out the online form
• Join the related lecture

Join the Special Interest Group in Laboratory Medicine to learn more about Laboratory Medicine.