WBC Morphology

A written description of how your white blood cells look under a microscope, such as their shape, granules and any immature cells.

AI-verified against cited sources. Awaiting expert reviewAlso called WBC morphLOINC 11156-7

What it is

White blood cells come in several types, and each has a usual look under a microscope. A lab professional, sometimes helped by a digital imaging system, looks at a stained drop of your blood spread on a glass slide. They write down anything that stands out in the white cells, such as extra granules, unusual shapes or immature cells. This comment is usually added when your blood count has a flag or when your clinician asked for a smear review. It adds detail to the numbers in your differential.

Why it matters

Your white blood cell count gives numbers. The smear shows what the cells look like, and that can add useful context. Changes such as toxic-looking granules in neutrophils or reactive lymphocytes are often seen when the body is responding to an infection or inflammation. Neutrophils with extra nuclear lobes are linked to low vitamin B12 or folate. A few findings, such as immature white cells called blasts, lead some labs to phone the ordering clinician right away. Most findings are mild and temporary, and a smear alone usually can't explain a condition.

What can affect your result

Infection and inflammation, which can make neutrophils look toxic or lymphocytes look reactive
Vitamin B12 and folate levels, which affect how many lobes neutrophils have
Some medicines and treatments
How long the blood sat in the tube before the smear was made
How the smear was spread and stained, which can burst fragile cells into smudge cells
The words each lab uses, which differ from lab to lab
Blood that sits in the tube for many hours before the smear is made can change how cells look. Labs set their own time limits. One hospital lab, for example, asks that a pathologist smear review be requested within 8 hours of the CBC draw.
Smudge cells are cells that burst while the smear is made, so their number can depend on how the slide was made.
Severe illness or stress, and some treatments, can change how white cells look.
Different labs use different words, so the same cells may be described differently. International recommendations try to make the wording more consistent.

Any time. The comment describes the blood sample from that draw. White cell changes can appear and fade within days as an illness starts and settles. Hypersegmented neutrophils from low vitamin B12 or folate usually clear within about 10 to 14 days of starting treatment.

When to talk to a clinician

Many findings on a blood smear are mild. A few, such as blast cells or blood parasites, are ones some labs phone to the ordering clinician right away. If your report mentions blast cells, or your lab flagged the result, contact the clinician who ordered the test soon. Contact a clinician too if you have unusual findings along with a fever that does not settle, drenching night sweats, unexplained weight loss, easy bruising or bleeding, or tiredness that is getting worse. Call 911 or your local emergency number for chest pain, severe shortness of breath, fainting or confusion.

Questions you could ask

Which white cell findings on my smear are worth following up?
How do they fit with my white cell count and differential?
Should we repeat the blood count or smear, or add tests such as vitamin B12 or folate?

Questions people ask

What are 'toxic changes' in my white cells?

Toxic changes are features in neutrophils, such as extra granules, small bubbles (vacuoles) or blue-gray patches called Döhle bodies. They are often seen when the body is responding to an infection or inflammation. Researchers have studied them in people with bacterial infections. They are a clue, not an answer, and other causes are possible. Your clinician reads them with your white cell count and symptoms.

What are reactive or atypical lymphocytes?

These are lymphocytes that look larger or more active than usual because the immune system is responding, often to a viral infection such as mononucleosis. The word 'atypical' describes how the cells look. It does not mean cancer by itself.

What are smudge cells?

Smudge cells are white cells that burst while the smear is made, leaving a smeared look. They can be seen in several conditions, including infections, and they are best known from chronic lymphocytic leukemia. Your clinician reads them together with your white cell count and the rest of your results.

Show the science and sources

For clinicians and researchers

WBC morphology is a manual or digital-image review of a stained peripheral blood film, reported as free text (LOINC 11156-7; 48705-8 combines white cells and platelets). ICSH consensus recommendations (2015) cover nomenclature and grading of abnormal white cells, red cells and platelets by manual microscopy. Smear review is typically triggered by analyzer flags or delta checks, and the criteria are set by each lab (Peripheral Smear Review Working Group, 2026). Hypersegmentation is defined as more than 5% of neutrophils with more than 5 lobes, or any neutrophil with six or more lobes. It is an early sign of megaloblastosis from vitamin B12 or folate deficiency, may come with macropolycytes, and usually clears within 10 to 14 days of starting treatment (Parakh and Dewan 2026). Toxic granulation, vacuolation and Döhle bodies were studied in 105 people with culture-confirmed bacterial infection, and toxic granulation was about as sensitive as the absolute neutrophil count for identifying infection, with band count less sensitive except in infants and older adults (Med Princ Pract 2007). Atypical lymphocytes are used in the laboratory work-up of infectious mononucleosis (Clin Infect Dis 2001), and the word 'atypical' describes how cells look, not whether they are cancerous. Smudge cells are ruptured cells formed during smear preparation. They are best known from chronic lymphocytic leukemia (Mayo Clin Proc 2007), but in a series of 102 patients they were also frequent after cardiac arrest, with infections and with other cancers (Asian Pac J Cancer Prev 2016). Some laboratories call certain smear findings urgently: the University of Chicago lists blast cells above 4% in outpatients and emergency patients, and Labcorp lists any blood parasite. Result wording varies between labs, so unrecognized phrases are treated as free text.

LOINC 11156-7 (primary), 58407-8, 48705-8. Specimen: whole-blood.

Sources

ICSH recommendations for the standardization of nomenclature and grading of peripheral blood cell morphological features, International Journal of Laboratory Hematology (2015)
Practical Considerations in the Implementation of Peripheral Smear Review in the Clinical Laboratory, International Journal of Laboratory Hematology (2026)
Blood Smear, MedlinePlus (NIH National Library of Medicine)
Peripheral Smear Review by Pathologist (test code PB Sm Path), CRMC Laboratory Test Catalog
Revisiting the hematological manifestations of vitamin B12 deficiency, Frontiers in Nutrition (2026)
The diagnostic value of absolute neutrophil count, band count and morphologic changes of neutrophils in predicting bacterial infections, Medical Principles and Practice (2007)
Using smudge cells on routine blood smears to predict clinical outcome in chronic lymphocytic leukemia: a universally available prognostic test, Mayo Clinic Proceedings (2007)
Clinical Significance of Smudge Cells in Peripheral Blood Smears in Hematological Malignancies and Other Diseases, Asian Pacific Journal of Cancer Prevention (2016)
Diagnosis of atypical cases of infectious mononucleosis, Clinical Infectious Diseases (2001)
Appendix 1: Critical Value List, The University of Chicago Medical Center Laboratories
Critical Values: critical (panic) limits with adult and pediatric reference intervals, Labcorp (2024)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.