What is a differential count?

Differential white cell count (or differential count) is a sub-classification of white blood cells giving the absolute numbers and relative proportions of each type of white blood cell, including neutrophils, lymphocytes, monocytes, eosinophils and basophils. This helps to characterise the most likely causes of a raised or low white cell count.

How is a differential count performed?

Differential white cell count is a blood test performed as a routine part of the Full Blood Count (FBC). It is a blood test.

When would you need a differential count?

The differential white cell count is part of the routine information provided by a full blood count (FBC), which includes as one of its components the white cell count (WCC). Your doctor may pay particular attention to the ‘diff count’ when there is a suspicion of infection, or when the WCC is particularly high or low – to find out which particular types of white cell are increased or decreased.

Why should one get white cell count tested?

The white blood cell (WBC) count alludes to the presence of illness because these cells are made in the bone marrow and protect the body against infection. They play a key role in the body's immune response, so if an infection is present, these cells will kick into play to attack and destroy the bacteria.

What are some seemingly routine things that can cause alterations in white blood cell levels?

It's interesting but normal things like eating, strenuous physical activity, and even stress can cause an elevated WBC count. Pregnant women in their final month and labour may also be associated with increased WBC levels.

Differential count results explained

The differential white cell count is most useful in the setting of a high or low total WCC.

When the WCC is high, the particular proportions of white-cell subtypes may be suggestive of:

  • Infection – raised neutrophils
  • Specific infections – raised lymphocytes may be found in Infectious Mononucleosis, other viral infections, tuberculosis, some fungal infections, or longstanding bacterial infections
  • Allergy – raised eosinophil count

The appearance of the cells under a microscope may also give clues, for example:

  • ‘Leftward shift’ in neutrophils (appearance of less mature forms) suggests infection, particularly bacterial
  • ‘Atypical lymphocytes’ suggests infectious mononucleosis (glandular fever)
  • ‘Blasts’are very immature forms of white cells which suggests (but does not confirm) one of several types of leukaemia

In the setting of a LOW or normal total WCC:

  • Low lymphocyte count suggests viral infection
  • Low neutrophil count (neutropaenia) may be due to an acute infection, or may be in the setting of recent chemotherapy, a potentially dangerous situation where the risk of serious infection is increased.

Related specialists

Related procedures

  • Blood Test (venesection)
  • Bone Marrow Biopsy

Related tests

Also known as

  • Differential WBC / WCC
  • Differential count
  • Diff count


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