White blood cell differential

White blood cell differential
Neutrophil (left) and lymphocytes (right) seen microscopically on a blood smear
Neutrophil (left) and lymphocytes (right) seen microscopically on a blood smear
SynonymsDifferential leukocyte count,[1] leukogram,[2] autodiff,[3] manual diff[1]
PurposeDescribing populations of white blood cells in peripheral blood
MedlinePlus003657
eMedicine2085133
LOINC33255-1, 24318-8, 69738-3

A white blood cell differential is a medical laboratory test that provides information about the types and amounts of white blood cells in a person's blood. The test, which is usually ordered as part of a complete blood count (CBC), measures the amounts of the five normal white blood cell types – neutrophils, lymphocytes, monocytes, eosinophils and basophils – as well as abnormal cell types if they are present. These results are reported as percentages and absolute values, and compared against reference ranges to determine whether the values are normal, low, or high. Changes in the amounts of white blood cells can aid in the diagnosis of many health conditions, including viral, bacterial, and parasitic infections and blood disorders such as leukemia.

White blood cell differentials may be performed by an automated analyzer – a machine designed to run laboratory tests – or manually, by examining blood smears under a microscope. The test was performed manually until white blood cell differential analyzers were introduced in the 1970s, making the automated differential possible. In the automated differential, a blood sample is loaded onto an analyzer, which samples a small volume of blood and measures various properties of white blood cells to produce a differential count. The manual differential, in which white blood cells are counted on a stained microscope slide, is now performed to investigate abnormal results from the automated differential, or upon request by the healthcare provider. The manual differential can identify cell types that are not counted by automated methods and detect clinically significant changes in the appearance of white blood cells.

In 1674, Antonie van Leeuwenhoek published the first microscopic observations of blood cells. Improvements in microscope technology throughout the 18th and 19th centuries allowed the three cellular components of blood to be identified and counted. In the 1870s, Paul Ehrlich invented a staining technique that could differentiate between each type of white blood cell. Dmitri Leonidovich Romanowsky later modified Ehrlich's stain to produce a wider range of colours, creating the Romanowsky stain, which is still used to stain blood smears for manual differentials.

Automation of the white blood cell differential began with the invention of the Coulter counter, the first automated hematology analyzer, in the early 1950s. This machine used electrical impedance measurements to count cells and determine their sizes, allowing white and red blood cells to be enumerated. In the 1970s, two techniques were developed for performing automated differential counts: digital image processing of microscope slides and flow cytometry techniques using light scattering and cell staining. These methods remain in use on modern hematology analyzers.

Example of WBC differential reference ranges[4]
Cell type Adult
reference range
(× 109/L) 		Adult
reference range
(percentage)
Neutrophils 1.7–7.5 50–70
Lymphocytes 1.0–3.2 18–42
Monocytes 0.1–1.3 2–11
Eosinophils 0.0–0.3 1–3
Basophils 0.0–0.2 0–2

The white blood cell differential is a common blood test that is often ordered alongside a complete blood count. The test may be performed as part of a routine medical examination; to investigate certain symptoms, particularly those suggestive of infection or hematological disorders;[5][6] or to monitor existing conditions, such as blood disorders and inflammatory diseases.[7]

Five types of white blood cells are normally found in blood: neutrophils, lymphocytes, monocytes, eosinophils and basophils.[8] Marked shifts in the proportions of these cell types, as measured by the automated or manual differential, can indicate various health conditions.[9] Additionally, cell types which do not normally occur in the blood, such as blast cells, can be identified by the manual differential. These cell types may be found in blood disorders and other pathological states.[10][11] The manual differential can also identify changes in the appearance of white blood cells, such as reactive lymphocytes,[12] or features such as toxic granulation and vacuolation in neutrophils.[13] The results of the white blood cell differential are reported as percentages and absolute values. Absolute counts are usually reported in units of cells per microliter (μL) or 109 cells per liter (L).[6] The result are then compared against reference ranges, which are defined by individual laboratories and may vary due to different patient populations and testing methods.[14]

CBC and differential testing is usually performed on venous or capillary blood. Capillary blood draws are generally used for infants and individuals whose veins are difficult to access.[15] To prevent clotting, the sample is drawn into a tube containing the anticoagulant compound ethylenediaminetetraacetic acid (EDTA).[16], meaning blood that has not been centrifuged.[17]

  1. ^ a b Cite error: The named reference GulatiSong2013 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference ecli_Leuk was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference Lutinger2002 was invoked but never defined (see the help page).
  4. ^ Keohane, Smith & Walenga 2015, Front matter
  5. ^ Cite error: The named reference medline was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference LTO was invoked but never defined (see the help page).
  7. ^ Kottke-Marchant & Davis 2012, p. 33
  8. ^ Turgeon 2016, p. 303
  9. ^ Cite error: The named reference BarnesMcfadden2005 was invoked but never defined (see the help page).
  10. ^ d'Onofrio & Zini 2014, p. 289
  11. ^ Cite error: The named reference Chabot-Richards2015 was invoked but never defined (see the help page).
  12. ^ Bain, Bates & Laffan 2012, pp. 95–7
  13. ^ Ciesla 2018, p. 153
  14. ^ Cite error: The named reference ICSH2015 was invoked but never defined (see the help page).
  15. ^ Bain, Bates & Laffan 2012, pp. 2–4
  16. ^ Smock, KJ in Greer et al. 2018, Ch. 1 § Specimen collection
  17. ^ Warekois & Robinson 2013, p. 116