Definition of "Leukocytosis"
Leukocytosis is WBC count above the normal range in blood.
Patient information
What is leukocytosis?Leukocyte is another word for white blood cells, and "-osis" means an abnormal state. Specifically, it's when it's elevated.
What's low white blood cells then?
Leukopenia. "-penia" means deficiency, and is where we get our word "poverty" from.
Coolbeans. So, wait, what are white blood cells?
White blood cells help to protect our body against infectious disease and foreign invaders. Although it only makes up 1% of blood, it's important because our immunity depends on it.
- Neutrophilia (neutrophilic leukocytosis), the most common form, which is caused by:
- Acute bacterial infections, especially pyogenic infections
- Sterile inflammation, including tissue necrosis, including myocardial infarction, burns
- Lymphocytosis, including:
- Chronic infections, including TB (tuberculosis), brucellosis
- Viral infections, including hepatitis, CMV infection (cytomegalovirus), infectious mononucleosis
- Pertussis
- Some forms of malignancy, e.g. lymphocytic leukemias
- Monocytosis, including:
- Chronic infections, including TB (tuberculosis), bacterial endocarditis, rickettsiosis, malaria
- Systemic autoimmune diseases, e.g. SLE
- Inflammatory bowel diseases, e.g. UC
- Eosinophilia (eosinophilic leukocytosis), caused by:
- Allergic disorders, including asthma, hayfever, drug allergies, allergic skin diseases (pemphigus, dermatitis herpetiformis)
- Parasitic infections
- Some forms of malignancy, including Hodgkin's lymphoma, some forms of non-Hodgkin lymphoma
- Systemic autoimmune disease, e.g. SLE
- Some forms of vasculitis
- Cholesterol embolism, transiently
- Basophilia (basophilic leukocytosis), which is rare, including:
- Myeloproliferative disease, e.g. CML (chronic myelogenous leukemia
Patient information
So what can cause elevated white blood cells?So we divide it into different types, because there are 5 different types of white blood cells, neutrophils (62%), lymphocytes (30%), monocytes (5.3%), eosinophils (2.3%), and basophils (0.4%). So each of them look different under a microscope, and have different life spans. Their key conceptual difference though, is in their targets. Neutrophils target bacteria and fungi. Lymphocytes are divided into your B, T, and natural killer cells. Monocytes migrate to other tissue and differentiate into macrophages. Eosinophils target parasites and helps modulate the allergic response. Basophils release histamine for an inflammatory response.
So elevated neutrophils is when you're targetting bacteria and fungi?
Yep, so bacterial is a biggy. But because neutrophils are the most abundant, you'll also see it even in generalized non-infectious inflammation.
Elevated lymphocytes would mean more B, T, and natural killer cells. Wait, what are they for?
B cells mature in the bone marrow, and make antibodies. T cells mature in the thymus, and there are various types, including CD4+ helper cells that work with various other immune cells, CD8+ cytotoxic cells that destroy virus infected and tumor cells, and memory cells that memorize past infections. Natural killer cells is the non-adaptive (which we call innate) version of the cytotoxic T cells. So here we're talking long term infections, viral infections, and cancers.
Elevated monocytes would mean more macrophages. Wait, oh man... this is so complicated 
... what's that?
Macrophages are cells that engulf and digest... well, just about all bad stuff, whether it be cellular debris, foreign substances, microbes, cancer cells. They do this in a process called phagocytosis. As you'd expect, their use is quite broad.
Elevated eosinophils would be in allergic diseases?
Yep, that's the biggy, so asthma, hay fever, drug allergies, allergic skin diseases.
Elevated basophils would be... again, allergies?
Well that's rare, actually.
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