(1) Given my knowledge of the CBC diff is as hazy as this tropical storm coming through NYC, here’s a @medtweetorial breaking it down! All info comes from Wash. Manual’s Heme/Onc Consult book.
(2) Let’s start w/ high cell counts by considering leukocytosis, defined as WBC >10 x10^9 cells/L. Generally speaking, we’re all familiar with leukocytosis most commonly being a marrow response to inflammation/infection. This response is rapid due to marrow/vessel demargination!
(3) With a leukocytosis, you can take the %-cell-count and multiply together to determine the presence of neutrophilia, eosinophilia, basophilia, monocytosis, & lymphocytosis via the resultant absolute-cell-count.
(4) NEUTROPHILIA is defined as an absolute neutrophil count (ANC) >6.6 x10^9 cells/L. The first step in this w/u is to acquire a smear to confirm the count & r/o spurious leukocytosis (ie the counting of plt clumps).
(5) Neutrophilia may be primary/secondary. Generally, can consider first secondary causes since they are by far the most common causes. In neutrophilia, consider infection, chronic inflammatory dz, smoking (25% inc.), meds (steroids), & marrow infiltration/stimulation.
(6) In eval for secondary causes, the smear may provide clues. Bands, vacuolization, Dohle bodies, & toxic granulations suggest secondary etiologies such as inflammation/infection. The classic “leukoerythroblastic rxn” suggests marrow infiltration. Blasts suggest acute leukemia.
(7) EOSINOPHILIA is defined as absolute eos. count >0.5 x10^9 cells/L. Although most commonly due to allergy/derm condition, a can’t miss item on the DDx is adrenal insufficiency. The DDx also includes parasitic infxn, HIV, autoimmunity, & pleural/lung pathology (eg Loffler’s).
(8) A complete w/u of eosinophilia includes a smear, stool O&P, serum tryptase (to test for mast cell activation & mastocytosis), cortisol (to r/o adrenal insuff.), IgE, & IL-5.
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(9) Does your eosinophilic patient have a cardiac conduction defect or cardiomyopathy? Is eos. count >4 x10^9 cells/L? If so, consider Hypereosinophilic syndrome, a rare primary cause! Rx – steroids & hydroxyurea.
(10) BASOPHILIA is defined as an absolute basophil count >0.2 x10^9 cells/L. Unlike neutrophilia/eosinophilia with secondary etiologies being the most common culprits, the most common cause of basophilia is a myeloproliferative disorder (eg CML).
(11) Given basophils’ major function is to activate Type I hypersens. rxns through surface receptors for IgE, basophilia may also be more rarely due to a hypersens. rxn. Basophilia may also be more rarely seen in chronic inflammatory states.
(12) Finally, LYMPHOCYTOSIS is defined as an absolute lymphocyte count >3.3 x10^9 cells/L. Although commonly reactive to a mono-syndrome or one of the 3-lettered viruses (EBV/CMV/HSV/HIV), lymphocytosis also raises suspicion for malignancy.
(13) The smear is a helpful guide for the DDx. Reactive lymphocytes? Think infection. Smudge cells? CLL. Blasts? Acute leukemia. Cell surface markers are also sent to distinguish primary/secondary lymphocytosis.
(14) Alright, let’s go to low cell counts. Leukopenia is defined as WBC <3.8 x10^9 cells/L. It is divided into neutropenia & lymphopenia. Again, find your absolute neutrophil & lymphocyte counts by multiplying %-cell-count against your WBC count.
(15) NEUTROPENIA is defined as mild if ANC 1-1.5, moderate if ANC 0.5-1, & severe if ANC <0.5 x10^9 cells/L. Although risk of infxn increases at <1.0, patients are usually asx until <0.5. The risk of infxn is related to the degree/duration of neutropenia.
(16) Actually, neutropenia is often found incidentally. Signs of infection (eg purulence) are less evident given low ANC. However, fever possible. First, consider primary causes, including leukemia/lymphoma c/b marrow crowding, aplastic anemia, & nutritional deficiency.
(17) Secondary causes of neutropenia include sepsis, viral infxn (EBV, parvovirus, HIV), drug-induced, autoimmunity, marrow infiltration, & hypersplenism. A good history will elucidate any recent infection or new drug.
(18) A good physical for neutropenia includes oral exam (looking for infxn/gingivitis, macroglossia supportive of nutritional deficiency), LN exam (for malignancy), skin/joint exam (for autoimmunity), & splenic exam (for splenic sequestration).
(19) Neutropenic w/u may include HIV/EBV serologies, marrow asp. for pancytopenia, serial CBC to r/o a rare primary cause called cyclic neutropenia, folate/B12/Cu, & ANA/ANCAs for autoimmunity. If ill/febrile, start empiric abx until ANC >500/L for 2 days & until defervescence.
(20) LYMPHOPENIA is defined as an absolute lymphocyte count <1.2 x10^9 cells/L. It's usually acquired and should always prompt consideration of HIV. Other infectious causes include viruses, tick-born dz, sepsis malaria, & TB.
(21) Remaining secondary causes include autoimmunity, sarcoidosis, ETOH abuse, & Zn deficiency.
And that's about it! Inspiration from @smalltownOMS's recent tweetorial on leishmaniasis! @MedTweetorials
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