WordNet

(mechanics) the equal and opposite force that is produced when any force is applied to a body; "every action has an equal and opposite reaction"
a response that reveals a persons feelings or attitude; "he was pleased by the audiences reaction to his performance"; "John feared his mothers reaction when she saw the broken lamp"
a bodily process occurring due to the effect of some antecedent stimulus or agent; "a bad reaction to the medicine"; "his responses have slowed with age" (同)response
doing something in opposition to another way of doing it that you dont like; "his style of painting was a reaction against cubism"
an idea evoked by some experience; "his reaction to the news was to start planning what to do"
extreme conservatism in political or social matters; "the forces of reaction carried the election"

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{名}(…に対する)『反応』《+『to』+『名』》 / 〈U〉(…に対する)(政治的・社会的な)『反動』,逆コース《+『against』+『名』》 / 〈U〉〈C〉化学反応,化学変化 / 〈U〉〈C〉(物理学で)反作用

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/05/08 15:20:51」(JST)

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The term leukemoid reaction describes an increased white blood cell count, or leukocytosis, which is a physiological response to stress or infection (as opposed to a primary blood malignancy, such as leukemia).

It may be lymphoid or myeloid.^[1]

Definition and diagnosis

Conventionally, a leukocytosis exceeding 50,000 WBC/mm³ with a significant increase in early neutrophil precursors is referred to as a leukemoid reaction.^[2] The peripheral blood smear may show myelocytes, metamyelocytes, promyelocytes, and rarely myeloblasts; however, there is a mix of early mature neutrophil precursors, in contrast to the immature forms typically seen in acute leukemia. Serum leukocyte alkaline phosphatase is normal or elevated in leukemoid reaction, but is depressed in chronic myelogenous leukemia. The bone marrow in a leukemoid reaction, if examined, may be hypercellular but is otherwise typically unremarkable.

Leukemoid reactions are generally benign and are not dangerous in and of themselves, although they are often a response to a significant disease state (see Causes below). However, leukemoid reactions can resemble more serious conditions such as chronic myelogenous leukemia (CML), which can present with identical findings on peripheral blood smear.

Historically, various clues including the leukocyte alkaline phosphatase score and the presence of basophilia were used to distinguish CML from a leukemoid reaction. However, at present the test of choice in adults to distinguish CML is an assay for the presence of the Philadelphia chromosome, either via cytogenetics and FISH, or via PCR for the BCR/ABL fusion gene. The LAP (Leukocyte Alkaline Phosphatase) score is high in reactive states but is low in CML. In cases where the diagnosis is uncertain, a qualified hematologist or oncologist should be consulted.

Causes of leukemoid reaction

As noted above, a leukemoid reaction is typically a response to an underlying medical issue. Causes of leukemoid reactions include:

Hemorrhage
Drugs
- Use of Sulfa drugs
- Use of Dapsone
- Use of glucocorticoids
- Use of G-CSF or related growth factors
- All-trans retinoic acid (ATRA)
Infections
- Clostridium difficile
- Tuberculosis
- Pertussis
- Infectious mononucleosis (lymphocyte predominant)
- Visceral Larva Migrans (eosinophil predominant)
Asplenia
Diabetic ketoacidosis
Organ necrosis
- Hepatic necrosis
- Ischemic colitis
As a feature of Trisomy 21 in infancy (incidence of ~10%)
As a paraneoplastic phenomenon (rare)

References

^ Ian M. Hann; Owen P. Smith (26 September 2006). Pediatric hematology. Wiley-Blackwell. pp. 763–. ISBN 978-1-4051-3400-2. Retrieved 5 November 2010.
^ Ronald Hoffman et al. (2005). Hematology: basic principles and practice. St. Louis, Mo: Elsevier Churchill Livingstone. ISBN 0-443-06628-0. p. 803.

UpToDate Contents

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1. 好中球増多症の原因 causes of neutrophilia
2. 好中球増多症の患者へのアプローチ approach to the patient with neutrophilia
3. 血液悪性腫瘍における白血球増多症および白血球症 hyperleukocytosis and leukostasis in hematologic malignancies
4. 慢性骨髄性白血病の臨床症状および診断 clinical manifestations and diagnosis of chronic myeloid leukemia
5. クロストリジウム・ソルデリによる毒素性ショック症候群 toxic shock syndrome due to clostridium sordellii

English Journal

A leukemoid leucocytosis.

Cherif E, Kechaou I, Hassine LB, Boukhris I, Azzabi S, Kaouech Z, Kooli C, Khalfallah N.SourceService de médecine interne B, Hôpital Charles Nicolle, Tunis, Tunisie.
Annales de biologie clinique.Ann Biol Clin (Paris).2012 Jun 1;70(3):333-334.
Leukemoid reaction is a rare paraneoplastic syndrome. It can occur in association with carcinomas, in particular of the lung, gastric and renal. However, its association with sarcoma is infrequent. Leukemoid reaction occuring in patients with uterine sarcoma have not been previously reported. We rep
PMID 22565182

Hyperleukocytosis in a premature infant with intrauterine herpes simplex encephalitis.

Underwood MA, Wartell AE, Borghese RA.SourceDepartment of Pediatrics, University of California, Davis School of Medicine, Sacramento, CA, USA.
Journal of perinatology : official journal of the California Perinatal Association.J Perinatol.2012 Jun;32(6):469-72. doi: 10.1038/jp.2011.138.
Herpes encephalitis is a rare but devastating infection in premature infants. We report a 29 week gestation infant with severe intrauterine cutaneous and central nervous system herpes accompanied by hyperleukocytosis. Leukemoid reactions are not uncommon in this population, but the association of he
PMID 22643292