Leukocytosis: A transient increase in the number of leukocytes in a body fluid.Leukemoid Reaction: A peripheral blood picture resembling that of leukemia or indistinguishable from it on the basis of morphologic appearance alone. (Dorland, 27th ed)Leukocyte Count: The number of WHITE BLOOD CELLS per unit volume in venous BLOOD. A differential leukocyte count measures the relative numbers of the different types of white cells.Paraneoplastic Syndromes: In patients with neoplastic diseases a wide variety of clinical pictures which are indirect and usually remote effects produced by tumor cell metabolites or other products.Thrombocytosis: Increased numbers of platelets in the peripheral blood. (Dorland, 27th ed)Thrombocythemia, Essential: A clinical syndrome characterized by repeated spontaneous hemorrhages and a remarkable increase in the number of circulating platelets.Polycythemia Vera: A myeloproliferative disorder of unknown etiology, characterized by abnormal proliferation of all hematopoietic bone marrow elements and an absolute increase in red cell mass and total blood volume, associated frequently with splenomegaly, leukocytosis, and thrombocythemia. Hematopoiesis is also reactive in extramedullary sites (liver and spleen). In time myelofibrosis occurs.Hypercalcemia: Abnormally high level of calcium in the blood.Splenomegaly: Enlargement of the spleen.Lymphocytosis: Excess of normal lymphocytes in the blood or in any effusion.Myeloproliferative Disorders: Conditions which cause proliferation of hemopoietically active tissue or of tissue which has embryonic hemopoietic potential. They all involve dysregulation of multipotent MYELOID PROGENITOR CELLS, most often caused by a mutation in the JAK2 PROTEIN TYROSINE KINASE.Granulocyte Colony-Stimulating Factor: A glycoprotein of MW 25 kDa containing internal disulfide bonds. It induces the survival, proliferation, and differentiation of neutrophilic granulocyte precursor cells and functionally activates mature blood neutrophils. Among the family of colony-stimulating factors, G-CSF is the most potent inducer of terminal differentiation to granulocytes and macrophages of leukemic myeloid cell lines.Anemia, Myelophthisic: Anemia characterized by appearance of immature myeloid and nucleated erythrocytes in the peripheral blood, resulting from infiltration of the bone marrow by foreign or abnormal tissue.Leukocytes: White blood cells. These include granular leukocytes (BASOPHILS; EOSINOPHILS; and NEUTROPHILS) as well as non-granular leukocytes (LYMPHOCYTES and MONOCYTES).Selectins: Transmembrane proteins consisting of a lectin-like domain, an epidermal growth factor-like domain, and a variable number of domains that are homologous to complement regulatory proteins. They are important cell adhesion molecules which help LEUKOCYTES attach to VASCULAR ENDOTHELIUM.Diverticulitis, Colonic: Inflammation of the COLONIC DIVERTICULA, generally with abscess formation and subsequent perforation.Fatal Outcome: Death resulting from the presence of a disease in an individual, as shown by a single case report or a limited number of patients. This should be differentiated from DEATH, the physiological cessation of life and from MORTALITY, an epidemiological or statistical concept.Bordetella pertussis: A species of gram-negative, aerobic bacteria that is the causative agent of WHOOPING COUGH. Its cells are minute coccobacilli that are surrounded by a slime sheath.Neutrophils: Granular leukocytes having a nucleus with three to five lobes connected by slender threads of chromatin, and cytoplasm containing fine inconspicuous granules and stainable by neutral dyes.Primary Myelofibrosis: A de novo myeloproliferation arising from an abnormal stem cell. It is characterized by the replacement of bone marrow by fibrous tissue, a process that is mediated by CYTOKINES arising from the abnormal clone.Fever: An abnormal elevation of body temperature, usually as a result of a pathologic process.Sweet Syndrome: Condition characterized by large, rapidly extending, erythematous, tender plaques on the upper body usually accompanied by fever and dermal infiltration of neutrophilic leukocytes. It occurs mostly in middle-aged women, is often preceded by an upper respiratory infection, and clinically resembles ERYTHEMA MULTIFORME. Sweet syndrome is associated with LEUKEMIA.Oxides: Binary compounds of oxygen containing the anion O(2-). The anion combines with metals to form alkaline oxides and non-metals to form acidic oxides.Platelet Count: The number of PLATELETS per unit volume in a sample of venous BLOOD.Blood Cell Count: The number of LEUKOCYTES and ERYTHROCYTES per unit volume in a sample of venous BLOOD. A complete blood count (CBC) also includes measurement of the HEMOGLOBIN; HEMATOCRIT; and ERYTHROCYTE INDICES.