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Medical Dictionary     H
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  • H
    Symbol for Planck constant; Hill coefficient.
  • H agglutinin
    an agglutinin that is formed as the result of stimulation by, and which reacts with, the thermolabile antigen(s) in the flagella of motile strains of microorganisms; See ABO blood group, Blood Groups Appendix.

    Alternate names: flagellar agglutinin

  • H and H

    H and H: H and H, sometimes written as "H&H", is a popular shorthand for hemoglobin and hematocrit, two very common and important blood tests. Hemoglobin is the oxygen-carrying protein pigment in the blood, specifically in the red blood cells. In the test for hemoglobin (Hb), it is usually measured as total hemoglobin expressed as the amount of hemoglobin in grams (gm) per deciliter (dl) of whole blood, a deciliter being 100 milliliters. The normal ranges for hemoglobin depend on the age and, beginning in adolescence, the sex of the person. The normal ranges are: Newborns: 17-22 gm/dl One (1) week of age: 15-20 gm/dl One (1) month of age: 11-15gm/dl Children: 11-13 gm/dl Adult males: 14-18 gm/dl Adult women: 12-16 gm/dl Men after middle age: 12.4-14.9 gm/dl Women after middle age: 11.7-13.8 gm/dl All of these values may vary slightly between laboratories. Some laboratories do not differentiate between adult and "after middle age" hemoglobin values. The hematocrit is the proportion, by volume, of the blood that consists of red blood cells. The hematocrit (hct) is expressed as a percentage. For example, an hematocrit of 25% means that there are 25 milliliters of red blood cells in 100 milliliters of blood: a quarter of the blood consists of red cells. The normal ranges for hematocrit are dependant on age and, after adolescence, sex. The normal ranges are: Newborns: 55-68% One (1) week of age: 47-65% One (1) month of age: 37-49% Three (3) months of age: 30-36% One (1) year of age: 29-41% Ten (10) years of age: 36-40% Adult males: 42-54% Adult women: 38-46% These values may vary slightly between laboratories.

  • H antigen
    the antigen in the flagella of motile bacteria; important in serologic classification of enteric bacteria. the chemical precursor of antigens of the ABO blood group locus.

    See Also: O antigen1

  • H band
    the paler area in the center of the A band of a striated muscle fiber, comprising the central portion of thick (myosin) filaments that are not overlapped by thin (actin) filaments.

    Alternate names: H disc, Hensen disc, Hensen line

  • H colony
    a colony of motile organisms forming a thin film of growth.
  • H rays
    a stream of hydrogen nuclei; protons.
  • H reflex
    a monosynaptic reflex consistently obtained in normal adults only by electrically stimulating the tibial nerve, generally in the popliteal fossa, while recording from the gastrocnemius-soleus muscle group; similar to the clinically elicited Achilles reflex, except that the neuromuscular spindles are bypassed. Widely used in the EMG laboratory to diagnose S1 radiculopathies and polyneuropathies.
  • H shunt
    a side-to-side shunt between adjacent vessels that uses a connecting conduit; this shunt is most commonly placed between the superior mesentary vein and the inferior vena cava in patients with portal hypertension.

    Alternate names: H graft

  • H substance
    designation given by Thomas Lewis to a diffusible substance in skin, indistinguishable in action from histamine, liberated by injury and causes the triple response.

    Alternate names: released substance

  • Häser formula
    a formula to determine the number of grams of urinary solids per liter, obtained by multiplying 2.33 by the last two figures of the specific gravity of the urine.

    Alternate names: Christison formula, Trapp formula, Trapp-Häser formula


  • Symbol for photon, and represents photon energy, where h = Planck's constant and ν = frequency of electromagnetic wave.
  • Hückel rule
    the number of depolarized electrons in an aromatic ring is equal to 4n + 2 where n is 0 or any positive integer; l-tyrosine, l-phenylalanine, l-tryptophan, and l-histidine (when the imidazole ring is deprotonated) obey this rule.
  • Hüfner equation
    an equation expressing the relationship between myoglobin dissociation and oxygen partial pressure: ([MBO2]/[Mb]) = (K × pO2).
  • Hürthle cell
    a large, granular eosinophilic cell derived from thyroid follicular epithelium by accumulation of mitochondria, in Hashimoto disease.

    Alternate names: Askanazy cell

  • Hürthle cell adenoma
    an uncommon type of thyroid tumor characterized by abundant eosinophilic cytoplasm containing numerous mitochondria. Often malignant with widespread metastases; rarely takes up radioiodine.

    Alternate names: oncocytic adenoma

    See Also: Hürthle cell carcinoma

  • Hürthle cell carcinoma
    a salivary or thyroid carcinoma composed of cells that have eosinophilic cytoplasm.

    Alternate names: oncocytic carcinoma, oxyphilic carcinoma

    See Also: Hürthle cell adenoma

  • H+
    Symbol for Planck constant; Hill coefficient.
  • H-2 antigens
    antigens that are coded by the H-2 complex of genes in mice and are involved in self/nonself recognition. H-2 antigen system is analogous to HLA.
  • H-2 complex
    term that denotes genes of the major histocompatibility complex in the mouse.
  • H-ficolin
    also known as Hakata antigen or ficolin3, structurally resembles mannose-binding lectin (MBL). The polypeptide chains have a N-terminal region, a collagenlike domain and a globular region, which is fibrinogenlike. H-ficolin is a plasma protein generated in the liver. H-ficolin can form oligomers and is capable of activating complement.

    See Also: ficolin, L-ficolin

  • H-meromyosin
    one of the relatively heavy products (mol. wt. about 350,000) of the action of trypsin on myosin; it carries the ATPase activity of myosin.
  • H-shape vertebrae
    sharply delimited depression of the central portion of the endplates of the vertebrae, producing a stocky “H” shape on radiographs, as in sickle cell anemia.
  • H-type fistula
    a rare form of congenital tracheoesophageal fistula in which there is no esophageal atresia; manifest as aspiration pneumonias.

    Alternate names: H-type tracheoesophageal fistula

  • H-Y antigen
    an antigen factor, dependent on the Y chromosome, responsible for the differentiation of the human embryo into the male phenotype by inducing the initially bipotential embryonic gonad to develop into a testis; in the absence of this antigen, the indifferent gonad develops into an ovary. There are at least two loci involved, an autosomal gene that generates the antigen [MIM*143170] and one that makes the receptor [MIM*143150].
  • H. flu

    H. flu: See Haemophilus influenzae type b.

  • H. flu immunization

    H. flu immunization: See HIB immunization.

  • H. heilmannii

    H. heilmannii: Short for Helicobacter heilmannii, a bacteria that infects most cats, dogs and pigs and, in them, causes stomach inflammation (gastritis). H. heilmannii is not usually transmitted from animals to people. But people who have been infected by H. heilmannii are known to have developed gastric ulcers. Antibiotics can cure H. heilmannii infections.

  • h.d.
    Abbreviation for L. hora decubitus, at bedtime.
  • h.r.a.
    Abbreviation for health risk assessment.
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