HA: Hemagglutination.

HAA: Hepatitis-associated antigen.

HAI: Hemagglutination inhibition.

Habitat: The natural environment/area/location in which where an organism normally grows.

Hallucinosis: A syndrome characterized by hallucinations that are caused by organic substances such as drugs and alcohol.

Halophile: An organism requiring salt (NaCl) for growth.

Halophilic: Growing best at high NaCl concentrations.

Halotolerant: An organism capable of growing in the presence of NaCl but not requiring it.

Halzoun: Presence of worms on pharyngeal mucosa; congestion of tissues accompanied by difficulty in breathing and possible asphyxiation (Fasciola hepatica and pentastome infections).

Haploid: Having n or reduced number of chromosomes.

Hapten: A substance not inducing antibody formation but able to combine with a specific antibody.

Harada-Mori culture: Method of incubating fecal material on a filter paper strip in a test tube containing water (cover one-third of the length of the paper strip) for the purpose of culturing and recovering nematode larvae (Strongyloides stercoralis, hookworm).

HATTS: The hemagglutination treponemal test for syphilis.

Hb; Hgb: Hemoglobin.

HBV: Hepatitus B virus.

HCHO: Formaldehyde.

HCl: Hydrochloric acid.

HCT: Hematocrit.

HCW: Healthcare worker.

HD: Hemodialysis.

Headspace gas: Gas generated during growth of an organism in a closed tube that accumulates between the upper surface of the broth in the tube and the top of the tube.

Helical: Curved in three dimension and having one or more turns; corkscrew-shaped.

Helix: A spiral structure in a macromolecule that contains a repeating pattern.

Helminth: May refer to a nematode (roundworm), cestode (tapeworm), or trematode (fluke).