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).