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Definition of Histidine

Medically reviewed by Min Clinic Staff | Updated: January 2026

Histidine: An amino acid, one of the 20 building blocks of protein. An essential amino acid, histidine is present in many proteins. Histidine is elevated in the blood and urine in a genetic condition called histidinemia. Decarboxylation of histidine results in the formation of histamine. Symbol: His.