The patients with pruritus had elevated plasma histamine concentrations ( 20.7 + / - 2.7 nmol per liter ) , as compared with the patients without pruritus ( 4.2 + / - 0.6 nmol per liter ; P less than 0.001 ) and normal subjects ( 2.1 + / - 0.2 nmol per liter ; P less than 0.001 ) .
