Hydroxyurea interferes negatively with triglyceride measurement by a glycerol oxidase method

Measured triglyceride concentrations were extremely low (less than 100 mg/L) in the serum of some patients who were receiving hydroxyurea for myeloproliferative diseases. The assay being used to quantify triglycerides was a "cascaded" enzymatic method involving (a) lipase, to generate glycerol from triglycerides; (b) glycerol oxidase, to convert glycerol to glyceraldehyde, with generation of hydrogen peroxide; and (c) peroxidase, which acts on the hydrogen peroxide with subsequent coupled generation of a red-violet quinone (reagent system used in the Technicon RA-1000). Hydroxyurea added to serum samples appeared to inhibit the action of glycerol oxidase, with a stoichiometric relation to the concentration of substrate (a decrease of roughly 2.4 mmol/L in measured triglyceride per 1 mmol of hydroxyurea per liter). A different enzymatic assay for triglycerides, which involves glycerol kinase (Beckman Instruments) did not show this effect of hydroxyurea.