Cystine (FMV Urine)

– High levels might be due to excessive dietary intake or impaired cystine metabolism. Converted to cysteine (reduced cystine) via a B2 and copper-dependent step. Cystine is a major component of tissue antioxidant mechanisms.

– Suspect oxidative stress if: Significantly elevated cystine, compared to cysteine (urine only)

Cystine may be low as a result of dietary protein insufficiency, malabsorption or impaired methionine metabolism. Supplementation of cystine along with antioxidant nutrients, Nacetylcysteine, or cofactors involved in methionine metabolism may be beneficial. Cystine and N-acetylcysteine supplementation should be avoided in the presence of intestinal yeast overgrowth and definitely contraindicated for insulin-dependent diabetics.

Cystine is the oxidized disulfide form of cysteine (Cys) and is the predominant form of cysteine in the blood due to its greater relative stability. Cystine is derived from dietary protein and, end formed endogenously from cysteine.