The stability of 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid in human urine.

5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid are important intermediate metabolites in the formation of cutaneous melanin pigment. Since they both are serious candidates as markers of melanoma progression, their stability in urine has been investigated during storage at various conditions. The results show that storage at -20 degrees C is necessary. Both compounds are nonstable at room temperature, particularly if the urine was not acidified to pH 4-5. Reference levels were obtained from analysis of urine from 31 men and 40 women. The mean (SD) excretion of 5-S-cysteinyldopa was 32 (12.5) mumol/mol creatinine (women). Corresponding figures for 6H5MI2C were 23 (10.3) and 24 (8.1) mumol/mol creatinine for men and women respectively.