73. Plasma serine to cysteine ratio as a biological marker for psychosis. Waziri R, Wilson R, Sherman AD. Abstract In a study of plasma amino acids in psychiatric patients, serine to cysteine (S/C) ratio was higher (S/C = 1.57 +/- 0.28) in 57 psychotics compared to 27 nonpsychotics (S/C = 1.06 +/- 0.23). This difference was highly significant at P less than 0.001. Psychotic patients were given a psychosis score (p score) of 1-4. The S/C ratios of individual patients were significantly correlated to their p scores (r = 0.65, P less than 0.001). S/C ratios were not related to diagnosis, age, sex, food intake and medications. When the initial S/C ratio and p scores of 22 patients were compared to their S/C ratio and p score at the time when they were improved and ready to be discharged, there was a concomitant fall both in S/C ratios and p scores suggesting the high S/C ratios may be indicative of a state rather than a trait characteristic. Our findings lead us to the conclusion that S/C ratios may provide a marker for the presence of psychosis and an index of its severity. My ratio is 4/1! tho I'm not sure if I'm comparing apples to apples since mine is a amino acid urine test. I've been taking NAC and have been feeling better. Could the cysteine be counteracting my high levels of serine?