Objective: Lithium and valproic acid are drugs used in psychiatric and neurological disorders. Accurately measurements of serum levels of these drugs are important due to the narrowness of therapeutic range and rather wide side effect of these drugs. Analyze of samples may be delayed due to technical problems in the laboratory or in the process of samples delivery to the laboratory. If the problem can not be resolved in the same day, refrigerator waiting period may extend. It is known that prolonged storage time and inappropriate temperature may cause incorrect results for many analyses. In our study, we aimed to investigate the effects of storage temperature and time on the stability of lithium and total valproic acid levels.

Materials and Methods: Blood samples were collected from patients who are taking lithium (n=15) and valproic acid (n=15). Serum samples were separated into 3 parts. The first part was analyzed immediately and stored 24 hours at room temperature (24°C -26°C) and then reanalyzed. The second part was stored at +4°C and were analyzed at 24th and 48th hours. The third part of samples was analyzed after stored at -20°C in a freezer for 1 month.

Results: The difference of lithium levels between the measurements at baseline and stored at -20°C for 1 month (p=0.003) ( percent change %14.28) and stored at room temperature for 1 day (p=0.001) ( percent change %47.14), were statistically significant. Valproic acid results between the measurements at baseline and stored at -20°C for 1 month were statistically significant (p=0.015) (percent change %15.78). There was not any significant difference between the other results.

Conclusions: Serum samples for lithium measurement should be analyzed immediately or can be stored at +4°C for two days. But the samples should not be stored at -20°C, or at room temperature. However the serum samples for valproic acid measurement can be stored at room temperature for 1 day or at +4°C for two days. But they should not be stored at -20°C.