Abstract:

Objective To study the role of different concentrations of betaine on serum lactate dehydrogenase（LDH） stability at different storage temperatures（2-8 ℃,-20 ℃）. Methods The 5 mol/L betaine was added to serum samples at different ratios. No betaine was added to the samples in group 1. The ratios of betaine to sample（V∶V） were 9∶1,8∶2,7.5∶2.5 and 6∶4 for the samples in groups 2 to 5,respectively. Betaine concentration was 0.5-1.25 mol/L. All serum samples were determined for total LDH activity and LDH isoenzyme electrophoresis analysis before storage,and the results of this assay were used as baseline values. The total LDH activity and the percentage of isoenzymes were determined after storage at 2-8 ℃ and -20 ℃ for different times,respectively,and the differences from the baseline values were calculated. Results The recoveries of total LDH activity for serum samples in groups 2 to 4 ranged from 98.36% to 101.41%,and 95.16%-103.48% for serum samples in group 5. Among them,1 serum sample had an offset higher than the deviation specified in the Chinese health industry standard WS/T 403—2012（4.0%）. Under 2-8 ℃ storage for 30 d,the total LDH activity of serum samples in group 1 was 52.31%-59.95% of the baseline value. The total LDH activities of serum samples in groups 2 to 4 were 98.54%-101.64% of the baseline value,and the results were stable. The total LDH activity of serum samples in group 1 was 88.78%-91.57% of the baseline value when stored at -20 ℃ for 21 d. The total LDH activities of serum samples in groups 2 to 4 were 56.14%-65.34% of the baseline value. The proportions of LDH1 and LDH2 among LDH isoenzymes were increased,the proportion of LDH3 was close to the baseline value,and the proportions of LDH4 and LDH5 were 0 when stored at -20 ℃ for 30 d. Conclusions At 2-8 ℃,0.5-1.25 mol/L betaine stabilizes total serum LDH activity for at least 30 d. Serum LDH is unstable when stored at -20 ℃.

Key words: Lactate dehydrogenase, Isoenzyme, Betaine, Storage temperature