Effect of long-term freezer storage, thawing, and refreezing on selected constituents of serum

We determined the effect of long-term freezer storage and repeated thawing and freezing of serum on concentrations of electrolytes (sodium, potassium, calcium, and phosphate), enzymes (aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, and creatine kinase), total protein, tumor markers (carcinoembryonic antigen and alpha-fetoprotein), and other substances. Vials (1 ml) of frozen serum from a single blood drawing from 40 women with no breast disease and 70 with benign breast disease were analyzed annually from 1983 to 1987. Blood had been obtained from 40 subjects in 1978, 40 in 1980, and 30 in 1983. Thawing and refreezing studies were done in two ways: (1) serum samples from 30 subjects with benign breast disease were thawed at weekly intervals for 6 weeks and (2) serum samples from 30 patients with stage IV breast cancer were analyzed for alpha-fetoprotein and carcinoembryonic antigen, and serum specimens from 23 patients with benign breast disease and 7 control subjects were analyzed for lactate dehydrogenase and creatine kinase after thawing and keeping the samples at room temperature for up to 4 hours and then refreezing them. For measuring laboratory variability, duplicate samples were processed. Long-term storage (up to 10 years) and repeated thawing and refreezing did not affect the results of any tested constituents of serum. Although most measurements showed statistically significant variability over test cycles, these differences were thought to be due to laboratory variability.