Effects of Sample Freezing on Ion-Selective Electrode Determinations of Serum Calcium

Abstract

We assessed in a prospective study the effects of freezing, thawing, and prolonged storage of serum samples for ionized calcium determinations with the "Clin ± Ion." Forty-eight serum samples were collected before and during infusions of EDTA and calcium into human subjects. Values for ionized calcium in serum samples stored frozen for one and six months were similar to those determined for fresh specimens. Samples stored for 12 months had significantly (p <0.001) lower values. Thawing and refreezing the sample within the first six months did not alter values. We conclude that serum samples can be frozen and stored for as long as six months without affecting results for ionized calcium determinations.