Mechanism: As a solution freezes there is an uneven distribution of solute and solvent, with more solute in the center and more solvent at the periphery. The periphery thaws first, so a partially thawed specimen has a relative excess of solvent, causing the specimen to be dilute until thawing is complete and the specimen has been remixed.
Any specimen can be affected, but it would usually be a serum specimen since the tubes are more likely to freeze. On the other hand, a frozen urine specimen might be more likely to be partially thawed.
Features:
(1) Several laboratory values on a specimen are lower than expected.
(2) A fresh, redrawn specimen shows higher values for these analytes.
(3) The original specimen may have been frozen intentionally or by accident.
(4) The original specimen had been thawed just prior to the original testing.
(5) Retesting the original specimen after careful thawing and mixing shows higher values for the previously low analytes. These may be same but are often higher than for the redrawn specimen.
If specimens were accidentally frozen in transport, then whole blood samples in the shipping container should be hemolyzed. The serum will be reddish and the potassium will be elevated. If all of the samples were serum, then freezing during transport may go undetected.
Freezing during transport can occur:
(1) during the winter if not properly packaged
(2) placing the tube in direct contact with an ice pack
(3) shipping in an unpressurized airplane flying at a high altitude
(4) putting the specimen in a malfunctioning refrigerator
(5) putting the specimen in a freezer instead of a refrigerator
Differential diagnosis:
(1) deterioration of analyte during freeze/thaw cycle
(2) specimen mix-up
(3) analytical instrument failure
