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Increasing hCG concentrations during storage at (+)4 degrees C with the Bayer Centaur Total hCG method
1Department of Clinical Chemistry, Royal Hallamshire Hospital, Sheffield, S10 2JF, UK. kevin.page@sth.nhs.uk
Background:
The interpretation of changes in serum human chorionic gonadotropin (hCG) concentrations in early pregnancy requires a knowledge of the day-to-day imprecision of the method at the concentrations measured. We therefore attempted to determine the analytical imprecision of our total hCG method over a 4-week period at concentrations up to 20,000 IU/L.
Methods:
Serum specimens with hCG concentrations between 100 and 20,000 IU/L were collected during early pregnancy and analysed using the Bayer Centaur Total hCG method at weekly intervals after storage at (+)4 degrees C and (-)20 degrees C.
Results:
The reproducibility of hCG results over a 4-week period in refrigerated specimens with an initial hCG concentration below 1000 IU/L was poor (mean coefficient of variation = 17.4%) and there was an apparent increase in serum hCG concentrations of up to 68%. Similar changes occurred in some specimens stored at (-)20 degrees C. Further experiments confirmed that significant increases can occur during the first week following specimen collection.
Conclusions:
Total hCG concentrations in serum specimens collected during early pregnancy increase significantly during storage when measured by the Bayer Centaur Total hCG method, possibly due to a conformational change in hyperglycosylated hCG. When this method is used for monitoring early pregnancy, specimens should ideally be analysed on the day of collection.
