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Down's syndrome screening using free beta hCG: instability can significantly increase the Down's risk estimate
J M Beaman1, N Akhtar, D J Goldie
1Department of Clinical Chemistry, Lewis Laboratories, Southmead Hospital, Bristol, UK.
Annals of Clinical Biochemistry
|November 1, 1996
Summary
Delayed separation of blood samples significantly increases free beta hCG levels, impacting Down
Area of Science:
- Biochemistry
- Clinical Chemistry
- Reproductive Biology
Background:
- Free beta hCG (human chorionic gonadotrophin) is a key biomarker in prenatal screening.
- Accurate measurement of free beta hCG is crucial for reliable Down's syndrome risk assessment.
- Sample handling and stability can potentially affect biomarker concentrations.
Purpose of the Study:
- To evaluate the stability of free beta hCG in unprocessed blood samples.
- To determine the impact of delayed sample separation on free beta hCG levels.
- To assess the effect of these changes on Down's syndrome risk stratification.
Main Methods:
- Assessed free beta hCG stability using a dual alpha-fetoprotein and free beta hCG assay.
- Analyzed heparinized and clotted blood samples after varying periods of unseparated storage (24h to 96h).
- Calculated the change in Down's syndrome risk estimates based on altered free beta hCG concentrations.
Main Results:
- A significant increase in free beta hCG concentration was observed in samples unseparated for 24 hours or more.
- Mean free beta hCG increase was 10.2% after 24h and 45.7% after 96h (P < 0.001).
- Delayed separation led to increased Down's risk estimates, altering risk classification in some cases.
Conclusions:
- Delayed sample separation significantly affects free beta hCG stability.
- This instability can compromise the accuracy of Down's syndrome screening programs.
- Recommendations for timely sample processing are crucial for accurate prenatal risk assessment.