The influence of different sample collection types on the levels of markers used for Down's syndrome screening as measured by the Kryptor Immunosassay system.

BACKGROUND

In a rapid point-of-care screening programme for chromosomal anomalies, analysis of biochemical markers in maternal blood can now be accomplished in a rapid time frame (less than 20 min). The need to leave whole blood samples some 10 min for coagulation and a further 5 min for centrifugation adds additional processing time.

METHODS

The possibilities for reducing this processing time were investigated using various anticoagulated blood collection systems and the Kryptor analytical platform. Plasma levels of alpha-fetoprotein (AFP), pregnancy-associated plasma protein-A (PAPP-A) and free human chronic gonadotrophin beta-subunit (beta-hCG) were compared with those in maternal serum.

RESULTS

From the mean results from ten patients it was shown that use of heparin plasma resulted in a statistically significant reduction in levels of PAPP-A and that EDTA plasma reduced the levels of PAPP-A dramatically. For AFP, levels in citrated plasma and EDTA plasma were also significantly reduced, whereas levels of free beta-hCG were not affected.

CONCLUSION

Use of alternative sample types for PAPP-A is not possible. The sample of choice for first trimester screening using the Kryptor platform is maternal serum.