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To the Editor: In reading the study by Dr Dhallan and colleagues¹ regarding the percentage of fetal DNA recovered from the maternal circulation following formaldehyde treatment, we were concerned that a serial dilution method was used for estimating the fractional concentrations of fetal DNA in maternal plasma, since previous publications in this field have used real-time quantitative polymerase chain reaction (PCR) for this purpose.^2-3 One would expect the serial dilution method to be less accurate and less precise than the real-time PCR method. For a given sample that is serially diluted, a test aliquot from the most diluted tube at the end of the series may be positive in one experiment and negative in another, with a frequency described by the Poisson distribution. This would result in a wider confidence interval for the measured fractional concentration of fetal DNA in maternal plasma than would real-time PCR, decreasing the precision . . . [Full Text of this Article]

Y. M. Dennis Lo, DM
loym@cuhk.edu.hk

Rossa W. K. Chiu, FRCPA; K. C. Allen Chan, MRCP; Grace T. Y. Chung, PhD
Department of Chemical Pathology
Chinese University of Hong Kong
Prince of Wales Hospital
Shatin, New Territories
Hong Kong Special Administrative Region, China

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