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Clinical Chemistry 52: 161, 2006; 10.1373/clinchem.2005.061069
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(Clinical Chemistry. 2006;52:161.)
© 2006 American Association for Clinical Chemistry, Inc.

Letters to the Editor

First-Trimester Down Syndrome Screening: Reply

Glenn E. Palomaki1,a, George J. Knight1, Louis M. Neveux1, James E. Haddow1 and Raj Pandian2

1 Division of Medical Screening, Department of Pathology, and Laboratory Medicine, Women & Infants Hospital, Providence, RI
2 Quest Diagnostics, Nichols Institute, San Juan Capistrano, CA

aAddress correspondence to this author at: Division of Medical Screening, Department of Pathology and Laboratory Medicine, Women & Infants Hospital, Providence, RI 04039. Fax 207-657-7887; e-mail gpalomaki{at}ipmms.org.


To the Editor:

We welcome the opportunity to clarify the points made by Hallahan and his colleagues concerning our report of maternal serum invasive trophoblast antigen (ITA) measurements and Down syndrome screening in the first trimester (1). Findings from the one other independent report of serum ITA in the first trimester are consistent with ours (2). With any new marker, such as ITA, the process of evaluation begins with reports such as ours. Now that an assay system suitable for routine use is available (3), additional reports are likely to follow.

Our study used published, widely accepted population parameters and modeling techniques to derive expected detection and false-positive rates for the various combinations of first-trimester markers (4)(5). Using data from our earlier study (6) and our present study (1), we obtained similar univariate detection rates for the 3 markers at a false-positive rate of 5% [detection rates of 29% for human chorionic gonadotropin (hCG), 25% for free ß-subunit, and 28% for ITA]. Neither this nor any other published study will contain the 3500 observations in Down syndrome pregnancies necessary to have an 80% power to detect a 3% difference in detection rates. For this reason, the screening community relies on modeling when comparing various marker combinations.

The data presented in Tables 1–3 of our report are correct (1). The footnotes for the tables, however, were not updated when we analyzed the results using the SURUSS parameters (4)(5). The description of our modeling methodology and the use of the SURUSS parameters are accurate, with the exception that the correlation coefficients between serum markers and nuchal translucency (NT) measurements were set to zero. This is the most equitable way to compare the 3 markers in the absence of reliable estimates for the correlations between NT and ITA measurements in case and control pregnancies.

We conclude that ITA (or hCG) measurements could be an acceptable replacement for measurements of the free ß-subunit of hCG when NT measurements are included as part of first-trimester Down syndrome screening.


References

  1. Palomaki GE, Knight GJ, Neveux LM, Pandian R, Haddow JE. Maternal serum invasive trophoblast antigen and first-trimester Down syndrome screening. Clin Chem 2005;51:1499-1504.[Abstract/Free Full Text]
  2. Weinans MJ, Sancken U, Pandian R, van de Ouweland JM, de Bruijn HW, Holm JP, et al. Invasive trophoblast antigen (hyperglycosylated human chorionic gonadotropin) as a first-trimester serum marker for Down syndrome. Clin Chem 2005;51:1276-1277.[Free Full Text]
  3. Pandian R, Lu J, Ossolinska-Plewnia J. Fully automated chemiluminometric assay for hyperglycosylated human chorionic gonadotropin (invasive trophoblast antigen). Clin Chem 2003;48:808-810.
  4. Wald NJ, Rodeck C, Hackshaw AK, Walters J, Chitty L, Mackinson AM. First and second trimester antenatal screening for Down’s syndrome: the results of the serum, urine, and ultrasound screening study (SURUSS). J Med Screen 2003;10:56-104.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
  5. Wald NJ, Rodeck C, Hackshaw AK, Rudnicka A. SURUSS in perspective. Br J Obstet Gynaecol 2004;111:521-531.
  6. Haddow JE, Palomaki GE, Knight GJ, Williams J, Miller WA, Johnson A. Screening of maternal serum for fetal Down’s syndrome in the first trimester. N Engl J Med 1998;338:955-961.[Abstract/Free Full Text]




This Article
Right arrow Extract Freely available
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Right arrow Alert me when this article is cited
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Right arrow Articles by Palomaki, G. E.
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Related Collections
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