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Clinical Chemistry 50: 1273-1275, 2004; 10.1373/clinchem.2004.034421
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(Clinical Chemistry. 2004;50:1273-1275.)
© 2004 American Association for Clinical Chemistry, Inc.

Letters to the Editor

Interference in the Vitros CREA Method When Measuring Urine Creatinine on Samples Acidified with Acetic Acid

Linda Lambert, John Caban and Dennis W. Jaya

1 Department of Pathology, St. Jude Children’s, Research Hospital, Memphis, TN

aAddress correspondence to this author at: Department of Pathology, Mailstop 250, St. Jude Children’s Research Hospital, 332 N. Lauderdale St., Memphis, TN 38105-2729. Fax 901-495-3100; e-mail dennis.jay@stjude.org.

The first 20% of the full text of this article appears below.


To the Editor:

The addition of additives to stabilize one analyte in a sample can adversely affect the measurement of other analytes. Urine samples for homovanillic acid (HVA) and vanillylmandelic acid (VMA) analysis are acidified to pH 2–4 to maintain analyte stability. This is typically done with either glacial acetic acid or HCl. In a pediatric population, we analyze random urine samples rather than 24-h collections, and report the ratio of either HVA or VMA concentration to creatinine concentration. We investigated the effects of acetic acid and HCl on the creatinine assay performed on the Vitros 950 analyzer (Ortho-Clinical Diagnostics). The Vitros CREA instructions state that for urine "The following preservatives have been tested and demonstrated an effect of <2% on creatinine results ... " with glacial acetic acid and 12 mol/L HCl included in the list (1). We have verified that HCl causes negligible interference but have found significant positive interference with the use of acetic acid.

For 20 urine samples, two 5-mL aliquots were apportioned and acidified to pH 3. pH was measured with colorpHast pH strips, pH range 0–6 (EMD Chemicals). One portion was acidified with 6 mol/L HCl (Fisher Scientific) and the other with 50% glacial acetic acid (Fisher Scientific). We then measured creatinine in the untreated urine and each of the acidified aliquots, using a 1:21 dilution according to . . . [Full Text of this Article]

Neil Greenberga, Thomas A. Smith and Nicholas VanBrunt

R1 Ortho-Clinical Diagnostics, Inc., Rochester, NY

aAddress correspondence to this author at: Ortho-Clinical Diagnostics, Inc., 100 Indigo Creek Dr., Rochester, NY 14626-5101. Fax 585-453-3368; e-mail ngreenbe@ocdus.jnj.com.






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