Some Issues Concerning the Normalization of Laboratory Data Based on Reference Ranges
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Drug Information Journal, Vol. 35, pp. 153-156. 2001 Printed in the USA. All rights reserved.
SOME ISSUES CONCERNING THE NORMALIZATION OF LABORATORY DATA BASED ON REFERENCE RANGES CHRISTY CHUANG-STEIN Clinical Biostatistics I, Pharmacia Corporation, Kalamazoo, Michigan
In this paper, we examine three issues associated with normalizing lab data based on reference ranges: normalized values being negative, lab values being excluded because of missing information on reference ranges, and normalized leukocyte differentials not adding up to 100%. We propose solutions to tackle these issues. Even though we propose solutions, we continue to emphasize the importance of using central laboratories as much as possible and regard normalization only as the last resort. Key Words: Assay detection limit; Estimation; Leukocyte differentials; Normalization; Reference range
INTRODUCTION LAB DATA ARE routinely collected and assayed in clinical trials to ensure that patients are not experiencing untoward toxicities. Kirby (1) and Pitts (2) discussed the role and usefulness of laboratory parameters in both clinical practice and drug trial settings. Even though central laboratories are increasingly used to process lab specimens in multicenter trials, there continue to be situations where multiple laboratories are used in a multicenter study. There are also situations when lab results need to be combined from different studies to detect signals for lab toxicities. In the latter case, even if a central laboratory was used in each trial, there is no guarantee that the same central laboratory was used in all the studies. As a result, pooling lab data from different laboratories continues to be a challenge faced by trial analysts.
Reprint address: Christy Chuang-Stein, Clinical Biostatistics I, Pharmacia Corporation, 7000 Portage Road, Kalamazoo, MI 49001.
Chuang-Stein (3) proposed a method to adjust lab values based on reference ranges. The procedure selects a set of reference ranges against which to normalize all values. To be specific, let X represent an assay value with a corresponding reference range of (Lx,Ux). Furthermore, let (Ls,Us) be the reference range chosen to be the standard range for the assay under discussion. Chuang-Stein proposed normalizing X relative to (Ls,Us) through the following expression:
In (l), Xs represents the normalized value of X. This normalized value satisfies:
In other words, X and Xs are of the same unit distance from Lx and Ls respectively, where a unit distance is defined by Ux - Lx and Us - Ls under the two sets of reference ranges.
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Chriszy Chuang-Stein
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In this paper. we will discuss three issues associated with the above normalization procedure. The first issue relates to normalized values that are negative. The second issue occurs in situations when one or both of the limits of a reference range are missing. The third issue concerns the normalized leukocyte differentials routinely reported for hematological evaluatio
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