Correspondence

Normal Reference Laboratory Values?

N Engl J Med 1993; 328:141-142January 14, 1993

Article

To the Editor:

Jordan et al. (Sept. 3 issue)1 provided a list of normal reference laboratory values that was prefaced by the statement “Reprints are available at $2.50 each,” implying that these values are reference values for clinical laboratories. After the publication of the article, several physicians called us to question our normal values and cited the article as a reference. For each analyte, the authors listed only the method used, without specifying the particular instrument or reagent. A brief description of the procedure the authors used to establish these values would have helped other laboratories to generate their own normal values2. Normal reference values obtained with use of the same method may differ, depending on the instrument and reagent used. For each analyte, the authors should have listed the method, instrument, and reagent used2,3. In addition, listing the neutrophil reference values as a percentage of the white-cell count rather than an absolute number is misleading. The Journal should assume a leadership role in combating this common yet deficient practice.

The authors should have stated in a disclaimer that normal reference laboratory values may differ from one population to another2. Finally, a change in the title to “Normal Reference Laboratory Values Used by Massachusetts General Hospital for the Weekly Clinicopathological Exercises” might better reflect the intent of the article.

Habib A. Sioufi, M.D.
Boston Specialty and Rehabilitation Hospital, Mattapan, MA 02126

May S. Jacobson, Ph.D.
Children's Hospital, Boston, MA 02115

3 References

1. 1

   Jordan CD, Flood JG, Laposata M, Lewandrowski KB. Normal reference laboratory values. N Engl J Med 1992;327:718-724
   Full Text | Web of Science | Medline

2. 2

   Galen RS. The normal range: a concept in transition. Arch Pathol Lab Med 1977;101:561-565
   Web of Science | Medline

3. 3

   Lott JA, Tholen DW, Massion CG. Proficiency testing of enzymes: charting the way toward standardization. Arch Pathol Lab Med 1988;112:392-398
   Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: The process of developing a table of reference values requires many decisions about the information to be included, and the information selected must be compatible with the space limitations of the Journal. It was not our intent to provide a lengthy, exhaustive compilation of reference-value data, since this information is widely available in standard textbooks. As stated in the introduction, our purpose was to provide general information on commonly performed tests for use with the Case Records Weekly Clinicopathological Exercises. We avoided providing additional detailed information on methods, reagents, and instruments for two reasons. First, we frequently find it necessary to modify or change methods or reagents, which often does not significantly affect the reference ranges. Therefore, to provide anything more than the general methods used would quickly render the reference table out of date as new methods are introduced in the clinical laboratories of Massachusetts General Hospital (MGH). Second, most of the tests performed at MGH involve the use of commercial kits or reagents. Referring to instruments, methods, and reagents in more than general terms could be interpreted as an endorsement by our hospital or the Journal, a suggestion we wish to avoid.

The procedure used to estimate reference values varies with the test. In some cases, the estimation of the reference range is straightforward; in others, it involves many variables. We chose not to provide details on the estimation of the reference ranges; the subject is treated at length in most textbooks of laboratory medicine. For this reason, the introductory paragraph includes a statement that the ranges reported reflect only the reference values used at MGH. Estimates of reference ranges are affected by many variables, such as the test methods and the age and sex of the population studied. In some cases the ranges used at MGH will not be appropriate for a test performed at another institution. Whenever feasible, each institution should determine its own reference values.

Finally, the listing of the neutrophil reference values as a percentage of the whole blood count (as opposed to the absolute number) does not represent a value judgment about the optimal method of reporting this result. Rather, it reflects the current practice in our institution to consider both the percentage of the white-cell population represented by neutrophils and the absolute neutrophil count. By analogy, the bleeding-time test is considered to be without value by many, but because it is still used by some practitioners, it was included in the table.

Kent B. Lewandrowski, M.D.
James G. Flood, Ph.D.
Michael Laposata, M.D., Ph.D.
Massachusetts General Hospital, Boston, MA 02114