While evaluating antibody responsiveness is usually the deciding factor in assessing the relevance of milder reductions in IgG levels in the clinically relevant scenario, why are there such variations in what different labs and various textbooks cite as normal levels of immunoglobulins? For example, Stiehm's text lower limit of normal for an adult is 548 mg/dl; local hospital lab's is 641 mg/dl. Should our reference texts' values be the standard or accept the lab's reported normals?


Thank you for your inquiry.

All laboratories are responsible for setting internal standards and reference ranges. Often analytes are sent out to laboratories across the country to see how well laboratory results correlate with one another. All of this is held to standards that are monitored by pathology societies. There is a text entitled “Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline, Third Edition” (see below). The paragraph below is copied from the website offering this edition and describes this text.

So, it is not unusual that an analyte might have varying internal standards from one lab to the next. What is important is that these are repeatable and consistent, and are within the range of standards of other laboratories across the country. In addition, as new techniques are developed, those ranges may differ. If you would like to know more about this process, I have also copied for you below three website links which will lead you to discussions of this issue, free of charge.

Because of this, you should use the reference range of the lab you choose to do your tests.

Thank you again for your inquiry and we hope this response is helpful to you.

Establishing Reference Intervals for Clinical Laboratory Test Results
Is There a Better Way?

Range change—the latest on reference intervals

10.1309/LMEHV3HP39QOFJPA (2009) LabMedicine, 40, 75-76.
Determining Laboratory Reference Intervals: CLSI Guideline Makes the Task Manageable

Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline, Third Edition, C28A3E
Clinical and Laboratory Standards Institute document C28-A3--Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline--Third Edition is written for users of diagnostic laboratory tests. It offers a protocol for determining reference intervals that meet the minimum requirements for reliability and usefulness. The guideline focuses on health-associated reference values as they relate to quantitative clinical laboratory tests. Included are various requirements for studies to determine reference values for a new analyte or a new analytical method of a previously measured analyte. Also discussed is the transfer of established reference values from one laboratory to another.

Phil Lieberman, M.D.

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