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Reference Range Change Limit

Maria Grana writes, Hello George, what would constitute a “significant change” when performing the yearly reference range study for coagulation? Thanks.

Hello, Maria, and thank you for your question. The laboratory director and staff often establish an acceptable reference range (reference interval, normal range) change limit, beyond which it is necessary to publish a new interval. The same applies to therapeutic ranges, for instance, the partial thromboplastin time (PTT) therapeutic range, in seconds, for unfractionated heparin therapy. I’ve heard that 10% is a reasonable limit, however that may vary depending upon the assay. I’m forwarding this question to a few of our participants for additional comments, as I’d like to know what limits our colleagues use. The Clinical and Laboratory Standards Institute (CLSI) document that addresses this isEP28-A3c, Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline—Third Edition.

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