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Dilution terminology.

Q In the hospital where I work, we are having a "dilution debate," because while documenting a sample before it is verified, most of us enter it as a x2 or x10 dilution--though some people prefer the 1:2 or 1:10 format. Confusion occurs when someone uses "1:1" as a dilution because if 1:10 means one part diluted with nine parts, making a total of 10 parts, then what does 1:1 mean? One part out of a total of one part, meaning "neat," or, as some people loudly state, "one part plus one part," meaning a x2 dilution? What proper terminology should we be using?

A Sharon Miller, a member of the MLO editorial advisory board, assisted me in answering this question. Clinical laboratory sciences students at Northern Illinois University receive the following information as part of their initial lab guidelines:

Terminology of dilutions is very important. Unfortunately, there is inconsistency in how dilutions are described. When water is added to relatively concentrated solutions or mixtures, they are being diluted. We say, for example, that we make a "1 in 10" dilution. This means that one volume of concentrate is mixed with nine volumes of water. A "1 in 100" dilution is one volume of concentrate in 99 volumes of water.

Avoid the expression "one-to-one dilution" or "one-to-two dilution." Those expressions are actually proportions, not dilutions. We can express dilutions as follows: a "1 in 10" dilution = 1:10; and "1 in 100" dilution = 1:100. A 1:2 or "1 in 2" dilution is prepared by taking 200 mL of concentrate and adding 200 mL of water to create 40 mL of solution.

--Daniel M. Baer, MD

Professor Emeritus

Department of Pathology

Oregon Health and Science University

Portland, OR
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Title Annotation:Answering your questions
Author:Baer, Daniel M.
Publication:Medical Laboratory Observer
Article Type:Brief article
Geographic Code:1USA
Date:Nov 1, 2007
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