CV% for ESR.CV% for ESR ESR - Eric S. Raymond
Q We are interested what is stated % CV for within-run imprecision im·pre·cise
impre·cisely adv. for determination of erythrocyte sedimentation rate Erythrocyte Sedimentation Rate Definition
The erythrocyte sedimentation rate (ESR), or sedimentation rate (sed rate), is a measure of the settling of red blood cells in a tube of blood during one hour. (ESR). Is there any published data? If there is not such, what value should we use for evaluation of a new analyzer analyzer /ana·ly·zer/ (an´ah-li?zer)
1. a Nicol prism attached to a polarizing apparatus which extinguishes the ray of light polarized by the polarizer.
2. ? What CV values should I expect when running sed-rate daily controls?
A Sedimentation-rate QC can be run using commercially available control materials. Typically, this material has two levels: one in the low normal range, and one in the elevated range. The CV is influenced not only by environment and technique but also by the testing method used. CV is defined as the ratio of the standard deviation In statistics, the average amount a number varies from the average number in a series of numbers.
(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers. (s) to the mean ([micro]) and is often reported as a percentage, or CV = s/m. Therefore, the CV obtained when running sed-rate control is inversely proportional See
See also: Inversely to the mean value for each level of control. Generally, the "normal" sed-rate control (level 1) produces a much higher CV than the "abnormal" sed-rate control (level 2), because the mean value of level 1 control is much lower than the mean value of level 2.
I was assisted in answering this question by Streck Inc., a manufacturer of a sedimentation-rate quality-control products. The company collects quality-control data from users of its product in a program called STATS.
Individual customer data from Streck's ESR control peer-group STATS database shows the range of mean, standard deviation, and CV values observed for three representative ESR methods as follows:
So far, we have discussed daily QC variability. The question asks, however, about within-run variation. Because some of the variables affecting day-to-day testing are less well-controlled, within-run variability is usually less than day-to-day variability.
Streck informed us, "To our knowledge, there are no published acceptance criteria for reproducibility reproducibility Lab medicine The degree of agreement among repeated measurements of a particular parameter, presented in terms of a standard deviation or coefficient of variation of the results in a set of measurements in ESR testing. When qualifying a new ESR method for inclusion on the control assay, we conduct a reproducibility study using multiple lots of control material to compare the variability of the new method to the variability of a similar established ESR method. We have observed CV%'s for L2 (abnormal) control in the range of 2% to 10%. CVs for L1 (normal) control are substantially higher due to the smaller mean value of the L1 material. CV%s for fresh patient samples will vary according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. the magnitude of the patient's ESR result. A patient specimen with an elevated sed-rate will produce a lower CV% than a normal patient specimen in a reproducibility study, just as L2 control has a lower CV% than L1 control."
ESR Method Level Mean SD CV Streck ESR-Auto Plus 1 6 to 8 1 to 2 14% to 28% Diesse Mini-Ve 1 6 to 8 1 to 2 15% to 39% Polymedco Sediplast 1 2 to 7 1 to 2 18% to 34% Streck ESR-Auto Plus 2 79 to 93 2 to 6 3% to 7% Diesse Mini-Ves 2 81 to 95 2 to 6 3% to 7% Polymedco Sediplast 2 38 to 52 5 to 7 11% to 15%
--Daniel M. Baer, MD
Professor Emeritus e·mer·i·tus
Retired but retaining an honorary title corresponding to that held immediately before retirement: a professor emeritus.
Department of Pathology pathology, study of the cause of disease and the modifications in cellular function and changes in cellular structure produced in any cell, organ, or part of the body by disease.
Oregon Health and Science University
MLO's "Tips from the Clinical Experts" provides practical, up-to-date soluations to readers' technical and issues from a panel of experts in various fields. Readers may send questions to Dan Baer by e-mail at email@example.com.
Daniel M. Baer, MD, is professor emeritus of laboratory medicine at Oregon Health and Science University in Portland, OR, and a member of MLO's editorial advisory board.
Edited by Daniel M. Baer, MD