Usefulness of biological variation in the establishment of delta check limits

doi:10.1016/j.cca.2016.08.007

Clinica Chimica Acta

Volume 463, 1 December 2016, Pages 18-21

https://doi.org/10.1016/j.cca.2016.08.007 Get rights and content

Highlights

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A large difference was observed between the nine routine chemistry tests in the percentage exceeding the delta check limits by RCV.
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Delta percent changes of the paired test results of protein, albumin, Na, K and Cl showed a symmetric distribution
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Delta percent changes of the paired test results of glucose, AST, ALT and creatinine showed an asymmetric distribution
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A good correlation was found between CV_I and the delta check limits according to population distribution and a closer correlation was observed when using the test items with CVi of < 5.0%.

Abstract

Background

Biological variation is used in the calculation of reference change values (RCVs) for a delta check. In this study, we examined the correlation between intra-individual biological coefficients of variation (CV_I) and delta check limits according to population distribution.

Methods

A total of 1,533,359 paired test results of nine routine chemistry tests were used to make the population distributions of delta percent changes. Their 0.5th, 2.5th, 97.5th, and 99.5th percentiles were then used for delta check limits.

Results

A large difference was observed between the chemistry tests in the percentage exceeding the delta check limits according to the RCVs. The mean percentage of test results of each test item exceeding the delta check limits of RCV_95% ranged from 12.3% to 40.6%. Delta percent changes of protein, albumin, sodium (Na), potassium (K) and chloride (Cl) showed a symmetric distribution. However, an asymmetric distribution was observed in the delta percent changes of glucose, aspartate transaminase (AST), alanine aminotransferase (ALT) and creatinine. A good correlation was observed between CV_I and the delta check limits according to population distribution and a closer correlation was observed when using the test items with CV_I of < 5.0%.

Conclusions

Intra-individual biological coefficients of variation (CV_I) would be useful for the establishment of delta check limits.

Introduction

Rapid reporting of accurate test results is the main goal of clinical laboratories. In many clinical laboratories, test results are auto verified in order to reduce errors and to report the results more rapidly [1]. Autoverification is a method of examining test results using several tools including quality control results, instrument flagging, moving averages, critical limits, and delta checks [2].

A delta check compares a patient's current and previous results using difference percentage, absolute difference or ratio [3], [4]. A large difference between two consecutive test results is likely indicative of test errors and the patient needs to be retested to rule out errors. Although the delta check is a powerful tool for detecting errors in clinical laboratories, adequate delta check limits are needed. If the delta check limit is set too low compared with biological variation and analytical variation, many test results will exceed the delta check limit. Conversely, if the delta check limit is set too high, many false negatives will result. Therefore, it is crucial to set adequate delta check limits.

Delta check limits have been established using pathologists' experience, reference change values (RCVs) or population distribution of two consecutive test results [5], [6]. An RCV is determined from intra-individual biological variation and analytical variation, and has been considered to be an objective guide for interpreting numerical test results in clinical laboratory serial testing [7], [8]. However, few studies on delta check limits using RCV have been reported. In this study, we examined the difference between the delta check limits by RCV and by the population distribution. We then evaluated the correlation between the intra-individual biological coefficients of variation (CV_I) and the delta check limits from the population distribution.

Section snippets

Data collection

The test results for nine routine chemistry tests were collected from the The Catholic University of Korea, St. Vincent's Hospital between January and December 2014. The tests included glucose, aspartate transaminase (AST), alanine amimotransferase (ALT), creatinine, total protein, albumin, sodium (Na), potassium (K), and chloride (Cl). A total of 1,893,955 tests were performed. One year was used for the time interval for the delta checks. These tests were performed using a model 7600–110

Results

A total of 1,893,955 test results were obtained (Table 1). Of all the patients with test results, about 81% (1,533,359) had been previously tested within 1 y. For chloride total test results, 76.3% of patients and for creatinine total test results, 82.8% of patients had previous test results.

The smallest delta check limit of RCV_95% was sodium (± 3.1%) and the largest delta check limit was ALT (± 67.6%) (Table 2). Delta check limits of RCV_99.9% of the routine chemistry tests were about twice those

Discussion

Our study shows that many test results exceeded the delta check limits by RCV_95%, RCV_99%, and RCV_99.9%. The mean percentage of test results of each item exceeding the delta check limits of RCV_95% ranged from 12.3% to 40.6%, which was greater than the expected percentage. In addition, a large difference was observed between the nine routine chemistry tests in the percentage of test results exceeding the delta check limits according to RCV. These findings suggest that the RCV has limitations for

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View full text

Usefulness of biological variation in the establishment of delta check limits

Highlights

Abstract

Background

Methods

Results

Conclusions

Introduction

Section snippets

Data collection

Results

Discussion

Current status of verification practices in clinical biochemistry in Spain

Clin. Chem. Lab. Med.

Autoverification of Clinical Laboratory Test Results; Approved Guideline

An evaluation of the detection capacity of a computer-assisted real-time delta check system

Clin. Chem.

Rate and delta checks compared for selected chemistry tests

Clin. Chem.

New decision criteria for selecting delta check methods based on the ratio of the delta difference to the width of the reference range can be generally applicable for each clinical chemistry test item

Ann Lab Med

Reference change values

Clin. Chem. Lab. Med.