Assessment of six sigma metrics applications of quality control in clinical biochemistry laboratory

 

 

Abstract               Errors in clinical biochemistry laboratory are mainly due to the poorly designed quality control system. Six sigma is an error detection method which is first implemented by Motorola Company. Sigma stands for standard deviation. This is used whenever an outcome of process has to be measured. A poor outcome means an error or defect. The main objective of this study was to calculate six sigma for chemistry parameters run on Cobas 6000, Roche Diagnostics. After consulting statistician, 14 months Internal Quality Control values and External Quality Assurance System values were extracted for clinical chemistry parameters. Using coefficient of variation, percentage of bias, total allowable error, six sigma were calculated for each parameters. This study showed that following parameters had six sigma above6: total protein, alanine transaminase, aspartate transaminase, alkaline phosphatase, total bilirubin, creatinine, high density cholesterol and triglycerides, six sigma 3-6: albumin, direct bilirubin, urea and total cholesterol and none had sigma values less than 3. To conclude six sigma values for clinical biochemistry laboratory indicates that the maintenance quality of the lab.

Key Word: Coefficient of variation, Clinical biochemistry, Quality, Six sigma

 

INTRODUCTION

Six sigma metrics is mathematical symbol used for the standard deviation and applied successfully by Motorola. This method can be applied wherever an outcome of a process has to be measured. It guides about the degree to which any process deviates from its goal. Sigma metrics defines how many sigma fits within the tolerance limits.¹ If the six sigma value is more than 3 then laboratory performance is satisfactory,^3-6 then laboratory performance is good and if it is more than 6 then laboratory performance is excellent. Hence it is accepted as ‘world class quality². Coefficient of variation helps to understand the comparison of the overall precision of the laboratory instruments. If standard deviation alone used for comparing precision for two different methods then it can be easily misled³. In health care services, particularly clinical laboratories have utmost importance because physicians make their clinical decisions mostly in accordance with laboratory results, thus reporting of accurate results are crucial, this in turn makes laboratory personnel to evaluate the laboratory performance using sigma metrics and implement the necessary quality control system.^4,5  Quality management in clinical biochemistry laboratories includes quality standards which are internal quality controls (IQC) and external quality assurance scheme (EQAS). Internal quality control is run daily by the laboratories and it is interpreted using standard Westgard rules. External quality assurance scheme is a program in which multiple specimens are periodically sent to members of a group of laboratories for analysis and/or identification; in which each laboratory’s results are compared with those of the other laboratories in the group and/or with an assigned value, and reported to the participating laboratory and others. Poor outcomes counted as an error or defects. It is possible to assess the quality assurance and management of the laboratory testing process and the quality control that is needed to ensure that the desired quality is achieved.^6,7 The aim of the study is to evaluate the performance and quality of chemistry parameters of clinical biochemistry laboratory by calculating the sigma metrics for individual parameters.

 

MATERIALS AND METHODS

14 months internal and external quality control data were taken for the chemistry parameters like urea, creatinine, Aspartate transaminase (AST), Alanine transaminase (ALT), Alkaline phosphatase (ALP), Total Bilirubin, Direct Bilirubin, Albumin, Total protein, Total cholesterol (TC), High Density Lipoprotein (HDL), Triglycerides (TG).

• A coefficient of variance (CV) was calculated from internal quality control for these parameters.
• Percentage Bias for these parameters was from External quality assurance scheme. The external quality control is provided by BIO-RAD and it is run once in a month and it is interpreted by Z score and standard deviation index.
• The total allowable error (TEA) was followed as per clinical laboratory improvement amendment (CLIA) Guidelines.
• BIAS was calculated from BIAS=(Mean of all laboratories using same instrument and method-Our mean)/(Mean of all laboratories using same instrument and method)X100
• Sigma metrics was calculated from CV, Percentage Bias and total allowable error using this formula for every month using internal quality control and external quality control data of the above mentioned parameters.

 Sigma Metrics= (%TEA-%BIAS)/%CV Data were compiled and statistical methods like mean, standard deviation and correlation were used, p value <0.05 was said to be significant.

Ethical approval: This article does not contain any studies with human participants or animals performed by any of the authors.

 OBSERVATION AND RESULTS

 

Table1: Showing mean coefficient of variation of chemistry parameters for 14 months

 

Table 2: Showing sigma values of chemistry parameters for month 1- 7

Table 3: Showing sigma values of chemistry parameters for month 8-14

 

Table 4: showing sigma values of serum lipid profile, urea and creatinine for month 1-7

 

Table 5: showing sigma values of serum lipid profile, urea and creatinine for month 8-14

 

DISCUSSION

Every laboratory must design their own quality control procedure to assure that patient results are reported in accordance with the quality standards. A good laboratory practice is to have well developed quality control systems. Using the statistical concept six sigma laboratory errors can be reduced by maintaining the sigma value at 6 ^{8, 9}. Thus this analysis assesses the efficiency of existing laboratory processes and helps in the better maintenance of quality control systems in the lab. The results of clinical biochemistry laboratory showed that parameters such as total protein, ALT, AST, and ALP, total bilirubin, creatinine, HDL-cholesterol and triglycerides had sigma value above 6 which means the laboratory performance is excellent. Higher the sigma value means lower the defects/errors. High sigma value offers a high level of quality at reduced cost. It can also boast of time efficient, effective work flow with higher degree of patient/ doctors satisfaction⁸. Similarly albumin, direct bilirubin, urea and total cholesterol parameters showed sigma value 3-6 which means their performance is good. Thus excellent performance was noted for most of the chemistry parameters of clinical biochemistry laboratory of Kasturba Hospital, Manipal. Sigma metrics provide scope for continuous improvement. Looking at the IQC results, EQAS results and six sigma metrics can establish or redefine quality control strategy design.  Many studies conducted at different part of India also felt the same.

CONCLUSION

Good sigma values can be seen in most of the parameters indicates the good laboratory practice in quality control and management. Assessment of Six sigma is easy and reliable method to adopt as a part of quality control in all the clinical laboratories. Six sigma which does not require more efforts values keeps the laboratory to maintain the quality and standard of patient reports.

Limitations of the study:

Some of the parameters did not have complete 14 months data. Analysis of lab performance should be done at the regular interval of time.

 

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