Pcl Dec 51

σ

SIGMA METRIC

.พ. พญาไท

การเพิ่มประสิทธิภาพการทำาIQC หน่วยเคมีคลินิก

ดิมใช้ control rule 12s พบว่า Pfr (false rejection) สูง และมี Ped ( error detection)สูง แก้ไข

หา control rule ที่เหมาะสม

EZ rule

โดย กำาหนดค่าPfr<0.05%,Ped> 90% หาค่า sigma metric

สรุป เพื่อนำาสู่การ ปฏิบต ั ิ

Performance

Control rule

High

1 3.5s

For 5.0 Sigma values and above: 13s with N=2

13s /22s /R4s /41s /8x

For 4.0 to 5.0 Sigma values: 12.5s with N=2

sigma.>6 Moderate Sigma3.1-5.9

1 2.5s , 1 3s ,

Control Rule

1 3.5s

Low Sigma <3

13s /22s /R4s /41s /8x

For Sigma values below 4.0: "Westgard Rules" with N=2 SIX SIGMA CHEMISTRY: SOME REAL WORLD NUMBERS

SIX SIGMA CHEMISTRY: SOME REAL WORLD NUMBERS

ะมงกุฎ

า sigma metric เพื่อประเมินและพัฒนาคุณภาพทางห้องปฏิบต ั ิการโลหิตวิทยา

control rule 12s

พบว่า Pfr (false rejection) สูง และมี Ped ( error detection)สูง

ฒนา

alized OPSpec chart

วณหา Sigma metric ( data

เลือก QC rule , Pfr , Ped จาก process performance)

igma metric ที่มีการเปลี่ยนแปลง มิ.ย.- ก.ค. - ส.ค. - ก.ย. - ต.ค.

12s

13s

Control rule

Sigma metric

QC procedure

Process performance

False rejection Error detection

Inaccuracy Imprecision = (TEa-Bias)CV

Sigma

= (TEa-Bias)/CV

The long-term goal of six sigma quality management is to achieve an error rate of 3.4 or less per million opportunities For all laboratory processes. In percent terms, that’s an error rate of less than 0.001%.

>6 Sigma

It must be kept in mind that six sigma quality management is not only a tool for defining process performance but also a method for moving a process from its present error rate to a very low error rate

Sigma

= (TEa-Bias)/CV

Accuracy goal

=

1.5TEa/6

Precision goal

=

TEa/6

Quality goal index QG

=

( Bias /Accuracy goal ) ( CV / Precision goal )

Quality goal index (QGI) =

Bias / 1.5 CV

QGI <0.8

Problem Imprecision

0.8 - 1.2

Imprecision & Inaccuracy

>1.2

Inaccuracy

One cause of difficulty in reducing inaccuracy of automated tests is the variable error introduced when switching from one lot of calibrator to another. Achieving and maintaining six sigma quality performance requires a rigorous approach to calibrator lot changes

Advantages •Easy to calculate the sigma-metric; •Easy to teach to laboratory scientists; •Provides “rules of thumb” that are easy to apply: •If sigma-metric 6 or greater, any QC will do; •If sigma-metric 5 or greater, N=2 okay; •If sigma-metric 4, need N=4; •If sigma-metric <4, need multirule QC •If sigma-metric <3, need new method!

Disadvantages •Works only with analytical quality requirement of form TEa; •Provides a limited choices of rules and Ns; •Must document application manually and separately

Cost-effective QC is now practical With careful selection of control rules and the number of control measurements, the cost-effectiveness of laboratory testing processes can be optimized by: •Reducing false rejections and preventing wasteful repeat analyses; •Reducing the number of control measurements to the minimum necessary to assure the desired quality is achieving; •Maximizing error detection when necessary by use of multirule control procedures and the appropriate number of control measurements; •Simplifying QC procedures when possible by use of single rule control procedures having low false rejection rates.