1. Fibrinogen Low Abnormal
1 Grupo Bioquímico, Laboratorio Central del Hospital Italiano de Buenos Aires. 2 Universidad Favaloro. Buenos Aires, Argentina
Six SIGMA metric seems not to be applicable as a good quality tool for most laboratory tests of haemostasis
Barrera LH, Martinuzzo ME, Cheluja MG, D’Adamo MA, Otaso JC, Giménez MI, Oyhamburu J.
Grupo Bioquímico Laboratorio Central - Hospital Italiano de Buenos Aires. Tte. Gral. J.D. Perón 4190 – Tel/Fax:
Background
RESULTS
The concept of Six Sigma is that the performance goal of any production process is 6-sigma, which means that 6 sigmas or standard deviations of process variation should fit within the tolerance limits of the process or the quality requirement. Through this measurement it is possibly to obtain the number of defects per million (DPM) opportunities, being the goal to achieve less than 1 DPM, that correspond to 6 sigmas of process variation fit within the quality requirement.
Six Sigma Metric analyses have been greatly expanded as a tool for clinical laboratories, to measure their procedures performance as a whole. For the calculation of SIGMA the BIAS %, CV%, and allowed Total Error (TEA) of the test are used. In Haemostasis different TEA, according to different requirements are used: CLIA, CAP and biological variation (BV)
TP normal
TP Abnormal
BIAS
3,74%
CV%
Sigma BV
SIGMA CLIA
SIGMA CAP
TEA
5,3 15 20
Median
4,425
0,41
2,61
3,73
4,46
3,74
Min-Max
4,06-6,41
0,28-0,56
1,80-3,53
2,58-5,07
3,28-5,52
0,29-0,53
1,83-3,50
2,62-5,02
SIGMA 3-6
(%)
16,7
91,7 25 75
APTT normal
APTT Abnormal
BIAS
3,2%
CV%
Sigma BV
SIGMA
CLIA /CAP
SIGMA CLIA/CAP
TEA
4,5 15
Median
1,45
0,90
8,14
2,42
0,54
4,88
Min-Max
1,01-2,53
0,51-1,29
4,66-11,7
1,74-3,31
0,39-0,75
3,56-6,78
SIGMA 3-6
(%)
100
Fibrinogen Normal
Fibrinogen Low Abnormal
BIAS
2,61%
CV%
Sigma BV
SIGMA CLIA/CAP
TEA
13,6 20
Median
5,88
1,87
2,96
5,49
2,0
3,17
Min-Max
3,75-8,04
1,37-2,93
2,11-4,04
5,05-7,01
1,57-2,18
2,48-3,44
SIGMA 3-6
(%)
41,7 75
VII
Normal
Low Abnormal
VIII
Low
Abnormal
vW:Ag
BIAS
14,89%
12,08%
13,7 %
cv%
Median
(Min-Max))
4,61
(2,96-6,85)
4,98
(3,18-8,46)
6,32
(4,11-10,93)
7,96
(4,71-15,35)
3,39
(1,85-7,11)
3,68
(2,35-6,19)
TEA BV
10,7
8,9
8,8
SIGMA 3-6
(%)
Aim
The aim of the present study was to calculate Sigma for several tests of the Haemostasis Laboratory, using CLIA, CAP and BV TEA requirements, comparing the performance obtained.
Methods I
We calculate the BIAS as the mean BIAS obtained in the last 4 EQC surveys in which our laboratory participated. In all of these surveys the performance of our laboratory was successful., and all test results were within 2SDI from the mean of the peer group. We calculated the cv% of Prothrombin time(PT), activated partial thromboplastin time (APTT) and fibrinogen (FIB), factor VII, VIIII, vW:Ag, PC, PS and AT for each month of 2012 from the Internal Quality Control at two levels normal and low abnormal. During the period the general precision of the laboratory ranged from
We also calculated each month SIGMA for every level of control materials using CLIA, CAP or BV requirements as TEA. PC
Normal
Low Abnormal AT
Low
Abnormal
Free PS
BIAS
5,9%
5,02%
8,46 %
cv%
Median
(Min-Max))
2,36
(1,78-7,18)
2,92
(2,0-7,42)
3,69
(2,45-5,14)
11,85
(3,55-16,71)
3,63
(2,4-6,55)
3,86
(2,33-8,39)
TEA BV
18,7
8,3
20,3
SIGMA 3-6
(%)
83,3 75
58,3
Conclusions
SIGMA metric, widely used for chemical determinations, seems not to be applicable for most of the tests in the haemostasis laboratory. It is particularly true when the BV is used as TEA, because in our hands only free protein S and Protein C reached some acceptable SIGMA values, but no coagulation test, nor chromogenic AT or immunoturbidemetric vWF Ag have reached SIGMA acceptable requirements, even when the precision and inaccuracy of the laboratory is correct.
SIGMA was calculated as (TEA % – BIAS %) CV
References
- Wetagard JO. Six Sigma Quality Desing & Control. Desirable Precision and Requisite QC for Laboratory Measurement Process, 2001