LONG TERM IMPRECISION: HOW TO CALCULATE

Introduction

            The monitoring of long term laboratory imprecision is very important for patient management, especially in the follow up for the response to treatment based on the laboratory data. Currently, the long term imprecision is based on the combination of the intermediate CV as CV= √ (CV₁²+CV₂²+ CV₃² +….). This formula provides bigger CV  compared to the generated CV by the analyzer for the same duration.

            The aim of this study is to determine alternative method in calculation for the long term imprecision compared to the generated CV in the same duration.

Method

            The Albumin quality control data, Level 1 and Level 2 on the Architect c8000 analyzer for six months ( July, August, September, October, November and December  2012) were used in this study. The analyzer generated the mean, SD and CV for the last six months duration and on monthly basis (July to December respectively). The monthly mean, SD and CV were entered in the excel work sheet for calculation of the long term imprecision in two methods:

i.                    Based on the combination of monthly CV and

ii.                  Based on the combination of the monthly variance.

The value of the total CV obtained in the above method was compared to the generated CV for the last six month (July to December).    

Results

            The results from the experiment are as the  following :

1.                 Automated generated  Total CV by the analyzer for the duration of July to December

 

DURATION	LEVEL 1				LEVEL 2
	N	MEAN (g/l)	SD	% CV	N	MEAN ( g/l)	SD	% CV
July to Dec	231	40.54	0.827	2.04	234	24.7	0.61	2.46

 2.         Monthly data (July to December)

MONTH	N	LEVEL 1			LEVEL 2
		MEAN (g/l)	SD	CV	MEAN	SD	CV
JULY	2	41	0	0.00%	24.5	0.707	2.89%
AUGUST	57	40.54	0.569	1.40%	24.745	0.440	1.78%
SEPT	57	39.72	0.526	1.32%	24.18	0.563	2.33%
OCT	54	40.333	0.476	1.18%	24.91	0.446	1.79%
NOV	52	41.481	0.504	1.22%	25.245	0.434	1.72%
DEC	9	41.556	0.527	1.27%	25.111	0.333	1.33%

 3.         Imprecision calculation

       

Imprecision calculation (six month)	Level  1 QC	Level 2 QC
Based on the monthly CV	2.86%	4.99%
Based on the monthly Variance	2.04%	2.46%
Automated generated by analyzer (six month)	2.04%	2.46%

      

The results showed that CV generated by automated analyser based on the QC data July to December were 2.04% for level 1 and 2.46% for level 2. The CV calculated based on the combination of monthly CV from July to December on the same QC data were 2.86% for level 1 and 4.99% for level 2. On the other hand, when the CV is calculated based on the combination of monthly variance on the same QC data, it was found that CV for level 1 was 2.04% and level 2 was 2.46%.

Conclusion

            Based on this study, it was found that the long term CV calculated based on the combination monthly variance gave  comparable result to that of  automatically generated CV  by the analyser where as combination of the monthly CV gave much bigger CV. Therefore, it can be concluded that the CV calculated by monthly variance is more reliable compared to the combination of the monthly CV.  

PERFORMANCE OF COBAS 8000 : HOW TO DETERMINE

 

Introduction

The precision of laboratory results is important to help clinicians to diagnose and to monitor the patient treatment. The automated analyzer is used for analysis of the patient samples for routine chemistry and urine tests, immunology and immunoassay. The instrument must be precise to deliver the patient results. This is very important in patient management.

METHODOLOGY

PRELIMANARI PRECISION

·         Level 1 and level 2 quality control recommended by manufacturer were run triplicate per day for five day.

·         The mean, variance, standard deviation and coefficient variation experiment were calculated for repeatable and intermediate.

·         The repeatable and intermediate coefficient variation were compared with the repeatable and intermediate coefficient variation manufacturer followed by The Clinical Laboratory Standard Institute (CLSI EP 10).

If unacceptable for both or other one perform ,verification precision

 

VERIFICATION PRECISION

 ·         The standard deviation for repeatable manufacturer (SD_mnf) and/or standard deviation

       intermediate manufacturer(TSD_mnf) were calculated based on mean experiment and  

       coefficient variation manufacturer.

·         The standard deviation for repeatable and/or intermediated manufacturer were compared with the standard deviation experiment (repeatable and/or intermediate where applicable) followed by The Clinical Laboratory Standard Institute (CLSI EP 15)

·         If unacceptable, the troubleshooting were perform and repeat the preliminary precision

 

Results

The achievement of the analyzer for routine chemistry and urine tests, immunology and immunoassay for the level 1 QC based on the coefficient variation manufacturer claim were 54% for repeatable and 78% for intermediate at the preliminary precision. 46% of the level 1 QC for repeatable and 22 %  of the intermediate were acceptable at the verification precision.

For the level 2 QC results, the performance based on the coefficient variation of manufacturer claim is 56% and 77% for intermediate.  Therefore, 44% of the;level; 2 QC for repeatable and 23% of the intermediate were acceptable based on the verification precision.

Conclusion

Based on the studies, all the results of the routine chemistry and  urine tests, immunology and immunoassay are precised for patient management as long as maintenance schedule, the procedure of the pre-analytical as sample collection, transportation, time receiving and processing of samples are followed.