Introduction

According to the order n°2010-49 relative to Medical Biology, all Medical Biology Labs have to accredit more than 50% of their activities before 2016.
With a view to accrediting Neolab, the standard NF ISO EN 15189 requires a verification of all methods used in the lab. Microbiology is one of the sectors to substantiate; I realized analyses to reach this verification. So a linearity study of red corpuscles was made on the robot iQ200® which is a device of urinary cytology.
The results have to be in concordance with those of the application engineer; otherwise the method isn’t certified.

Experimental conditions

The iQ200 is a urinary cytology robot, using flow cytology by taking pictures which allows a significant time benefit. After taking pictures, a software called “AutoParticle Recognition” detects, classifies and quantifies particles.
In order to analyze the linearity of red corpuscles, we used tubes with circle bottom of 10 mL, some fresh samples of urine concentrated in red corpuscles at 1000 particles / µL( be careful not to put the samples in the fridge to avoid the apparition of crystals) and pipette adapted for following dilution (see figure 1).
Then pass one rack in the iQ200, be careful to respect the order of the samples from the less concentrated to the more concentrated.
Finally, pass a second same rack.

Results

The linearity of a method is its ability to obtain results directly proportional to the concentration of the substance analyzed.
Two series of measures were made in order to have an average of these results. We calculated differences, concordances and agreement on slope and points. If those agreements are smaller than 20%, the verification was succeeded.
The figure 2(A) shows the result of those calculations and figure 2(B) shows the linearity on a graph. The linearity of red corpuscles is certified since all agreements are inferiors to 20%. Besides, by analyzing the graph, the correlation coefficient (R²) is about 0, 9989 which is really close to 1 so the linearity is confirmed on the graph too.

Conclusion

The linearity of red corpuscles was certified successfully since all the agreements were inferiors to 20% and the correlation coefficient was close to 1.

The dilution of samples

A) Necessary calculations to certify the linearity
B) Graph represents the linearity of red corpuscles

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