NO SUCH THING AS THE BEST TECHNIQUE
challenging due to changes in the consistency of the matrix.
“
...subaliquoting can become even more ”
MICROSAMPLING: THERE IS NO SUCH THING AS THE BEST TECHNIQUE
BY HANS STIELTJES AND TOM VERHAEGHE, JANSSEN RESEARCH AND DEVELOPMENT, BELGIUM
In a previous commentary in early 2015, I discussed the use of a non-capillary microsampling technique for good laboratory practice (GLP) in non-clinical studies [1]
. One of the messages
I received was that the choice of sampling materials is important to attain good quality data, because of the smaller sampling volumes. In this commentary, additional data relevant for a capillary microsampling (CMS) technique is presented. Furthermore, the benefit of having multiple microsampling techniques in the lab is discussed; however the focus remains on ‘wet plasma’ sampling procedures.
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An important limitation to non-capillary microsampling as previously described is that accurate pipetting of small volumes (10 µL) is conducted by the animal technicians at the sample collection site and outside of the control of the bioanalyst. Although this was tested to be feasible, it is difficult to let go of the control over this pipetting in the in-vivo group. Adding QC samples to monitor the pipetting performance of the biotechnicians, on a daily basis or per study, was not considered practical in the hectic environment of sampling multiple time points from multiple animals. Performing accurate pipetting at the bioanalysis lab, along with QC samples, is more in line with generally accepted bioanalytical procedures for regulated studies.
Moving the entire sample aliquoting phase to the bioanalytical lab was however not considered feasible either. Although it would be possible to collect ‘all’ plasma and take an accurate aliquot from this at a later stage, this was rejected as well. Accurate pipetting of a small sub aliquot from an already small plasma volume is also challenging. Once a small plasma volume, especially from rodents, has undergone a freeze-thaw cycle, sub aliquoting can become even more challenging due to changes in the consistency of the matrix.
The above does not mean that the non-capillary microsampling technique cannot be applied with sufficient quality. While still suitable for early rodent studies, it is a matter of ‘proof of quality’ that may make it less suitable for supporting GLP studies. This was one of the reasons to move to CMS, which by now is considered to be a far easier technique than the non-capillary microsampling approach.
Also with CMS one must be prudent of material use. There are two approaches for CMS, as explained in several publications [2,3] O [2]
and presentations [4,5,6] . In the approach of Johnsson
, or Vitrex technique, a 32 µL volume of blood is collected into a capillary coated with an anti-coagulant, mostly K2EDTA. Vitrex or Hirschmann, to name two, provide these hematocrit capillaries.
After collection, one end of the capillary (the end that has been in contact with the blood drop) is sealed with a wax plug. After centrifugation, the capillary is cut just above the layer between blood cells and plasma. An accurate plasma volume is transferred to a small volume, non-coated end-to-end capillary.
www.bioanalysis-zone.com
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