Re: absolute counts - a side issue

Joseph Webster (
Fri, 28 Feb 1997 18:24:58 +1100

At 09:47 AM 27/02/97 -0600, Keith Bahjat wrote:
>Considering that the FACScan/FACSort/FACSCalibur instruments aspirate an
>unknown volume while the tube is being placed on the SIP and again as the
>tube is being taken off, is this method actually clinically accurate
>(i.e.,. comparable to a hematology analyzer)?

The "aspiration of unknown volume" problem IS preventable!

The sample uptake assembly in these instruments is actually two
concentric tubes; the inner carries the cell suspension into the
instrument, the outer is a drip catcher to suck away the backflush.

Simply remove the outer layer of the uptake tube and the sheath
fluid backflush is no longer sucked away, neither is the sample.

Of course there are many implications to this!
To name a few:
You need to catch the drips, else your bench gets even more messy..
Is that dripping fluid safe? (depends on your samples,
I would NOT recommend this in most clinical settings)
You CAN work with very small sample volumes...

Like most machinery, the standard instrument as delivered can often
be easily modified to do a particular job better - Provided you look
carefully at implications and side-effects.

Cheers, Joseph.

Joseph Webster
Flow Cytometry Facility
Centenary Institute

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