This correspondence has certainly taken me back in time! In the early
1980's (I think) we were struggling to reach consensus with our clinical
colleagues on the 'best' way of doing the test and reporting it, and,
being on the spot, more or less, I wrote to Bill Liley for advice. I
think that it was he who pointed out that his original graph was being
redrawn, not always correctly - for example, in the 2nd Ed of Tietz the
graph shown ("after Liley") has both axes on a linear scale, which
should have meant the zones were indicated by curves. Transferring to
log-lin paper (as originally) creates the straight-lined zones, and this
appears in the 3rd edition. We used CHCl3 extraction for a while, and
centrifuged to reduce turbidity, but it was never a test that I felt
altogether comfortable about. We presented the results on the Liley
chart, and on the "Whitfields Action Line" chart (Amer J Obstet Gynae
(1970) 108:1239-44).
Chris Lovell-Smith
Clinical Leader and Chemical Pathologist
Healthlab Otago, Dunedin Hospital, Dunedin, NZ.
Phone 64 3 474 7925 Fax 64 3 474 7637
-----Original Message-----
From: Frederic Cotton [mailto:[log in to unmask]]
Sent: Wednesday, 7 February 2001 21:39
To: [log in to unmask]
Subject: Re: Amniotic fluid bilirubin reporting
I think the article I suggested in my last message could interest all of
you: Spinnato JA et al. Obstet & Gynecol 1998;92:441-5.
Firstly, Spinnato recommends the chloroform extraction procedure which
eliminates all interferences from hemoglobin or turbidity (a better
solution
than correction, to my opinion) [Spinnato JA Am J Obstet Gynecol
1991;165:1030-5].
Secondly, he compares the Queenan and the Liley methods. In fact, both
graphs have been constructed differently. The Queenan method is based on
"normal values": mean OD + 2SD of normal pregnancies [Am J Obstet
Gynecol
1993; 168:1970-6] while the Liley method was made studying rhesus
sensitized
pregnancies [Am J Obstet Gynecol 1961;82:1359-70].
Spinnato clearly shows that the Liley method is superior because the
Queenan
method frequently overestimates the risk.
Frederic Cotton
Clinical Pathologist
Clinical Chemistry Department
Hôpital Erasme - Université Libre de Bruxelles - Belgium
----- Original Message -----
From: Andrew Lyon <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 07, 2001 6:45 AM
Subject: Re: Amniotic fluid bilirubin reporting
> RE: Oxyhemoglobin correction?
>
> Coincidently I was reviewing our amniotic fluid bilirubin method
earlier
> this week and I noticed an un-referenced statement in an appendix
that:
> When oxyhemoglobin is present, then 5% of the OD415 can be
substracted
> from the OD450 to produced a corrected OD450 result.
>
> Michael was the first to mention use of this correction for
> oxyhemoglobin inteference in this discussion. Our current amniotic
> fluid bilirubin method also measures oxyhemoglobin at OD415,and we
> monitor that wavelength for potential interference but do not
routinely
> correct OD450 the results with the factor.
>
> I am considering implementing the oxyhemoglobin correction factor.
> I suppose I could test the validity of the 5% of OD415 factor easily
> enough.... but could someone direct me to a publication that describes
> an evaluation of the correction factor?
>
> I am concerned that light scattering particulates in turbid samples
> (that do not centrifuge down) may lead to a falsely increased
> "correction factor" and subsequently lower OD450 results.
>
> regards, Andrew
>
> Andrew Lyon
> Calgary, AB.
>
>
> [log in to unmask] wrote:
> >
> > We report OD450 corrected for oxyhaemoglobin and a calculated
bilirubin.
> > Some years ago we stopped using the graph of Liley due to the
limited
range
> > ( I think it started at 20 something weeks to 40 weeks) -
transplacental
> > transfusions can be performed from about 18 weeks and the data
published
by
> > Queenan et al. Am J Obstet Gynecol 1993:168; 1370-6 is more up to
date
> > (1993 vs 1961). The test is done is exactly the same way as before
but
is
> > plotted on a different graph.
> >
> > Michael Freemantle
> > Biochemistry Dept
> > Sullivan Nicolaides Pathology
> > Taringa Ph 07 3377-8638 Fax 07 3870-5989
>
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