Re: failed methotrexate solved!!!
From: art fougner, md (evsono@pipeline.com)
Tue Jun 13 07:51:59 2000
can't help with the prior negs but this case illustrates the old adage -
"before calling the repairman, first check the plug."
glad things worked out ok.
art
At Mon, 12 Jun 2000, Shayne wrote:
>
>Thank YOU for your help esp those who suggested the assay problem... I
>had excluded that on the basis of her prior neg serum beta's the
>explanation I received from our lab can be found below. I still am
>unsure why she has previous neg results
>Shayne Mora Bellingham Wa
>
>Dear Dr.Mora,
>Your patient N.Z. had quantitative hCG levels run at our laboratory
>using
>the Abbott Axsym Total B-hCG assay (Abbott list number 7A59). This
>assay
>uses a monoclonal mouse capture antibody and goat polyclonal tag
>antibody,
>with bovine and goat serum in the sample diluent to block interference
>from
>anti-goat antibodies that may be present in the patient sample.
>
>Coll. Date mIU/mL hCG Interp
>5/27/98 5 Equivocal
>6/1/98 3 Negative
>6/9/98 2 Negative
>8/25/98 2 Negative
>10/26/98 2 Negative
>3/31/00 153 Positive
>4/3/00 143 Positive
>4/7/00 43 Positive
>4/14/00 60 Positive
>4/17/00 90 Positive
>4/20/00 74 Positive
>4/25/00 81 Positive
>4/28/00 97 Positive
>5/2/00 94 Positive
>5/4/00 70 Positive
>5/10/00 61 Positive
>5/17/00 46 Positive
>5/25/00 59 Positive
>5/30/00 87 Positive
>6/2/00 60 Positive
>6/9/00 60 Positive
>
>I was able to retrieve the last two serum samples from refrigerated
>storage
>and test them with the Hybritech ICON II qualitative hCG assay
>(distributed
>by Beckman-Coulter) utilizing mouse monoclonal antibodies for both
>capture
>and tag. The results were negative at the stated 25 mIU/mL sensitivity
>of
>the test. This is a visually read test and there did not appear to be
>any
>hCG reactivity, which in my experience indicates <10 mIU/mL hCG even
>though
>the FDA-approved sensitivity is listed as 25 mIU/mL.
>Hybritech
>Coll. Date mIU/mL hCG Interp
>6/2/00 <25 Negative
>6/9/00 <25 Negative
>
>I also performed some experiments on these two samples using the Abbott
>Axsym instrument and reagents used to generate the original results. In
>one
>experiment, I used the instrument's on-board dilution capability to use
>the
>reagent kit's specimen diluent to perform a 1:10 dilution. In another, I
>used specimen diluent taken from an Abbott Axsym CK-MB kit containing
>goat
>serum to perform a manual 1:2 dilution of N.Z.'s last two serum samples:
>
>Coll. Date mIU/mL hCG, neat mIU/mL hCG, on-board 1:10 dilution
>mIU/mL hCG, x2 dilution with goat serum
>6/2/00 60 Undetectable, <2 mIU/mL
>Undetectable, <2 mIU/ML
>6/9/00 60 Undetectable, <2 mIU/mL
>Undetectable, <2 mIU/ML
>
>The patients serum was tested for Rheumatoid Factor (one possible cause
>of
>false positive immunoassays) and found to be negative. It therefore
>appears
>to be highly probable that the patient's false-positive hCG levels were
>caused by heterophile and/or anti-goat antibodies in her serum present
>in
>excess of the capacity of the specimen diluent's ability to block it.
>The
>mechanism for this interference is unknown -- it seems improbable that
>an
>antibody to the tagged goat anti-hCG would cause it to bind to the
>capture
>antibody or otherwise prevent it from being washed away with the unbound
>tag. Nevertheless, if you add enough goat serum the interference goes
>away,
>so anti-goat antibodies in the patient serum are the most likely
>suspect.
>
>This sort of case was recently in the news:
>http://www.postintelligencer.com/local/canc19.shtml
>
>All immunoassays are subject to this same interference. Just within the
>past
>month, customers using a competitor's assay (Roche) were warned of a
>similar
>problem: http://www.biofind.com/rumor/rumor_viewmessage.asp?msg_idA302
>
>We saw some problems with our Troponin assay (but not hCG at that point)
>and
>sent this announcement to all the physician offices last November:
> <<Chem Link 13 Lipase&interference.doc>>
>
>Thank you for bringing this case to our attention. I will be discussing
>it
>with our medical director tomorrow. Please give me a call if you have
>any
>further questions or concerns.
>
>Gary Sandberg MT(ASCP) SC
>Chemistry supervisor
>NorthWest Regional Laboratory
>St.Joseph Hospital
>Bellingham, WA
>738-6330 x2961
--
art fougner, md
A series of 1000 cases begins with but a single anecdote.
