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Question for Runner Girl


calypso
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Runner Girl or anyone else who might know the answer to this:

I had the plasma free metanephrine test drawn a few weeks ago. However, when the test came back, it said I had an "interfering substance" in my blood. I have not been able to reach anyone at the endocrinologist's office who ordered it, so I am wondering what kind of substance that would be ... the only drug I am taking is a beta blocker. Do you know if you can have this test drawn while on beta blockers?

Or maybe I AM being drugged after all ...

Amy

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Hi, Amy. The beta blocker shouldn't be a problem. In fact, as far as I know, the only inteferring substance for the PFM assay is actually Tylenol - or any substance containing acetaminophen, the active ingredient in Tylenol. Any chance you popped a Tylenol for a headache or took cough medicine before you test???

Other substances (caffeine, alcohol, etc.) do not interfere, but rather can cause falsely elevated readings.

The following is from Quest Labs:

Code: 37745 METANEPHRINES, FRACT., FREE, PLASMA

Performing Lab:

Clinical Significance:

Reference Ranges:

Preferred Specimen: 5 ML OF FROZEN EDTA PLASMA (LAVENDER-TOP)

PATIENT PREPARATION: DISCONTINUE EPINEPHRINE AND

EPINEPHRINE-LIKE DRUGS AT LEAST 1 WEEK BEFORE OBTAINING

THE SPECIMEN. THE PATIENT MUST REFRAIN FROM USING ACETAMINOPHEN FOR

48 HOURS BEFORE THE SPECIMEN IS DRAWN.

THE PATIENT MUST REFRAIN FROM USING CAFFEINE, MEDICATIONS,

AND TOBACCO AND FROM DRINKING COFFEE, TEA, OR ALCOHOLIC

BEVERAGES FOR AT LEAST 4 HOURS BEFORE THE SPECIMEN IS DRAWN.

Alternate Specimens:

Minimum Volume:

Specimen Container: PLASTIC SCREW-CAP VIAL

Transport Temperature: FROZEN

Specimen Stability: REFRIGERATED: 30 DAYS

FROZEN: 30 DAYS

Reject Hemolysis:

Reject Lipemia:

Reject Thaw/Other:

Methodology: LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY (LC-MS/MS)

Setup Days:

Setup Times:

Turnaround:

CPT Code(s): 83835

Please let me know if you have any other questions!

Best to you,

RunnerGirl

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That's really odd. I never take Tylenol (except a couple times a couple years ago, when I was pregnant). I did talk to my endo's nurse and he said that the metanephrine in my blood "could not be quantified properly" due to an interfering substance, but he didn't know what that substance was because the lab didn't list it. If I have a substance in my blood that I don't know about, I sure would like to find out what it is. I may call the lab and ask. Thanks for your extensive knowledge in this area!

Now off to pick up the pee jugs so I can collect 24-hour urines in this test's place.

Amy

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Ah, yes, those lovely orange pee jugs! I remember them well! (Note to others using the fridge: This is NOT orange juice! :-))

As regards you PFM test, it does seem very odd that they indicated an inteferring substance when you didn't take any acetominaphen-containing products. I've met some of the top NIH pheo researchers and that's one of the several reasons they consider the plasma free metanepherine test the 'gold standard' for ruling in/out pheo - so few substances can interfere.

Your lab probably already gave yout these instructions for the 24-hour urine test, but just in case, you may want to check out:

http://my.webmd.com/hw/heart_disease/hw6078.asp#hw6141

If you are able to get more info from your lab on the PFM test, I'd be VERY curious to know what they say about the inteferring substance. In the meantime, I'll check with some of my pals on the pheo boards to see if they know of any other substances that can interfere.

Take care,

RunnerGirl

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