GC/MS vs LC/MS

[emd123]

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For confirmation testing, are the two equal? The GC/MS lab I have been using takes 7-9 days to return results. Another company is trying to convince me to switch to LC/MS which they claim is just as accurate and can return results in 2 days. I can't find much Pain specific data on this except this from Pain Physician which is a letter from those associated with the manufacturer:

http://www.painphysicianjournal.com/2010/january/2010;13;93-94.pdf

I want the most accurate results, but I want them back as fast as possible.

Thoughts?

 

[Dipipanone]

As a former mass spectrometrist with extensive experience working in an analytical lab, I will chime in with my two cents...

The important thing to realize is that gas chromatography (GC) and liquid chromatography (LC) are similar chromatographic techniques used to separate analytes. In this particular instance, the analytes are active pharmaceutical molecules and their respective metabolites. Directly following the separation, the volatalized eluent (GC) or liquid eluent (LC) passes directly into the mass spectrometer. This is where the actual identification of the molecules occur. The MS determines the mass to charge ratio of all analytes conatined within a patients specimen. The patients results are then comapered to a standard injection which is used to calibrate the instrument every morning. This reference standard depends upon the test ordered and will contain all the compounds from a certain class of drugs - i.e. benzodiazepienes, opioids, etc. This is how a positive result is generated. From an analytical chemistry standpoint, this is about as specific and sensitive as it gets....

To make a long story short, both of these techniques are comparable and appropriate for the intended purpose. The take-home message is that post-separation, the actual identification of the drug or metabolite is being performed in the same manner - via MS. In fact, with a little sample preparation, you could eliminate the GC or LC separation, and infuse directly into the MS.

While the turn-around times for the tests are different, both methods are likely performed in under an hour...

Please dont hesitate to let me know if you have any more questions...

 

[Aether2000]

Agree. Functionally they are similar. There is a theoretical advantage in accuracy using a gas column given the rapid transport and less residual sample remaining on the column, but this all depends on how fast the samples are being processed on the LC/MS. The electron beam causes ionization of the parent molecule but also causes molecular fragmentation into defined charged fragments, that then pass through a dipole or quadrupole mass spec and the pattern impacts onto a collector screen. The standard patterns are digitally encoded into the computer software so when a pattern of parent + charge fragments impact at specific points at certain intensities, the computer recognizes these. Using a second MS in the stream is a technique that creates a 99.99% accuracy. Only inaccuracies are seen if there are new drugs eg antibiotics, for which the standard patterns have not been determined nor encoded into the recognition software.

 

[Jcm800]

I am confused. I thought flux capacitor was the main difference. If the sample speed gets to 88 miles per hour, things get very very tricky...

As a former mass spectrometrist with extensive experience working in an analytical lab, I will chime in with my two cents...

The important thing to realize is that gas chromatography (GC) and liquid chromatography (LC) are similar chromatographic techniques used to separate analytes. In this particular instance, the analytes are active pharmaceutical molecules and their respective metabolites. Directly following the separation, the volatalized eluent (GC) or liquid eluent (LC) passes directly into the mass spectrometer. This is where the actual identification of the molecules occur. The MS determines the mass to charge ratio of all analytes conatined within a patients specimen. The patients results are then comapered to a standard injection which is used to calibrate the instrument every morning. This reference standard depends upon the test ordered and will contain all the compounds from a certain class of drugs - i.e. benzodiazepienes, opioids, etc. This is how a positive result is generated. From an analytical chemistry standpoint, this is about as specific and sensitive as it gets....

To make a long story short, both of these techniques are comparable and appropriate for the intended purpose. The take-home message is that post-separation, the actual identification of the drug or metabolite is being performed in the same manner - via MS. In fact, with a little sample preparation, you could eliminate the GC or LC separation, and infuse directly into the MS.

While the turn-around times for the tests are different, both methods are likely performed in under an hour...

Please dont hesitate to let me know if you have any more questions...

 

[emd123]

I am confused. I thought flux capacitor was the main difference. If the sample speed gets to 88 miles per hour, things get very very tricky...

That's what I tried, too, and I was transported back to 1985, and I was frightened, by the feathered hair, women with leg warmers and grown men with red leather Michael Jackson jackets, and all the Pain doctors driving Lamborghinis.....

 

[Ducttape]

I am confused. I thought flux capacitor was the main difference. If the sample speed gets to 88 miles per hour, things get very very tricky...

you mean we are going to see some serious s#$t?

 

[deleted314957]

For confirmation testing, are the two equal? The GC/MS lab I have been using takes 7-9 days to return results. Another company is trying to convince me to switch to LC/MS which they claim is just as accurate and can return results in 2 days. I can't find much Pain specific data on this except this from Pain Physician which is a letter from those associated with the manufacturer:

http://www.painphysicianjournal.com/2010/january/2010;13;93-94.pdf

I want the most accurate results, but I want them back as fast as possible.

Thoughts?

My perspective as a boarded clinical pathologist: as a confirmation test specificities are essentially equivalent. go with whoever provides the best (tat) and most cost effective service. make sure the lab has all the appropriate accreditions (clia, cap, etc) and that the medical director is not a urologist ( or some-such)

 

[ghost dog]

you mean we are going to see some serious s#$t?

This takes me back... I saw this movie about 8 times in the theatre when I was a kid. My favorite childhood movie !

 

[Ducttape]

This takes me back... I saw this movie about 8 times in the theatre when I was a kid. My favorite childhood movie !

aw crap... childhood movie?

i was in med school when it came out...

 

[NEPain]

Hey, while on the topic of UDT. I've read every article I can find on this topic and they always address adulteration and dilution superficially. Other than seeing it happen, is there a way to know for sure that a specimen was adulterated or diluted? Is there a creatinine level that is below human ability that would allow me to tell the patient that I KNOW they diluted the urine?

 

[Ducttape]

i get creatnine levels with my UDS. <5.1 mg/dl - "Inconsistent with Urine... adultaration attempt likely".

 

[Jcm800]

This takes me back... I saw this movie about 8 times in the theatre when I was a kid. My favorite childhood movie !

which he means he is really young, because it didnt come to canada until like 1998...

 

[CerebralEdema]

Hey, while on the topic of UDT. I've read every article I can find on this topic and they always address adulteration and dilution superficially. Other than seeing it happen, is there a way to know for sure that a specimen was adulterated or diluted? Is there a creatinine level that is below human ability that would allow me to tell the patient that I KNOW they diluted the urine?

Temperature should be 32-38C at POS testing, (if you do POS testing)
pH: <4 or >8 is not physiologic.
And SG: <1.002 or >1.02 is out of range.

The classic scheme that a drug abuser will use is to make a small crack in the UDT plastic collection cup or lid... usually on the edge where the lid meets the cup... so during transport the urine leaks out and boom, no sample to test since its all floating in the sealed bag.

Sometimes, if you shake the sample and see lots of soap-like bubbles it probably means they added the hand soap in your office bathroom to try to adulterate the sample.

 

[ghost dog]

which he means he is really young, because it didnt come to canada until like 1998...

Oh snap !