I was fired. Was I wrong?
Posted: Wed Jan 23, 2019 4:16 am
Walked in today and was walked out. Toxicology lab has been losing samples for a while now I suspect it was largely fiscal. Whatever.
What I want to pick your brains about is the reason they gave, was that I "failed" my 'training' in relation to processing properly LC/MS/MS chromatography data.
A month ago I was given a number of previously reported samples to analyze independently with Masshunter (Agilent LCMS software), to be later 'graded' against the reported values. I used the same methods they did and generated samples with values that were based on the calibration curve generated that day of the run. Basic stuff. However, I 'failed' to follow a particular practice they have been using, and I feel it is yielding in about 1 in 10 samples going out with false negative results, daily.
What I would like to do is for you to tell me, who is correct in the following scenario:
LCMS Curve is generated using increasing concentrations of analytes and their deuterated internal standards. Levels 1-9
The L1 is considered their Lower Limit of Detection
The L2 is considered the cut-off.
Any sample's value, with proper chromatography, above the cut-off is considered a positive result. Any below the cut-off is considered negative.
Basic stuff so far.
The calibration curve plots the values of analyte's response, in relation to the internal standard response. In theory the internal standard is added in equal concentration in all samples.
So, in essence, we are generating values based on the RATIO of the response to the internal standard's response, both measured by area-under-the-curve. Which, I believe, is the whole point of using internal standards in LCMS. The idea being that by using the ratio and not just the analyte's response alone, you can help weed out the effects of ion suppression. So that if something causes a lower response to the target analyte, it will likely also happen to the internal standard. So even if a sample randomly gets half the total response as it normally "should" due to ion suppression, it will still yield a correct concentration value due to the ratio being used to make the concentration value and not just the analytes response alone.
So far am I right? I think this is still page 1 of analytical chemistry textbooks, right?
Ok, so here is where they change it up. They claim that if the sample's response is LOWER than the L2's response, that even if the calculated concentration value is above the cut-off, it is to be called negative and not positive.
So for example:
Morphine Calibration Curve's L2 Analyte Response = 10,000 with a concentration of 100. (So cut-off is 100.)
Morphine of Test Sample's Response = 8,000 with a calculated concentration of 155.
I say the 155 is correct and the sample is positive because there was ion suppression. The use of an internal standard protected this sample from being called negative because its value was made from a ratio of both.
They say, the sample, despite being above the cut-off, is negative because the analyte's response was lower than the L2's.
I feel they are totally ignoring the existence of ion suppression in LCMS by this practice and are calling samples with properly calculated values, well above the established cut-off, negative. Thus resulting in them reporting to physicians a "false-negative" result.
This is a problem because we do urine toxicology and most of our samples are for drug compliance. As in, "is Jane Doe taking her meds or selling them?" I feel that because of their random "rule", they are reporting out that people who ARE taking their meds are not. And this will result in people getting fired from their doctors and from receiving their meds because of supposed 'non-compliance' when in reality it was they were just unlucky enough to have had their sample have ion suppression.
Who is right here? I got fired for calling those test values positive. What would you do? What is your call? Literally tens of thousands of people have been effected by this 'rule'. Is is scientifically sound?
Thanks guys!
What I want to pick your brains about is the reason they gave, was that I "failed" my 'training' in relation to processing properly LC/MS/MS chromatography data.
A month ago I was given a number of previously reported samples to analyze independently with Masshunter (Agilent LCMS software), to be later 'graded' against the reported values. I used the same methods they did and generated samples with values that were based on the calibration curve generated that day of the run. Basic stuff. However, I 'failed' to follow a particular practice they have been using, and I feel it is yielding in about 1 in 10 samples going out with false negative results, daily.
What I would like to do is for you to tell me, who is correct in the following scenario:
LCMS Curve is generated using increasing concentrations of analytes and their deuterated internal standards. Levels 1-9
The L1 is considered their Lower Limit of Detection
The L2 is considered the cut-off.
Any sample's value, with proper chromatography, above the cut-off is considered a positive result. Any below the cut-off is considered negative.
Basic stuff so far.
The calibration curve plots the values of analyte's response, in relation to the internal standard response. In theory the internal standard is added in equal concentration in all samples.
So, in essence, we are generating values based on the RATIO of the response to the internal standard's response, both measured by area-under-the-curve. Which, I believe, is the whole point of using internal standards in LCMS. The idea being that by using the ratio and not just the analyte's response alone, you can help weed out the effects of ion suppression. So that if something causes a lower response to the target analyte, it will likely also happen to the internal standard. So even if a sample randomly gets half the total response as it normally "should" due to ion suppression, it will still yield a correct concentration value due to the ratio being used to make the concentration value and not just the analytes response alone.
So far am I right? I think this is still page 1 of analytical chemistry textbooks, right?
Ok, so here is where they change it up. They claim that if the sample's response is LOWER than the L2's response, that even if the calculated concentration value is above the cut-off, it is to be called negative and not positive.
So for example:
Morphine Calibration Curve's L2 Analyte Response = 10,000 with a concentration of 100. (So cut-off is 100.)
Morphine of Test Sample's Response = 8,000 with a calculated concentration of 155.
I say the 155 is correct and the sample is positive because there was ion suppression. The use of an internal standard protected this sample from being called negative because its value was made from a ratio of both.
They say, the sample, despite being above the cut-off, is negative because the analyte's response was lower than the L2's.
I feel they are totally ignoring the existence of ion suppression in LCMS by this practice and are calling samples with properly calculated values, well above the established cut-off, negative. Thus resulting in them reporting to physicians a "false-negative" result.
This is a problem because we do urine toxicology and most of our samples are for drug compliance. As in, "is Jane Doe taking her meds or selling them?" I feel that because of their random "rule", they are reporting out that people who ARE taking their meds are not. And this will result in people getting fired from their doctors and from receiving their meds because of supposed 'non-compliance' when in reality it was they were just unlucky enough to have had their sample have ion suppression.
Who is right here? I got fired for calling those test values positive. What would you do? What is your call? Literally tens of thousands of people have been effected by this 'rule'. Is is scientifically sound?
Thanks guys!