# PharmPK Discussion - Intercept and LLOQ

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• On 9 Jan 2008 at 19:39:53, LCMSMS BE (lcmsms_be.-at-.windowslive.com) sent the message
`Dear Forum,Is there any relationship between the intercept of the linear equationand LLOQ area ratio values.Thank you for sharing your experiences.Regards`
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• On 9 Jan 2008 at 10:23:53, Xiaodong Shen (shenxiaodong11.at.yahoo.com) sent the message
`The following message was posted to: PharmPKHi,Interept gives an idea how high is your blankbackgroud, which usually has something to do with theinterference. By my understanding, the LLOQ signal tothe signal of intercept needs to be above 5.Xiaodong`
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• On 9 Jan 2008 at 11:14:35, "Luis Sojo" (lsojo.aaa.qltinc.com) sent the message
`The following message was posted to: PharmPKHello,In my view, the intercept in a regression line derived from response(peak are ratio) against concentration is related to the "noise" in themethod made up of the various contributing sources of uncertainty.Mathematically, is the response at zero input, or "background" of thesystem.  Now, the type of statistical weight used during the regressionanalysis will have an impact on the intercept and on the accuracy of thecalculated concentration at the LLOQ, so once can see a relationshipbetween the intercept and the LLOQ.  I do not think there is anythingelse beyond this.Luis`
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• On 9 Jan 2008 at 18:27:18, Stanley110.-a-.aol.com sent the message
`One must be cautious assigning meaning to a y-intercept by regression.First, it may be observed but not statistically significant. It isthen ignored.It may be statistically significant but not of any practicalsignificance because we do not know if the regression curve fits at x= 0. The response vs. conc relationship in the intercept region may bedifferent from what is observed over the calibrators or standards.If it is practically significant, it is probably not a correct readingof the constant error term. That is gotten as the Total Youden Blankwhich is an independent regression.Regards,Stan AlekmanStanley L. Alekman PhDS.L.Alekman Associates Inc.`
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• On 10 Jan 2008 at 11:26:41, "Bruce Charles" (b.charles1.aaa.uq.edu.au) sent the message
`I am not sure if I have folowed the complete thread of this issue, butif using a statistical algorithm with the calibration data, e.g. OLS,you can get a (+) or (-) intercept without any "interference" actuallybeing present at all. This is by virtue of the fact that if you areusing OLS regression the LS criteria minimizes the SS of thedeviations between the data and the fitted points - This criterion isactually a variance term in disguise, and thus the largerconcentrations have more "pull" in the process of getting the best fitat the expense of the smaller values, therefore the apperarance of anintercept term in the calibration. This of course is why variousweighting schemes are used, e.g. 1/X or 1/X**2, the latter probablybeing the first to try as it more closely resembles the SS.CheersBC`
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• On 10 Jan 2008 at 15:56:58, "Ed O'Connor" (eoconnor.-at-.matrixbioanalytical.com) sent the message
`The following message was posted to: PharmPKThe intercept is an extrapolated or theoretical value.The LLOQ is a fixed point- based on concentration- it is notextrapolated or theoretical.   It is proven by having met performanceacceptance criteria.The general relationship is intercept < LLOQ where the response isdirectly proportional to the concentration and intercept > LLOQ wherethe response is inversely proportional to the concentration.--Ed O'Connor, Ph.D.Laboratory DirectorMatrix BioAnalytical Laboratories25 Science Park at YaleNew Haven, CT  06511Web:     www.matrixbioanalytical.comEmail:    eoconnor.-at-.matrixbioanalytical.com`
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