# PharmPK Discussion - BLOQ data

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• On 16 Aug 2002 at 13:55:53, Rostam Namdari (chista90.-a-.yahoo.com) sent the message
`Dear Colleagues,Couple of months ago when we were discussing how tohandle BLOQ values for TK/PK analysis almost everyoneshut down the idea of using zero for BLOQs because intheory there are some drug still in the system,problems with fitting log of zero and underestimatingthe mean.  Ignoring them dose not solve the problem asmay result in overestimating the mean value.1) Did we ever discuss using half of LOQ? What are theadvantages and disadvantages of this approach?  Iwould appreciate your input.2) How do we deal with a situation when we have allthe measurements (say data from all three animals) forthe last two time points (say 48 h and 72 h) as BLOQ?If we assign a value equal to LOQ/2 then we startgetting a flat line and a false long t1/2.Roger: Can we apply your method (USC*PACK) tosituation where we have background concentrations(radioactivity data) and not quite LOQs?  Pleaseforgive me if this is an inappropriate question tobegin with.Rostam`
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• On 16 Aug 2002 at 18:16:57, Roger Jelliffe (jelliffe.aaa.usc.edu) sent the message
`Dear Rostam:          Thanks for your note. I would think it would work fine. Justsubtract out the background, let the results be either positive ornegative, and find the mean and SD. Then you have the SD of a zero. Then,using the working assay, you can, with the other values (which should alsohave the background subtracted out, ba able to determine the SD of anymeasurement, using the error polynomial.          On the other hand, if you are using radioactive counts, you shouldbe able to determine the error of the counts directly also, and use thatfor each of your samples, to find the SD of the counts for each sample.When you get down to the background, you can also determine the SD of therepresentative background count.Does this help? I look forward to hearing from you.Very best regards,RogerRoger W. Jelliffe, M.D. Professor of Medicine,Division of Geriatric Medicine,Laboratory of Applied Pharmacokinetics,USC Keck School of Medicine2250 Alcazar St, Los Angeles CA 90033, USAemail=  jelliffe.at.usc.eduOur web site=  http://www.lapk.org`
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