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I have a question about handling BLQs for a regular NCA analysis using rich plasma conc data.
I learnt that there are methods to handle BLQs in NONMEM for POPPK analysis (e.g. M1 to M7), but
how do you handle BLQs in NCA analysis, especially if we have BLQs in between Tmax and Tlast?
Even though BLQ value is not equal to 0, I feel comfortable substituting the value to 0 before Tmax
and after Tlast (not sure if this is accurate), but how about the BLQs in between Tmax and Tlast?
substitute those values to 0? or
exclude those values or assign a missing value?
or should I impute those values with LLOQ/2?.
Appreciate your inputs in this regard.
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First, I agree with your BQL rule befure Tmax. For BLLOQ data after Tmax, normally MISSING (OR ND)
will be used. In most of the situation, it should not influence your terminal phase slope estimation
if you have proper sampling time points. Sometimes, LLOQ/2 (OR LLOQ/3) might be used for the first
BLLOQ data after Tmax and Missing for the following BLLOQ data. To me, it is difficult to tell why
you select LLOQ/2 not LLOQ/3, vise versa. So, I prefer to using Missing for all BLLOQ data after
Tmax. However, you should also use your judgement sometime and compare CT curves between different
subjects because of irregular concentration time curve, especially when the concentration is nearby
Tao Liu BSc
Center for Translational Medicine
University of Maryland, Baltimore
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