When you do a study, you have some inclusion and exclusion criteria. here, it seems that the exclusion criteria mention patients with these levels of serum bilirubin and creatinine. The word that bothers you is "assassee" and this is the "baseline" level with which future levels will be compared during the study or during a follow-up study.
Or, these "baseline serum levels" are indicative of some renal or liver impairment and they do not wish to include these patients in the study for those reasons.

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Note added at 23 mins (2010-08-05 19:15:42 GMT)
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Baseline serum creatinine levels and body mass index were collected from the ... longer for patients with baseline creatinine < or =0.6 mg/dL (p = .058). ...
www.ncbi.nlm.nih.gov/pubmed/17948336

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Note added at 25 mins (2010-08-05 19:17:49 GMT)
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Elevated serum bilirubin levels are caused mainly by liver diseases, ... were selected to participate in an open-label, two-phase clinical trial. ... carriers had higher baseline serum UCB, T.BIL and D.BIL levels compared with subjects ...
www.ncbi.nlm.nih.gov/pubmed/17973861Clinical significance of serum bilirubin levels under ...
by AM Bonnand - 1999 - Cited by 50 - Related articles
We determined whether the normalization of serum bilirubin level (SBL) induced by ... SBL normalized with treatment and placebo patients who had normal baseline SBL. ... Publication Types: Clinical Trial; Randomized Controlled Trial ...
www.ncbi.nlm.nih.gov/pubmed/9862847

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Note added at 28 mins (2010-08-05 19:20:41 GMT)
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The importance of the serum creatinine level as a prognostic indicator for ... POSCH was a randomized, controlled clinical trial designed to assess whether ... For this analysis of the relationship between baseline serum creatinine and ...
findarticles.com/p/articles/mi_m0689/is.../ai_13928813/ - Cached - Similar

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Note added at 29 mins (2010-08-05 19:22:04 GMT)
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The "baseline value" is the value before the subject/patient takes the study drug.

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Note added at 31 mins (2010-08-05 19:23:36 GMT)
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First entry : I meant "follow-up visit"

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Note added at 37 mins (2010-08-05 19:29:43 GMT)
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I have worked for many years with clinical studies and with breast and other cancer studies, if this can help.