Cerebrospinal fluid/serum ratio

Oral bioavailability exceeds 80% and is not food-dependent. In children, the mean cerebrospinal fluid plasma ratio of lamivudine was 0.2. Serum half-life is 2.5 hours, whereas the intracellular half-life of the triphosphorylated compound is 11-14 hours. Most of lamivudine is eliminated unchanged in the urine (Table 49-3). 

J. F. Caro, J. W. Kolaczyn.ski, M. R. Nyce, et al. Decreased cerebrospinal-fluid/serum leptin ratio in obesity A possible mechanism for leptin resistance. Lancet 348, 159(1996). 

Immunoglobulin G index The ratio of immunoglobulin G to protein in the serum or cerebrospinal fluid. 

Nephelometric methods in general are more sensitive than turbidimetric assays and have an average lower limit of detection of 0.1 to 10 mg/L for a serum protein. Lower detection limits are obtained in fluids, such as cerebrospinal fluid and urine, because of their lower lipid and protein concentrations, which results in a better signal-to-noise ratio. In addition, for low molecular weight proteins (e.g., myoglobin, MW 17,800), assay detection Emits can be lowered using a latex-enhanced procedure based on antibody-coated latex beads. ... 

Also, hCG is useful in identifying patients with trophoblastic tumors and, together with AFP, in detecting non-seminomatous testicular tumors. Levels of hCG correlate with the tumor volume and disease prognosis. The presence of hCG in seminoma may indicate the presence of choriocarcinoma. Because hCG does not cross the blood-brain barrier, the normal cerebrospinal fluid-to-serum ratio is 1 60. Higher levels in cerebrospinal fluid may indicate metastases to the brain. Furthermore, the response to therapy for patients with central nervous system metastasis may be indicated by monitoring the hCG level. 

Memantine s elimination half-life is approximately 60-80 hr it is excreted mainly unchanged through the kidneys and undergoes limited metabolism in the liver. The concentrations of memantine in the cerebrospinal fluid (CSF) were shown to eorretate well with its serum levels, with a CSF serum ratio of 0..52 (Komhuber and Quack, 1995). Memantine has also been shown to have minimal inhibitory elfea on CYP450 enzymes (Periclou eial., 2004). 

Interest in the role of vitamin E in disease prevention has encouraged the search for reliable indices of vitamin E status. Most studies in human subjects make use of static biomarkers of status, usually a-tocopherol concentrations in plasma, serum, erythrocytes, lymphocytes, platelets, lipoproteins, adipose tissues, buccal mucosal cells, and LDL, and the a-tocopherol 7-toco-pherol ratio in serum or plasma. Other markers of vitamin E status include susceptibility of erythrocyte or plasma LDL to oxidation, breath hydrocarbon exhalation, and the concentration of a-tocopherol quinone in cerebrospinal fluid. There is no consensus as to the threshold concentration of plasma or sermn a-tocopherol at which a person can be defined as having inadequate tocopherol status, but values of <11.6, 11.6-16.2, and >16.2 pmol are normally regarded as indicating a deficient, low, and acceptable vitamin E status, respectively. It is recommended that... 

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