Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1229 page)

   Klinefelter syndrome levels lower than in normal male individual but higher than in normal female and orchiectomized male

   Estrogen therapy

   Total (but not free) testosterone decreased due to decreased SHBG (e.g., cirrhosis, chronic renal disease)

   Limitations

   Due to the availability of many different forms of testosterone assays, as well as the confusion in the literature regarding their clinical relevance, there is a lack of consistency for its measurement in routine clinical situations. The earliest approaches to the measurement of free testosterone were equilibrium dialyses and ultrafiltration. These assays were very cumbersome for routine use.

   Indirect measurement of free testosterone using isotope-labeled testosterone was one of the earlier methods proposed and widely used. The endocrine society recently reported a review of the evidence that the analog-based free testosterone immunoassays should be avoided because of the problems with accuracy and sensitivity. Free testosterone measurements by calculation using algorithms based on the law of mass action, which requires total testosterone, SHBG, and albumin concentrations, have excellent correlations with physical separation measures.

   Testosterone exhibits significant circadian variations in young men, and early morning samples are recommended.

THEOPHYLLINE (1,3-DIMETHYLXANTHINE)
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   Definition

   A naturally occurring (tea) xanthine derivative with diuretic, cardiac stimulant, and smooth muscle relaxant properties. Other names: Theo-Dur, Uniphyl, Slo-bid, and Theolair.

   
Normal range:

   0–5 months: 6–12 μg/mL

   Greater than 6 months: 10–20 μg/mL

   Use