Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (666 page)

   A negative immunoassay result in the setting of a strongly suggestive history does not exclude allergy. In this situation, a skin prick test should be considered (if not contraindicated).

   False-positive results of allergen-specific IgE can theoretically occur in patients with extremely elevated total IgE levels.

   Tests used largely in research settings include immunoblotting, basophil histamine or leukotriene release tests, basophil activation, and levels of eosinophil mediators, etc., are not standardized, and are generally not superior to skin testing, and cannot be recommended for routine clinical use.

   Allergen-specific IgG and IgG4 tests, which are believed to correlate with normal immunologic responses to foreign substances, are not useful in the diagnosis of IgE-mediated allergy, with the exception of venom allergy. Unreliable testing methods include provocation/neutralization tests, kinesiology, cytotoxic tests, and electrodermal testing.

   In food allergy, circulating IgE antibodies may remain undetectable despite a convincing clinical history because these antibodies may be directed toward allergens that are revealed or altered during industrial processing, cooking, or digestion and therefore do not exist in the original food for which the patient is tested.

   Identical results for different allergens may not be associated with clinically equivalent manifestations, due to differences in patient sensitivities.

ALBUMIN, SERUM

   Definition

   Albumin is the most important protein and constitutes 55–65% of total plasma protein. Approximately 300–500 g of albumin is distributed in the body fluids, and the average adult liver synthesizes approximately 15 g/day. Albumin’s half-life is approximately 20 days, with 4% of the total albumin pool being degraded daily. The serum albumin concentration reflects the rate of synthesis, the degradation, and the volume of distribution. Albumin synthesis is regulated by a variety of influences, including nutritional status, serum oncotic pressure, cytokines, and hormones.

   
Normal range:

   0–4 months: 2.0–4.5 g/dL

   4 months−16 years: 3.2–5.2 g/dL

   >16 years: 3.5–4.8 g/dL