Injection time, competitive binding

The utilization of lAC in analytical methods has received increasing retention in recent years [23,24], Of particular interest is the use of immobilized antibody columns in performing immunoassays, a technique known as a chromatographic immunoassay or flow-injection immunoassay. This approach has already been reported in a number of formats such as those involving simple analyte adsorption/desorption, sandwich immunoassays, competitive binding immunoassays, and multianalyte methods (see Figure 13,9) [23,24,73,74], Typical advantages of these methods include decreased analysis times and improved precision versus manual immunoassays. 

Artefactual increases of as much as 50% in total thyroxine, estimated by a competitive protein-binding assay, and of as much as 30% in triiodothyronine resin uptake are probably due to rapid and continuing lipolytic hydrolysis of triglycerides after blood has been drawn (126). Thyroid function tests should therefore always be performed on blood samples taken before (or a sufficient time after) heparin treatment (127). An increase in serum-free thyroxine concentrations has also been reported after low molecular weight heparin, by up to 171% in specimens taken 2-6 hours after injection. When specimens were obtained 10 hours after injection, the effects were smaller, but with concentrations still up to 40% above normal the results can still cause errors of interpretation (128). 

Physicians treat methanol or ethylene glycol poisoning with intravenous injections of ethanol before substantial oxidation has occurred. LADH binds more tightly to ethanol than to methanol or ethylene glycol, and the rate of oxidation of ethanol is about six times faster than that of ethylene glycol. The ethanol concentration can be kept higher because it is directly injected. As a result, neither methanol nor ethylene glycol is competitively oxidized to toxic products, and the kidneys can slowly excrete them. 

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