Screening tests disadvantage

Protein arrays may offer advantages over libraries. The array format provides a precise spatially oriented grid that allows side-by-side comparison of assay results for all of the proteins on the array. The spatial arrangement also permits immediate identification of a clone that tests positive in an assay based on its location on the array. Therefore, less effort is required to identify the protein responsible for an interaction than with a library screen. A disadvantage of a protein array, however, is that fewer proteins can be efficiently arrayed and screened ( 104) versus a library ( 109). Therefore, the number of elements that can be effectively arrayed and assayed currently limits protein arrays. 

Physiologic Function Testing, An example of this application is the assay of thyroid hormone levels in (lie blood winch, in turn, can aid in the assessment of thyroid function. The radioactive iodine uptake test, which involves the administration of a dose of l31l (iodine-131) to the patient, is also a valuable procedure in assessing thyroid function. At present, the technique is best reserved for problem cases rather than used as a primary screening test. The main disadvantage of this test is the effect of the dietary intake of iodine, which reacts in various ways in different individuals. 

These simple psychometric screening tests do, however, have certain disadvantages, which have to be considered when results are being assessed, (s. tab. 10.5)... 

More recently, there has been much effort to replace animal tests with in vitro test models, such as isolated tissues and cell cultures (Hutak and Jacaruso 1996). These have some advantages in that they are less costly than in vivo tests, use relatively simple methodology and can be used to identify primary changes at the cellular level. The disadvantages are that they do not mimic the eye response, they cannot be used to evaluate insoluble materials (e.g., suspensions), and the various methods differ widely in their ability to predict irritancy potential. It is conceivable that in vitro methods could be used for primary screening tests, while more standard in vivo methods are used to verify the result. 

The main disadvantage of these screening tests is that the test conditions tend towards being isothermal (whereas the conditions in a reactor runaway are nearer adiabatic). This can mean that the tests are not always sufficiently sensitive, and that the measured onset temperature for thermal decomposition is a function of the sample heating rate. Also, the small sample size may lead to it being unrepresentative of plant materials, and evaporation losses can lead to errors unless sealed test cells are used. 

The test is primarily a screening tool relative to reactivity of substances and reaction mixtures and is highly useful for that purpose. The determined initiation temperature is approximate. The energy calculations based on temperature increase and heat capacities are semi-quantitative because of the quasi-adiabatic mode of the system operation. The method of insulating the test cell results in moderate reproducibility of temperature rise and related pressure rise. Another disadvantage is the relatively small sample quantity with respect to full scale quantities thus, there could be a problem in that the sample may not be truly representative. 

---