Qualitative Screening Tests

A useful qualitative screening test for salicylic acid is performed by adding a few drops of glacial acetic acid or 0.1N hydrochloric acid to 1 ml of urine, followed by 3 drops of 10% ferric chloride solution. A burgundy red color appears and persists if salicylic acid is present (color may turn reddish brown in the presence of phenothiazines). A serum salicylate level can be obtained in most laboratories. Commerically available test strips may be used with urine as well as serum or plasma to determine the presence of salicylic acid. These tests react only with salicylic acid and therefore do not work on stomach contents or pills, but any salicylate is hydrolyzed in the body to salicylic acid and would be present as such in blood or urine (15). 

Qualitative and quantitative analyses of -S-HIAA in urine were first described in 1955. Historically, two photometric methods for qualitative screening were used. The nitroso-naphthol-nitrous acid procedure was more specific and widely used than the dimethylaminobenzaldehyde (Ehrlich s aldehyde) procedure. These qualitative screening tests, however, are no longer recommended since they are insensitive and susceptible to interference. 

Qualitative screening tests in which urine is reacted directly with Ehrlich s reagent and assessed visually for the formation of the red chromogen (e.g., the Watson-Schwartz and Hoesch tests) are convenient but have been criticized for poor detection limits and interferences, even when solvent extraction has been used to separate the PBG-Ehrlich compound from the urobilinogen-Ehrfich complex. ... 

If a qualitative screening test is used, it is essential to include appropriate controls and confirm ail positive test results using a specific quantitative method. ... 

Methods for porphyrin fractionation are complex and time consuming and not available in every laboratory. For this reason, simple qualitative screening tests are often used to exclude the majority of specimens that do not require further investigation from the few that justify fractionation of the individual porphyrins. Screening tests in which extracts of urine or feces are examined visually for typical red-pink fluorescence of porphyrins lack sensitivity and should not be used. Methods based on spectrophoto-metric scanning of acidified urine or fecal extracts for the presence of the Soret band are recommended and yield semiquantitative information. Quantitative fluorometric methods are also available. ... 

Rosenthal, A. F., and Yaseen, A., Improved qualitative screening test for cystinuria and homocytinuria. Clin. Chim. Ada 26, 363-364 (1969). 

Although screening tests are evaluated qualitatively, as a rule, quantitative aspects of test statistics and probability theory have to be considered. In this respect, validation of qualitative analytical procedures has been included in international programs and concepts, see Trullols et al. [2004]. 

Differential Thermal Analysis (DTA) A sample and inert reference material are heated at a controlled rate in a single heating block. This test is basically qualitative and can be used for identifying exothermic reactions. Like the DSC, it is also a screening test. Reported temperatures are not reliable enough to be able to make quantitative conclusions. If an exothermic reaction is observed, it is advisable to conduct tests in the ARC. 

The test based on motility inhibition of the bacterium Spirillum volutants is a very simple and rapid test for the qualitative screening of wastewater samples or extracts [48]. The organisms are observed under the microscope immediately after the addition of the test solution. The maintenance of a bacterial culture is necessary as in the previous type of assay. 

Qualitative screening procedures were used to test toxins as sole carbon sources for growth of the cigarette beetle symbionts. 

The types of test to be performed depend on the clinical situation. If the patient has an acute, severe disease and an acute porphyria is suspected, PBG should be assessed either qualitatively by a reliable screening test or quantitatively in a spot urine. Quantitative ALA can be added to uncover lead intoxication, which may be clinically undistinguishable from an acute porphyria. Furthermore, the extremely rare ALAD deficiency may show normal PBG. If increased values of PBG are present, urinary porphyrins can be determined to confirm the existence of porphyria. 

Enzyme immunoassay kits are now available for qualitative field testing or for laboratory screening and semiquantitative analysis of pesticides, herbicides, polychlorinated biphenyls (PCBs), mononuclear and polynuclear aromatic hydrocarbons, pentachlorophenol, nitroorganics, and many other compounds in aqueous and soil samples. Certain analytes may be quantitatively determined as well, with a degree of accuracy comparable to gas chromatography or high performance liquid chromatography determination. The method is rapid and inexpensive. 

Unconscious patients are usually catheterised and, in this case, the sample may be contaminated with the catheter lubricant which frequently contains lignocaine as a local anaesthetic. Urine is ideal for qualitative screening as it is available in large volumes, and usually contains higher concentrations of drugs or poisons than blood. The presence of drug metabolites can be used to assist identification if chromatographic techniques which can separate them are used. A 50-ml sample is sufficient for a comprehensive series of tests, and no preservative should be added. 

If increased urinary PEG was found by a qualitative and/or semiquantitative screening test, then this finding... 

A qualitative colorimetric test based on the inhibition of AChE can screen the presence of OPs and CMs. The thioesters of OPs have to be activated by a dilute bromine solution. Cummercial test kits are available for the coiori-metrie lest from Strategic Diagnostic. 

GC and HPLC methods, not fully investigated, may be used for qualitative monitoring. It may be noted that exposure to certain chemicals, such as parathion, may also produce p-nitrophenol as a urinary metabolite. A screening test for nitrobenzene exposure may be performed by monitoring methe-moglobin in the blood. 

Two bacteria isolated from the ceca of all test animals were Escherichia coli and Enterobacter sp. No pathogenic bacteria (e.g. Salmonella typhimurium) were identified. The absence of this latter organism helped rule out enterotoxemia as a cause of death in one animal and impaired growth in a second animal consuming 20% chltosan in their diets. Chltosan and chitin did not appear to change the intestinal flora population either quantitatively or qualitatively. Screening of anaerobic bacteria was not performed. 

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