Urinalysis by means of Test Strips
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Test strip - general information

Test strips are used to analyze urine pH and specific gravity, and to demonstrate the presence of glucose, bilirubin, ketones (acetoacetic acid), blood, protein, urobilinogen, nitrites, leukocytes and ascorbic acid in urine (depending on the type of test strip used). Test strips are used for rapid and reliable demonstration and semiquantitative determination of particular analytes in urine by quite a simple procedure.
While working in a medical biochemistry laboratory in Vienna in 1920s, Fritz Feigl began to think about a more rapid testing for certain urine compounds by filter paper impregnation with particular reagents. Some 20 years elapsed from the idea to its implementation. In 1935, a report on rapid urinalysis by test strips appeared in the journal of the Leipzig Academy of Sciences. However, Feigl's invention found routine application years later, when industry manufacture of strips for rapid urine testing started. First strips were intended for a single parameter, e.g. glucose, albumins, ketones, etc. Then, Ames started the manufacture of test strips for simultaneous determination of a number of analytes, e.g. Hema-combistix for protein, glucose, pH and acetone. The shortcoming of these first test strips was their instability due to the reagent susceptibility to the effect of moisture (with filter paper as a medium). Later on, filter paper as a carrier was substituted by inert plastic strips with reagent-impregnated paper slips (6x6 mm slips of filter paper) pasted on.
Currently used test strips are made of plastic foil with reagent paper (impregnated reagents) at particular areas. A special layer to absorb excess fluid is placed underneath the reagent paper. A thin nylon mesh is stretched over the absorbent layer and reagent paper, fixing them to the foil and at the same time protecting them from any undesirable contact and contamination.

The strip allows the reagent paper (6x6 mm) to be uniformly perfused with urine while the reaction is proceeding steadily, together with removal of excess urine. The principles of reagent reactions in dry state for testing particular analytes in urine are identical to those performed in the test tube. A specific chemical reaction for determination of an analyte concentration is combined with an indicator or conjugated reagent to produce a color of varying intensity proportional to the tested analyte concentration.
The first test strips were manufactured in 1950 for diagnostic purpose, i.e. for the detection and follow-up of diabetes mellitus. These test strips contained reagents for demonstration of glucose in urine (Clinistix, Ames; S-Glucotest, Boehringer-Mannheim). Reagents for other tests were then gradually added onto the test strip. At present, 11 different urine parameters can be qualitatively or semiquantitatively determined by manual evaluation or automatically:
1. pH
2. glucose
3. protein
4. nitrites
5. urobilinogen
6. ketones
7. bilirubin
8. blood
9. leukocytes
10. specific gravity
11. ascorbic acid

Test strips have been continuously developed, e.g. new reagents to prevent interferences have been added to the layers with basic reagents (for instance, an iodate-impregnated layer oxidizing ascorbic acid in urine, thus preventing the potentially interfering effect, is being added onto the test strip for determination of blood in urine).
Test strips allow rapid and reliable demonstration and semiquantitative determination of particular analytes in urine. The use of test strips has a number of advantages:
• simple use,
• constant reagent composition,
• specificity for particular parameters, and
• long-term stability.

Disadvantages of the use of test strips include:
• inadequate sensitivity for some analytes (e.g. albumin),
• susceptibility to interferences, and
• semiquantitative results.

The test strip pack and vial are labeled with the type of analyte determined at each individual test strip area. Test strip areas are ready for use immediately upon being taken out from the vial. Test strips can be read manually, without any additional laboratory equipment, or on automated urine test strip readers of a number of manufacturers (e.g. Clinitec, Miditron, Rapimat II, etc.).
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