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The urine test strip test for blood is based on hemoglobin's pseudo peroxidase activity in catalysing a reaction between hydrogen peroxide and the chromogen tetramethylbenzidine in order to produce a dark blue oxidation product. [6] [13] the resultant colour can vary between green and dark blue depending on the amount of hemoglobin. [13]
It is advised to check the references for photos of reaction results. [1] Reagent testers might show the colour of the desired substance while not showing a different colour for a more dangerous additive. [2]
The test uses disks impregnated with a reagent such as N,N,N′,N′-tetramethyl-p-phenylenediamine, TMPD (or N,N-dimethyl-p-phenylenediamine, DMPD, which is also a redox indicator). The reagent is a dark-blue to maroon color when oxidized, and colorless when reduced.
The presence of nitrites, which causes a pink color on the reagent strip pad, therefore acts as an indicator of urinary tract infection. [51] The nitrite test is quite specific, meaning that someone is likely to have a UTI if it is positive, but it is not sensitive; a negative result does not reliably indicate that the subject does not have a UTI.
This test involves putting a drop of fluid obtained from the vagina onto paper strips containing nitrazine dye. The strips change color depending on the pH of the fluid. The strips will turn blue if the pH is greater than 6.0. A blue strip means it's more likely the membranes have ruptured. This test, however, can produce false positives.
Paper form: It is a strip of coloured paper which changes colour to red if the solution is acidic and to blue, if the solution is basic. The strip can be placed directly onto a surface of a wet substance or a few drops of the solution can be dropped onto the universal indicator using dropping equipment.
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