What is Tetrabromophenol blue urine

Certain dyes ( such as Bromophenol blue, Crystal violet, Naphthol Yellow S, Alkaline Fast Green, Sulforhodamine B, Coomassie blue, and several other dyes) bind to proteins. The color intensity, i.e., protein amount corresponding to cell number, can be used in certain conditions instead of optical cell counting. The protein-bound dye is released using a specific solvent (except for covalently binding dinitrofluorobenzene), with the light absorption of the resulting solution being measured photometrically.

Commercial brands measure pH in increments of 0.5 or 1 pH units between pH 5 and 9. In order to differentiate pH in this wide range, it is common to use a double indicator system comprising methyl red and bromothymol blue. Methyl red produces a color change from red to yellow in pH 4 to 6, and the bromothymol blue changes from yellow to blue between pH 6 and 9. In the range 5 to 9, the strips show colors that change from orange at pH 5, passing through yellow and green to dark blue at pH 9.

Urinalysis dipsticks embedded with pH indicator dyes, such as tetrabromphenol blue, are widely used for screening proteinuria and renal pathology. Anionic albumin selectively extracts bound hydrogen ions to elicit a color change from yellow to blue. This method is based on the color change of indicators such as bromophenol blue, which is buffered to pH 3.0 with citrate and changes from yellow to blue when bound to albumin. This method offers rapid, inexpensive, semi-quantitative detection of urine proteins. However, package inserts and published studies caution that alkalinity, specific gravity, and dyes/detergents interfere with tetrabromphenol blue protein detection[1-2].

References

[1] Jason L. Robinson, Isolde Seiden-Long, Allison A. Venner . “Urine protein detection by dipstick: No interference from alkalinity or specific gravity.” Clinical biochemistry 71 (2019): Pages 77-80.

[2] Yi-Ju Chou. “Albuminuria Is Affected by Urinary Tract Infection: A Comparison between Biochemical Quantitative Method and Automatic Urine Chemistry Analyzer UC-3500.” Diagnostics 13 21 (2023).

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