An acid direct cotton dye, it is absorbed by amyloid and induces green fluorescence to amyloid in polarized light; used as a laboratory aid in the diagnosis of amyloidosis, as a histologic stain, and as an indicator (pH 3.0, blue-violet, to pH 5.0, red) in testing for free hydrochloric acid in gastric contents. See Bennhold C. stain.
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Congo red .käŋ-(.)gō-'red n an azo dye C32H22N6Na2O6S2 that is red in alkaline and blue in acid solution and that is used in a number of diagnostic tests and esp. for the detection of amyloidosis since the injected dye tends to be retained by abnormal amyloid deposits
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a dark-red or reddish-brown pigment that becomes blue in acidic conditions. It is used as a histological stain. amyloidosis is indicated if over 60% of the dye disappears from the blood within one hour of injection.
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an odorless, dark red or reddish brown powder that decomposes on exposure to acid fumes; used as a biological stain, as an indicator with a pH range of 3.0 (blue-violet) to 5.2 (red), and as a diagnostic aid in amyloidosis See also under tests.Medical dictionary. 2011.