The Qubit RNA XR (Extended Range) Assay Kit, designed for use with the Qubit 4 and Qubit Flex fluorometers, provides an accurate and selective method for the quantitation of high-abundance RNA samples. The assay is highly selective for RNA and does not quantitate DNA, protein, or free nucleotides. Common contaminants, such as salts, free nucleotides, solvents, detergents, and protein, are well-tolerated in the assay. The assay kit is designed to be accurate for initial RNA sample concentrations of 10 to 10,000 ng/μL depending on sample volume, providing a linear detection range of 200−10,000 ng. The kit provides concentrated assay reagent, dilution buffer, and pre-diluted RNA standards. Simply dilute the reagent using the buffer provided, add the sample (any volume between 1 µL and 20 µL is acceptable), and read the concentration using a Qubit 4 or Qubit Flex fluorometer.