What is the primary limitation of the biuret reagent?

The primary limitation of the biuret reagent is that it is not sensitive enough for low protein levels. The biuret reaction is designed to detect peptide bonds, which are abundant in proteins. However, at lower concentrations of protein, the reagents may not produce a color change that is discernible above the baseline noise of the assay. This lack of sensitivity means that biuret reagent is not ideal for quantifying proteins at low levels, thereby limiting its effectiveness in clinical settings where monitoring low protein concentrations may be critical, such as in certain disease states or nutritional assessments.

The other options address limitations that, while they may be relevant, do not encapsulate the primary restriction inherent to biuret reagent usage in routine testing. For instance, sensitivity to hemolysis refers to false elevations in protein levels due to hemoglobin interference, but this does not fundamentally limit the assay’s use for measuring normal protein levels. The precision required to only measure albumin is not accurate since the biuret reagent can detect a range of proteins, not just albumin. The concern about a long incubation period is generally not characteristic of biuret assays, which typically have rapid reaction times, making this a lesser limitation.