Abstract: The present invention relates to labelling agents comprising non-proteinaceous boronic acid conjugates having absorption maxima at not less than 600 nm, said label being provided by e.g., an azine, triphenylmethane, cyanine or phthalocyanine dye. The labelling agents are useful in the estimation and quantification of cisdiols such as glycosylated haemoglobin, by virtue of the substantially total absence of overlap with the absorption spectrum of haemoglobin. Oxazine and thiazine dyes exhibiting similar absorption characteristics and containing other activated moieties are similarly useful labelling agents, especially in the presence of haemoglobin.

Abstract: A method of assessing glycosylated haemoglobin in a sample, wherein the method comprises the steps of (a) contacting the sample with signal-forming molecules comprising a conjugate of one or more dihydroxyboryl residues or salts thereof, linked to a signal-forming label; (b) separating by selective precipitation from a homogenous solution, glycosylated and non-glycosylated haemoglobin and any molecules bound thereto, from the reaction mixture of step (a) above; and (c) assessing signal-forming molecules selected from the group consisting of signal-forming molecules which have bound to the separated haemoglobin, and non-haemoglobin bound signal-forming molecules. Steps (a) and (b) may be performed simultaneously or sequentially. The sample may optionally be haemolyzed to liberate any cell bound haemoglobin. The invention also comprises an analytical test kit for use in accordance with the method of the invention.