Haemolysis index for the screening of intravascular haemolysis: a novel diagnostic opportunity?

The diagnostic approach to patients with intravascular haemolysis remains challenging, since no first-line laboratory test seems to be entirely suitable for the screening of this condition. Recent evidence shows that an enhanced cell-free haemoglobin (fHb) concentration in serum or plasma is a reliable marker of red blood cell injury, and may also predict clinical outcomes in patients with different forms of haemolytic anaemias. However, the routine use of the haemiglobincyanide assay, the current reference method for measuring fHb, seems unsuitable for a timely diagnosis of intravascular haemolysis, for many safety and practical reasons. The spectrophotometric assessment of fHb by means of the so-called haemolysis-index (H-index) has now become available in most clinical chemistry analysers. This measure allows an accurate, rapid and inexpensive assessment of fHb in a large number of serum or plasma samples, and its use has already proven to be useful for identifying some forms of haemolytic anaemias. Therefore, the aim of this article is to provide an update and a personal opinion about the potential clinical use of the H-index for screening patients with suspected intravascular haemolysis.