Low blood counts: immune mediated, idiopathic, or myelodysplasia

Traditionally, cytopenias are classified as deficiency mediated, immune mediated, BM failure induced, renal, or idiopathic, with the latter including the so-called idiopathic cytopenias of undetermined significance (ICUS). Clinical findings, symptoms, blood counts, BM findings, and other laboratory parameters are usually sufficient to reveal the type and cause of a marked cytopenia. However, in patients with chronic mild cytopenia, it may be a challenge for the physician to establish a correct diagnosis. In such patients, laboratory features and findings often reflect a diagnostic interface, so that criteria that are otherwise robust may hardly be applicable or are not helpful. Even if the BM is examined, the diagnosis often remains uncertain in these patients. In addition, more than one potential cause of cytopenia may be present, especially in the elderly. A myelodysplastic syndrome (MDS) or another BM disorder, but also an overt autoimmune or other inflammatory disease, may develop during follow-up in these patients. A key problem is that in an early phase of MDS, most laboratory and clinical signs are "nonspecific." One of the very few reliable peripheral blood parameters distinguishing between an early or "pre-phase" of MDS and most other causes of a mild cytopenia are the numbers of circulating colony-forming progenitor cells. In addition, flow cytometric and molecular investigations may sometimes assist in the delineation between clonal and reactive conditions underlying mild cytopenias. This review provides an overview of diagnostic approaches and algorithms for patients with mild unexplained cytopenia(s).