Table 4. Comparison of Criteria Defining Idiopathic Cytopenia of Unknown Significance (ICUS) and Idiopathic Dysplasia of Unknown Significance (IDUS).

Diagnosis/Condition	Defining Criteria	Additional Features
MDS, myelodysplastic syndromes; EPO, erythropoietin; FISH, fluorescence in situ hybridization; BM, bone marrow. *constant: at least 6 months: marked: hemoglobin <10 g/dL, neutrophils <1,000/μL blood, platelets <100,000/μL; **diagnostic dysplasia: ≥10% of cells in one or more major hematopoietic lineages; karyotypes typically found in MDS; it is important to note that the diagnosis IDUS should only be established when clear signs of dysplasia in at least two hematopoietic lineages are detectable. ***if one or more co-criteria are found in suspected MDS, the condition should be termed “highly suspicious for MDS”.
ICUS	Constant marked cytopenia* No MDS detected by criteria No dysplasia/karyotype** No MDS-Co-Criteria*** No other disease as a primary reason for cytopenia found	elderly patients EPO levels low FISH may reveal a small MDS-clone in the bone marrow
IDUS	No constant marked cytopenia* No MDS found by criteria Dysplasia and/or karyotype** No other disease as reason for Dysplasia/karyotype detected	often young patients usually detected in a routine blood test (e.g. ‘Pelger forms’ or macrocytosis)