Table 3. World Health Organization (WHO) Peripheral Blood and Bone Marrow Findings for Myelodysplastic Syndromes (MDS)
| | RCUD (including RA, RN and RT) | RARS | RCMD | RAEB-1 | RAEB-2 | MDS-U | del(5q) |
| Cytopenia(s) | Unicytopenia or bicytopeniaa | | + | + | + | + | |
| Anemia | | + | | | | | + |
| Platelets | | | | | | | Normal to increased |
| Marrow dysplasia | | | | UL or ML | UL or ML | | |
| erythroid | | + | | | | | |
| myeloid | ≥10% in 1 myeloid lineage | | ≥10% in ≥2 myeloid lineages | | | <10% in ≥1 myeloid lineageb | |
| megakaryocytic | | | | | | | Normal to increased with hypolobulated nuclei |
| Auer's rods (blood and/or bone marrow) | | | None | None | ±c | | None |
| Ringed sideroblasts | <15% of EP | ≥15% of EP | ± 15% | | | | |
| Peripheral blasts | Rare or none (<1%)d | None | Rare or none (<1%)d | <5%d | 5%–19% | (≤1%)d | Rare or none (<1%) |
| Bone marrow blasts | <5% | <5% | <5% | 5%–9%d | 10%–19% | <5% | <5% |
| Peripheral monocytes | | | <1 x 109/L | <1 x 109/L | <1 x 109/L | | |
| Cytogenetic abnormality | | | | | | | Isolated del(5q) |
| EP = erythroid precursors; MDS-U = myelodysplastic syndromes, unclassifiable; ML = multilineage; RA = refractory anemia; RAEB = refractory anemia with excess blasts; RARS = refractory anaemia with ring sideroblasts; RCMD = refractory cytopenia with multilineage dysplasia; RCUD = refractory cytopenia with unilineage dysplasia; RN = refractory neutropenia; RT = refractory thrombocytopenia; UL = unilineage. |
| aBicytopenia may occasionally be observed. Cases with pancytopenia should be classified as MDS-U. |
| bWhen accompanied by cytogenetic abnormality considered as presumptive evidence for a diagnosis of MDS. |
| cCases with Auer rods and <5% myeloblasts in the blood and <10% in the marrow should be classified as RAEB-2. |
| dIf the marrow myeloblast percentage is <5% but there are 2%–4% myeloblasts in the blood, the diagnostic classification is RAEB-1. Cases of RCUD and RCMD with 1% myeloblasts in the blood should be classified as MDS-U. |
