Given normal iron studies and a peripheral smear showing teardrop cells, schistocytes, anisocytosis, macrocytosis, polychromasia, ovalocytes, and burr cells, what is the most likely diagnosis and what initial work‑up should be performed?

Myelodysplastic Syndrome (MDS) is the Most Likely Diagnosis—Proceed Immediately with Bone Marrow Evaluation

Given the combination of macrocytosis (3+), marked anisocytosis (3+), teardrop cells, and normal iron studies, you must perform bone marrow aspiration with biopsy, cytogenetics, and iron staining to evaluate for myelodysplastic syndrome (MDS).

Diagnostic Reasoning

The peripheral smear findings are highly suggestive of a primary bone marrow disorder rather than a nutritional or hemolytic process:

Key Smear Features Pointing to MDS

• Macrocytosis (3+) with anisocytosis (3+): This degree of size variation with predominant macrocytosis, combined with normal iron studies, strongly suggests dysplastic erythropoiesis rather than iron deficiency or hemolysis 1

• Teardrop cells (dacrocytes): These indicate marrow infiltration, fibrosis, or ineffective erythropoiesis—all consistent with MDS or myelofibrosis 2

• Schistocytes (1+): While typically associated with microangiopathic hemolytic anemia, schistocytes can appear in erythroleukemia and other myelodysplastic conditions. Research demonstrates that up to half of erythroleukemia patients may lack peripheral blasts but show microangiopathic changes 3. However, at 1%, this is below the 1% threshold typically diagnostic for thrombotic microangiopathy 4

• Polychromasia (2+): Suggests increased reticulocyte response, which you must quantify with a reticulocyte count/index to determine if this represents appropriate marrow response or ineffective erythropoiesis 1

Critical Distinction from Other Causes

The normal iron panel excludes iron deficiency anemia, which would be the primary consideration for microcytic disease 1. The macrocytosis with this degree of morphologic abnormality makes megaloblastic anemia (B12/folate deficiency) less likely, though these must still be checked 1.

Mandatory Initial Work-Up

Perform these tests immediately 2, 5, 2:

Blood Tests (Priority Order)

1. Reticulocyte count with reticulocyte index calculation - Distinguishes production vs. destruction/loss 1
2. Vitamin B12 and folate levels - Exclude megaloblastic causes 1, 5, 2
3. LDH, indirect bilirubin, haptoglobin - Assess for hemolysis 6, 2
4. Peripheral blood blast count - MDS diagnosis requires <20% blasts (≥20% = AML) 2, 7
5. Serum erythropoietin level - Prognostic and guides future treatment decisions 5, 8

Bone Marrow Evaluation (Mandatory) 2

All three components are required for MDS diagnosis:

1. Bone marrow aspirate with:

   • Morphologic evaluation of dysplasia in all three lineages (erythroid, myeloid, megakaryocytic)
   • Blast enumeration (count ≥500 cells including ≥100 erythroblasts, ≥30 megakaryocytes)
   • Iron staining (Perls stain) to identify ring sideroblasts (≥15% defines specific MDS subtype) 2

2. Bone marrow biopsy:

   • Assess cellularity (MDS typically hypercellular, occasionally hypoplastic)
   • Evaluate for fibrosis (may indicate myelofibrosis or fibrotic MDS variant)
   • Assess megakaryocyte morphology and topography 2, 9

3. Cytogenetic analysis (conventional karyotyping):

   • Detects clonal chromosomal abnormalities in >80% of MDS cases
   • Highest prognostic value of all parameters in risk stratification
   • Specific abnormalities (del(5q), -7/del(7q), complex karyotype) provide diagnostic and prognostic information 2, 9

Additional Recommended Tests 5, 2

• Flow cytometry immunophenotyping - Detects abnormal immunophenotypes in erythroid, myeloid, and megakaryocytic compartments
• FISH panel if conventional cytogenetics fail
• Molecular testing for recurrent mutations (SF3B1, TP53, ASXL1, etc.) - Increasingly important for diagnosis and prognosis 9
• PNH clone testing by flow cytometry 5, 2

Critical Diagnostic Pitfalls to Avoid

Do Not Delay Bone Marrow Evaluation

If dysplasia is present in ≥10% of cells in any lineage, or if unexplained cytopenia persists, bone marrow examination is mandatory 2. Waiting for "more obvious" findings delays diagnosis and appropriate risk stratification.

Recognize That MDS Can Mimic Other Conditions

• The presence of schistocytes may mislead toward thrombotic microangiopathy diagnosis, but the macrocytosis, teardrop cells, and normal platelets (presumably) argue against TTP/HUS 3, 4
• Macrocytosis with normal B12/folate still requires bone marrow evaluation—non-megaloblastic macrocytic anemia includes MDS, medications (hydroxyurea, azathioprine), and alcoholism 1, 6, 1

Understand That Normal Cytogenetics Do Not Exclude MDS

20-70% of MDS patients have normal karyotypes but harbor submicroscopic alterations, point mutations, or epigenetic changes 2, 9. Morphologic dysplasia remains the diagnostic cornerstone.

Observation Period Only for Minimal Findings

If only unilineage dysplasia exists, no blast increase, ring sideroblasts <15%, and normal cytogenetics, a 6-month observation with repeat bone marrow may be appropriate 2. However, your patient's marked morphologic abnormalities warrant immediate comprehensive evaluation, not observation.

Why This Matters for Morbidity and Mortality

Early MDS diagnosis is critical because:

• Risk stratification (IPSS-R, MIPSS70+) determines prognosis and guides treatment intensity 9, 8
• Allogeneic stem cell transplantation—the only curative option—is most effective when performed before disease progression or transformation to AML 5, 9
• Specific subtypes (e.g., del(5q) MDS) have targeted therapies (lenalidomide) with high response rates 8
• Transformation to AML occurs in 40-50% of higher-risk MDS, with worse outcomes than de novo AML 5