What is Poikilocytosis?
Poikilocytosis refers to the presence of abnormally shaped red blood cells (RBCs) in the peripheral blood, representing a deviation from the normal biconcave disc morphology. This finding indicates underlying pathology affecting RBC production, structure, or destruction 1.
Clinical Significance
Poikilocytosis is not a diagnosis itself but rather a laboratory finding that signals various underlying conditions:
- Iron deficiency anemia causes shape changes from normal biconcave disks to rigid microcytic microspheres, particularly when combined with polycythemia in cyanotic heart disease 2
- Myelodysplastic syndromes (MDS) present with dysplastic erythropoiesis and various poikilocyte forms, often accompanied by other dysplastic features like pseudo-Pelger-Huët cells 3
- Myelofibrosis and myeloproliferative disorders commonly show teardrop cells (dacrocytes), a specific type of poikilocyte 3
- Vitamin B12 deficiency can cause marked poikilocytosis that mimics schistocytes, potentially leading to misdiagnosis as thrombotic microangiopathy 4
- Malignancy, particularly adenocarcinoma of the gastrointestinal tract with metastatic disease, shows poikilocytosis in 12% of cases and carries poor prognosis (50% mortality within one month) 5
Diagnostic Approach
Peripheral blood smear examination is essential for identifying poikilocytosis and characterizing the specific RBC shape abnormalities present 2, 1.
Key Morphological Patterns to Identify:
- Schistocytes (fragmented cells) suggest microangiopathic hemolytic anemia rather than marrow pathology 3
- Teardrop cells point toward myelofibrosis or marrow infiltration 3
- Acanthocytes and echinocytes (spiculated cells) may indicate membrane defects or metabolic abnormalities 6
- Macrocytic poikilocytes with hypersegmented neutrophils suggest megaloblastic anemia from B12 or folate deficiency 4
Critical Laboratory Evaluation:
- Complete blood count to assess for anemia, thrombocytopenia, and mean corpuscular volume 4, 6
- Reticulocyte count distinguishes hemolytic processes (elevated) from production defects (low); notably, B12 deficiency shows low reticulocytes despite hemolysis 4
- LDH and haptoglobin assess for hemolysis; LDH >2500 IU/L more commonly indicates B12 deficiency than thrombotic microangiopathy 4
- Iron studies and B12/folate levels to identify nutritional deficiencies 2, 4
When to Pursue Bone Marrow Examination:
Bone marrow aspiration and biopsy with reticulin staining is necessary when MDS, myelofibrosis, or other marrow pathology is suspected, particularly with concurrent cytopenias, dysplastic features, or unexplained poikilocytosis 3.
- Cytogenetic and molecular testing should accompany marrow examination, as chromosomal abnormalities occur in up to 80% of MDS patients 3
- Flow cytometry helps distinguish clonal from reactive causes 7
Common Pitfalls to Avoid:
- Do not confuse marked poikilocytosis from B12 deficiency with true schistocytes from thrombotic microangiopathy; check reticulocyte count (low in B12 deficiency) and B12 levels before initiating plasma exchange 4
- Do not overlook poikilocytosis in non-anemic patients with cancer, as it carries prognostic significance independent of hemoglobin level 5
- Ensure proper anticoagulant volume when collecting samples from polycythemic patients, as excess anticoagulant can falsely suggest coagulation abnormalities 2
- In neonates with hemolytic anemia and poikilocytosis, consider infantile pyknocytosis, which resolves spontaneously and may respond to erythropoietin rather than requiring transfusion 8