Continuing Education Activity

Poikilocytosis is a hematologic abnormality characterized by significant variation in red blood cell shape observed on peripheral blood smear and serves as an important indicator of underlying systemic or hematologic disease. Abnormal erythrocyte morphologies may include elongated, teardrop-shaped, crescent-shaped, flattened, or spiculated cells, reflecting disruptions in hemoglobin synthesis, membrane structure, or bone marrow function. Poikilocytosis is not a diagnosis but a morphologic finding associated with diverse conditions, including nutritional deficiencies, hemoglobinopathies, hemolytic anemias, bone marrow disorders, liver disease, and microangiopathic processes. Recognition of specific red blood cell forms provides valuable diagnostic clues and may signal severe or progressive disease requiring prompt evaluation.

This educational activity enhances clinician competence in recognizing and interpreting poikilocytosis within the clinical context. Participants learn to identify characteristic erythrocyte shapes, correlate smear findings with laboratory data and patient presentation, and determine appropriate diagnostic pathways. The course emphasizes timely evaluation of underlying etiologies and principles of etiology-directed management to reduce morbidity. Collaboration among clinicians, hematopathology specialists, laboratory professionals, and nursing staff strengthens diagnostic accuracy, facilitates an efficient workup, and supports coordinated care, ultimately improving patient outcomes by enabling earlier recognition and targeted intervention.

Objectives:

• Identify abnormal red blood cell morphologies on peripheral blood smear consistent with poikilocytosis.
• Interpret peripheral blood smear findings in conjunction with automated hematologic indices to enhance diagnostic accuracy.
• Apply evidence-based management strategies focused on treating the underlying etiology rather than the morphologic abnormality alone.
• Collaborate with interprofessional team members, including hematologists, pathologists, nurses, and pharmacists, to optimize patient care.

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Introduction

Poikilocytosis refers to the presence of abnormally shaped red blood cells (RBCs) in the peripheral blood. Under normal conditions, RBCs (erythrocytes) exhibit a biconcave disc shape, with central pallor, a morphology that supports flexibility and efficient oxygen transport. A typical RBC measures approximately 6.2 to 8.2 µm in diameter, with a maximal thickness of 2 to 2.5 µm at the periphery and 0.8 to 1 µm at the center.[1]

Poikilocytosis is generally defined as when abnormally shaped RBCs comprise 10% or more of the total erythrocyte population. Poikilocytes may appear flat, elongated, teardrop-shaped, or crescent-shaped, and may display point-like or thorn-like projections, among other morphological abnormalities. The presence and distribution of poikilocytes often provide a hematologic "fingerprint" that helps identify the underlying disease.

Etiology

Poikilocytosis results from internal cellular damage or external (environmental) trauma to RBCs. Broadly, its causes may be classified as inherited or acquired. Inherited forms arise from genetic abnormalities or mutations affecting erythrocyte structure or membrane stability. In contrast, acquired forms typically develop later in life due to systemic disease, nutritional deficiencies, or environmental exposures (see Table 1). Inherited causes of poikilocytosis include a range of genetic disorders that affect RBC membrane integrity, cytoskeletal proteins, or hemoglobin structure. These abnormalities lead to impaired erythrocyte deformability, reduced cellular stability, and increased susceptibility to hemolysis, resulting in characteristic morphologic changes on peripheral blood smear.

• Sickle cell anemia: Erythrocytes assume an abnormal crescent or elongated, spiculated shape known as sickle cells (drepanocytes) [2]
• Thalassemia: A genetic disorder characterized by defective hemoglobin synthesis, commonly demonstrates target cells (codocytes) (see Image. β-Thalassemia Minor)
• Hereditary spherocytosis: Marked by the presence of spherocytes (see Image. Hereditary Spherocytosis) [3]
• Pyruvate kinase deficiency: Associated with echinocytes (burr cells)
• Hereditary elliptocytosis: Characterized by elliptocytes [4]
• McLeod syndrome: A rare genetic condition, distinguished by the presence of acanthocytes

Acquired causes of poikilocytosis include systemic, nutritional, immune-mediated, toxic, and infectious conditions. These processes alter RBC morphology through mechanisms such as metabolic stress, membrane damage, oxidative injury, or mechanical fragmentation, often reflecting the severity and chronicity of the underlying disease.

• Iron deficiency anemia: A common nutritional anemia, associated with elliptocytes (see Image. Normal Versus Iron Deficiency Anemia)
• Megaloblastic anemia: Resulting from folate or vitamin B-12 deficiency, characteristically demonstrates dacrocytes (teardrop cells) and elliptocytes [5][6]
• Autoimmune hemolytic anemia: Commonly shows schistocytes and spherocytes

  • Schistocyte reporting has been standardized to improve diagnostic accuracy for thrombotic microangiopathy (TMA). The International Council for Standardization in Hematology (ICSH) recommends that >1% schistocytes on a peripheral blood smear is suspicious for TMA.[7]
• Chronic liver and kidney disease: Associated with echinocytes (burr cells)
• Alcohol-related liver disease: Characteristically demonstrates acanthocytes (spur cells)

  • Spur cell anemia is increasingly recognized as a marker of severe, advanced cirrhosis, with recent evidence suggesting spur cells exceeding 5% may be observed in a subset of patients and are associated with greater decompensation.[8]
• Myelofibrosis: Associated with dacrocytes
• Lead poisoning and other heavy metal exposure: Produces basophilic stippling, reflecting retained ribosomal RNA within the erythrocyte cytosol [9]
• Infectious etiologies: Includes Plasmodium and Babesia species; may demonstrate the causative organisms on peripheral smear, along with inclusions such as Howell-Jolly bodies (DNA remnants), Heinz bodies (denatured hemoglobin), and Pappenheimer bodies (iron deposits).[10]

Table

Table 1. Poikilocyte Morphology and Associated Clinical Conditions .

Epidemiology

Epidemiology varies according to the underlying cause of poikilocytosis. Sickle cell disease, an autosomal recessive hemoglobinopathy with multiple genetic variants, has the highest prevalence in Africa, followed by the Middle East and India, with lower prevalence reported in Europe.[11] Thalassemias are classified as α- or β-type. α-thalassemia is common in sub-Saharan Africa, the Mediterranean, tropical regions, and Southeast Asia, whereas β-thalassemia is commonly observed in the Mediterranean basin.[12] The geographic distribution of both forms reflects historical selective pressure from malaria, which has contributed to the persistence of thalassemia traits in endemic regions.

Hereditary spherocytosis predominantly affects individuals of European and North American ancestry, with an estimated prevalence ranging from approximately 1 in 2000 to 1 in 5000 individuals, particularly those of Northern European descent.[3][13] Pyruvate kinase deficiency is most frequently seen in Northern Europe and Japan.[14] Additionally, global migration has altered the geographic distribution of hemoglobinopathies, with increasing prevalence of sickle cell disease and thalassemia reported in regions where these conditions were previously uncommon.[15] 

Pathophysiology

Pathophysiology varies according to the underlying cause (see Table 2).[16] A key mechanism in poikilocytosis is impaired erythrocyte deformability. When RBCs lose membrane flexibility due to external or internal stressors, like oxidative injury, lipid membrane alterations, cytoskeletal defects, or mechanical stress, they struggle to pass through the splenic microcirculation.

The spleen functions as a physiologic "mechanical filter," detecting abnormalities in size, shape, and pliability. Cells that fail to deform appropriately are retained within the splenic cords and undergo macrophage-mediated clearance, a process that predominantly results in extravascular hemolysis.[17] In contrast, severe mechanical injury, microangiopathic processes, or toxin-mediated damage may result in intravascular hemolysis, characterized by RBC fragmentation and circulating schistocytes.

Table

Table 2. Red Blood Cell Poikilocytes: Mechanisms and Associated Conditions.

More recent studies have reported increased red blood cell morphologic abnormalities during acute SARS-CoV-2 infection, including higher frequencies of spiculated cells with echinocyte- or acanthocyte-like features, as well as other forms of poikilocytosis. These changes are thought to reflect inflammation-mediated membrane injury and metabolic stress associated with severe systemic illness.[39]

Histopathology

Histopathology plays a central role in evaluating poikilocytosis by allowing direct visualization of red blood cell morphologic abnormalities on peripheral blood smears. Careful assessment of erythrocyte shape, size, and membrane features provides critical diagnostic clues that reflect underlying defects in hemoglobin structure, membrane composition, or bone marrow function. When interpreted in conjunction with clinical findings and laboratory data, histopathologic evaluation helps narrow the differential diagnosis and guide further etiologic workup.

Drepanocytes

Drepanocytes (sickle cells) are characterized by intracellular polymerization of hemoglobin S, which forms rigid, elongated fiber bundles that distort the normal biconcave RBC into the characteristic crescent or sickle shape visible on a peripheral blood smear. This structural abnormality confers hypoxia sensitivity, such that the erythrocytes traverse relatively hypoxic regions of the microcirculation, reduced oxygenation promotes further HbS polymerization into rod-like structures, producing classic sickle forms and, less commonly, elongated cigar-shaped cells.[40][41]

Hemolysis of sickled erythrocytes amplifies disease severity by potentiating a systemic inflammatory state.[42][43] Intravascular hemolysis releases cell-free hemoglobin, leading to depletion of hemopexin, haptoglobin, and, most notably, nitric oxide.[44] Nitric oxide depletion results in platelet activation, upregulation of endothelial adhesion molecules, and vasoconstriction, collectively promoting vascular dysfunction, vaso-occlusion, and progressive end-organ injury.

Polymerized HbS damages RBC membranes, leading to dysregulated calcium and potassium flux. HbS polymers also precipitate along the inner surface of the erythrocyte membrane, promoting iron-mediated oxidative injury. These membrane and oxidative alterations increase erythrocyte rigidity and adhesiveness, facilitating abnormal attachment to the vascular endothelium and ultimately contributing to vascular occlusion.[42]

Spherocytes

Spherocytes are small, round erythrocytes that lack central pallor due to reduced membrane surface area and decreased deformability. Hereditary spherocytosis is autosomal dominant in approximately 75% of cases, with the remainder inherited in an autosomal recessive or de novo pattern.[45] Spherocytosis results from mutations in genes encoding RBC membrane or cytoskeletal proteins, including SPTA1, SPTB, ANK1, SLC4A1 (band 3), and EPB42 (protein 4.2), leading to increased membrane fragility, splenic sequestration, and extravascular hemolysis. Compensatory reticulocytosis may be present in cases of significant hemolysis.

Spherocytes are also seen in acquired conditions, most notably autoimmune hemolytic anemia, in which they are accompanied by a positive direct Coombs test and hyperchromic, densely hemoglobinized red cells.[16][45] Rarely, spherocytosis may be acquired in myelodysplastic syndromes, with a 2022 report implicating U2AF1 mutations as a mechanism for splicing factor-mediated membrane abnormalities.[46] Spherocytes may coexist with leukoerythroblastosis in marrow-infiltrative processes, a finding that typically reflects advanced disease and carries a poor prognosis. 

Condocytes

Codocytes (target cells) form when intracellular volume is disproportionately reduced relative to membrane surface area, resulting in redundant membrane that folds and remodels into a characteristic appearance consistent with a central hemoglobinized core surrounded by a zone of pallor and a peripheral ring of hemoglobin.[47] In liver disease, altered lipid metabolism, particularly reduced membrane cholesterol, decreases membrane tensile strength and promotes condocyte formation. In hemoglobinopathies, an uneven intracellular distribution of hemoglobin further distorts the surface area-to-volume ratio, producing target cells (see Image. β-Thalassemia Major). Condocytes may also occur artifactually in blood smears prepared under high-humidity conditions, typically comprising up to 5% of erythrocytes.

Schistocytes

Schistocytes are fragmented RBCs, produced by mechanical disruption within the circulation. Helmet cells represent a common subtype, formed when erythrocytes are sheared, leavin ga semicircular fragment with a straight edge and angular margins. Triangular cells are small, irregular remnants resulting from more extensive fragmentation.  Low-level schistocytosis may be physiologic, as schistocytes can be present in less than 1% of healthy adults and full-term neonates.[7] In newborns, pyknocytes—fragile, contracted erythrocytes—may be observed and can persist for up to 6 months in premature infants. 

Identification of schistocytes may be challenging when other abnormal cell types, such as echinocytes, acanthocytes, or crenated RBCs, obscure them. In such cases, supportive laboratory findings, including elevated lactate dehydrogenase, increased red cell distribution width, or polychromasia, may aid in diagnosis. The 2021 ICSH update recommends that schistocytes exceeding 1% on peripheral blood smear are suspicious for thrombotic microangiopathy and should be reported accordingly.[7]

Echinocytes and Acanthocytes

Echinocytes (burr cells) are typically reversible RBC dysmorphisms. They are characterized by preserved central pallor and multiple, small, uniformly distributed spicule-like projections.[25] Acanthocytes are spiculated erythrocytes with irregular projections of varying size, shape, and distribution (see Image. Acanthocytes).[28] Current models suggest that expansion of the outer RBC membrane layer produces the characteristic spicules, whereas expansion of the inner lipid bilayer results in stomatocytosis. In advanced stages, acanthocytes may undergo autophagic and autolysosomal degeneration.  

Dacrocyte and Elliptocytes

Teardrop cells (dacrocytes) are thought to arise through multifactorial processes with a shared underlying mechanism.[16][30] These erythrocytes are likely distorted or mechanically deformed as they traverse the bone marrow or splenic sinusoids, a hypothesis supported by reports of dacrocyte resolution following splenectomy. Elliptocytes arise from defects in the horizontal cytoskeletal network of RBCs, particularly involving impaired spectrin dimer interactions or disruption of spectrin-actin-protein 4.1 junctional complexes.[48][49] 

In hereditary elliptocytosis, pathogenic variants most commonly affect EPB4I (1p33-p32) erythrocyte membrane protein band 4.1, SPTA1 (1q21) α-spectrin erythrocyte, SPTB (14q24.1-q24.2) β-spectrin erythrocyte, and GYPC (2q14-q21) glycophorin C  or Gerbich blood groups. Hereditary pyropoikilocytosis represents a severe variant of elliptocytosis, characterized by marked membrane instability, hemolytic anemia, and jaundice in infancy.[49] Peripheral smears may resemble those seen in thermal burn injury, with microspherocytes and fragmented erythrocytes.

Degmacytes and Stomatocytes

Bite cells (degmacytes) arise from hemoglobin denaturation and precipitation within erythrocytes, forming Heinz bodies that are removed by splenic macrophages.[35][50] This pitting process excites the damaged membrane-hemoglobin complex, leaving the characteristic "bite" appearance on the peripheral smear. G6PD deficiency, an X-linked recessive disorder prevalent among African and Mediterranean populations, is a classic cause. Reduced enzymatic protection against oxidative stress leads to episodic hemolysis, particularly in older erythrocytes, while compensatory reticulocytosis may transiently normalize measured enzyme levels. Oxidative triggers include infections, fava bean ingestion, and medications such as phenazopyridine, nitrofurantoin, and sulfonamides.[36] 

Stomatocytes arise from dysregulated cation and water transport across the RBC membrane. Mutations in PIEZO1, which encodes a mechanosensitive transmembrane ion channel, disrupt calcium flux and impair cellular volume regulation.[38][51][52] Variability in red blood cell morphology reflects differences in PIEZO1 mutation type and expression, with dysfunction typically resulting in cellular dehydration and, less commonly, overhydration.[37] Hereditary stomatocytosis is now recognized as part of a broader PIEZO1-associated spectrum, particularly dehydrated hereditary stomatocytosis (hereditary xerocytosis). This evolving framework underscores the importance of interpreting stomatocytes in the context of clinical phenotype and genetic testing.[53]  

History and Physical

Poikilocytosis is a peripheral blood smear finding rather than a diagnosis itself; therefore, clinical evaluation should focus on identifying the underlying etiology. A thorough history should assess dietary intake (iron, folate, vitamin B12), gastrointestinal symptoms or malabsorption, alcohol use, medication exposures (particularly oxidative drugs), presence of prosthetic heart valves, recent infections, pregnancy or postpartum status (given thrombotic microangiopathy risk), transfusion history, and family history of hemolytic anemias or hemoglobinopathies. Because irregularly shaped erythrocytes may impair oxygen delivery, patients often present with nonspecific symptoms such as fatigue, pallor, dyspnea, palpitations, and generalized weakness. Poikilocytosis is typically defined by the presence of 10% or greater abnormally shaped RBCs on a peripheral smear. External stressors may exacerbate clinical manifestations by further impairing erythrocyte survival or function.

In sickle cell disease, exposure to cold, dehydration, or hypoxia may precipitate hemolytic, aplastic, or sequestration crises, acute chest syndrome, vaso-occlusive episodes, and eventual autosplenectomy. In HIV/AIDS, poikilocytosis has been reported in over half of patients, with anisocytosis observed in more than one-quarter.[54] Associated findings may include microcytosis, giant cells, target cells, nucleated reticulocytes, and polychromasia, reflecting disordered erythropoiesis; the extent to which highly active antiretroviral therapy contributes to these abnormalities remains unclear.

SARS-CoV-2 infection is associated with a broad spectrum of cytopathic hematologic findings, including fragmented neutrophils, macrothrombocytes, circulating erythroblasts, and diverse erythrocyte morphologic abnormalities.[55] These changes are thought to result from heightened inflammatory cytokine activity and thromboembolic disease, producing findings such as anisocytosis, spherocytes, polychromasia, stomatocytes, leukoerythroblastosis, knizocytes, and so-called “mushroom cells.” Knizocytes are centrally pinched, dumbbell-shaped erythrocytes, whereas mushroom (pincer) cells are pinched at one pole and represent a distinct morphology. β-thalassemia exemplifies the diversity of poikilocytosis, often demonstrating multiple abnormal erythrocyte forms simultaneously.[56] This morphologic heterogeneity reflects underlying pathophysiologic processes, including ineffective erythropoiesis, chronic hemolysis, iron overload with altered hepcidin regulation, persistent inflammatory signaling, and chronic tissue hypoxia.

Physical examination may reveal pallor and tachycardia, with jaundice and scleral icterus suggesting ongoing hemolysis. Splenomegaly raises concern for hereditary hemolytic disorders or hypersplenism. In contrast, hepatomegaly, ascites, or other stigmata of chronic liver disease may support spur cell anemia or target cell formation secondary to hepatic dysfunction. When poikilocytosis includes schistocytes, clinicians should urgently evaluate for thrombotic microangiopathy, including thrombotic thrombocytopenic purpura and hemolytic uremic syndrome, particularly in the presence of anemia with thrombocytopenia, neurologic manifestations, renal impairment, or hypertension.

Evaluation

Evaluation of poikilocytosis requires a systematic approach beginning with peripheral blood smear examination, followed by targeted testing based on the specific red blood cell morphology observed and clinical context.[57] The initial assessment should include a complete blood count with differential and reticulocyte count, a comprehensive metabolic panel, and careful microscopic examination of Giemsa-stained thick and thin peripheral blood films to identify the specific types of poikilocytes present (sickle cells, spherocytes, elliptocytes, target cells, schistocytes, or other abnormal forms). Additional first-line hemolysis markers include lactate dehydrogenase, fractionated bilirubin, and haptoglobin levels to assess for ongoing red blood cell destruction.

Once a poikilocytosis pattern is recognized, targeted, disease-specific testing should be pursued. Hemoglobinopathies are evaluated with hemoglobin electrophoresis or high-performance liquid chromatography, while suspected hereditary spherocytosis may be confirmed by osmotic fragility testing, eosin-5-maleimide binding by flow cytometry, or definitive molecular analysis of red blood cell membrane protein genes (SPTA1, SPTB, ANK1, SLC4A1, EPB42).

A clinical scenario that highlights the importance of hemoglobin electrophoresis occurs when patients present with anemia and microcytic indices, initially suggesting iron deficiency anemia. These patients may be started on iron therapy based on this impression. However, subsequent iron studies may reveal normal or even elevated iron levels, sometimes due to the iron supplementation already administered. Under these circumstances, hemoglobin electrophoresis should be performed to evaluate for thalassemia, which would allow discontinuation of unnecessary iron therapy. In suspected pyruvate kinase deficiency, current international guidelines recommend pyruvate kinase enzyme activity testing (preferably using a pyruvate kinase–to–hexokinase ratio) or PKLR gene analysis, with molecular confirmation of enzyme-based diagnoses.[58] The expert panel specifically recommends testing for pyruvate kinase deficiency in all patients with non-immune hemolytic anemia after excluding hemoglobin and erythrocyte membrane disorders.

Ancillary testing complements morphologic evaluation when poikilocytosis raises concern for underlying marrow or systemic disease. Flow cytometry, immunohistochemistry, molecular studies, fluorescence in situ hybridization, and cytogenetics should be used when hematologic neoplasms are suspected. Bone marrow aspirate and biopsy are indicated when peripheral findings suggest dyserythropoiesis or marrow pathology, or when initial testing is nondiagnostic. In patients with splenomegaly, additional evaluation may include abdominal imaging, Epstein–Barr virus testing when clinically indicated, and assessment for autoimmune hemolysis with direct antiglobulin testing and hemolysis markers.

In selected clinical settings, additional testing may be indicated. In patients from endemic regions with poikilocytosis and systemic symptoms, peripheral smear evaluation for malaria or babesiosis is recommended, with polymerase chain reaction testing used for confirmation when needed.[59][60] Suspected hereditary membrane disorders may require genetic or specialized membrane protein testing, with diagnostic strategies tailored to clinical context, family history, and geographic background.

Treatment / Management

Treatment of poikilocytosis is directed at the underlying etiology. When poikilocytosis results from nutritional anemias, such as iron deficiency or megaloblastic anemia due to vitamin B12 or folate deficiency, management includes targeted supplementation and correction of dietary deficiencies, along with treatment of contributing conditions such as malabsorption syndromes or alcohol use disorder.[61] Inherited causes of poikilocytosis, such as thalassemia or sickle cell disease, often require long-term management with lifelong monitoring, supportive care, and treatment of disease exacerbations, including transfusions or, in select cases, hematopoietic stem cell transplantation.

Acquired forms are managed by treating the underlying condition (eg, liver transplantation for advanced liver disease or antibiotics for sepsis). When schistocytes are present and thrombotic microangiopathy is suspected, urgent etiology-directed therapy, such as plasma exchange for thrombotic thrombocytopenic purpura, is required to reduce morbidity and mortality. In sickle cell disease, treatment includes disease-modifying therapies such as hydroxyurea and newer agents targeting vaso-occlusive pathways. More recently, gene-based therapies have emerged as options for selected patients with severe sickle cell disease and transfusion-dependent thalassemia.[62][63]

Differential Diagnosis

The differential diagnosis of poikilocytosis is broad and reflects a wide range of inherited and acquired disorders affecting RBC structure, hemoglobin composition, and marrow function (see Table 3). Accurate interpretation of poikilocyte patterns on peripheral smear, integrated with clinical context and laboratory findings, is essential for narrowing the diagnosis and guiding targeted evaluation. 

Table

Table 3. Differential Diagnosis Poikilocytosis.

DNA, deoxyribonucleic acid; G6PD, glucose-6-phosphate dehydrogenase; RBC, red blood cell; RNA, ribonucleic acid

Prognosis

The prognosis of poikilocytosis depends on the underlying etiology. Nutritional anemias, such as iron deficiency and megaloblastic anemia, generally have a favorable prognosis with correction of deficiencies, whereas inherited disorders, such as sickle cell disease and thalassemia, have variable long-term outcomes depending on disease severity, complication burden, and access to advanced therapies. Notably, recent advances, including gene-based treatments for sickle cell disease, represent a major therapeutic development with the potential to improve outcomes in selected patients. When poikilocytosis includes schistocytes, the prognosis may initially be guarded, as this finding can indicate thrombotic microangiopathy, in which delays in recognition and treatment markedly increase morbidity and mortality; prompt, etiology-directed therapy significantly improves outcomes. In addition, poikilocytosis associated with advanced liver disease—particularly spur cell anemia with acanthocytes—is linked to high short-term mortality unless definitive management, such as liver transplantation, is undertaken.[8]

Complications

Complications of poikilocytosis vary depending on the underlying etiology and may be overshadowed by the severity of the primary disease. In some cases, systemic illness or advanced organ dysfunction can obscure the contribution of disordered erythropoiesis. Careful clinical assessment and correlation with peripheral smear findings make poikilocytosis a valuable diagnostic clue. Common complications associated with major causes of poikilocytosis include the following:

• Sickle cell disease:

  • Infections
  • Osteomyelitis
  • Stroke, priapism
  • Acute chest syndrome
  • Hemolytic crisis
  • Aplastic crisis
  • Chronic kidney disease (sickle nephropathy)
  • Pulmonary hypertension
  • Avascular necrosis (especially femoral head)
  • Retinopathy or vision loss
  • Splenic sequestration crisis, autosplenectomy (seen in sickle cell disease) [71]
• Hereditary spherocytosis:

  • Folate deficiency (might be a functional deficit)
  • Hemolysis
  • Pigmented gallstones
  • Aplastic crisis 
• Thalassemia complications include:

  • Iron overload (from transfusions and/or increased absorption)
  • Cardiomyopathy and arrhythmias due to iron deposition
  • Liver dysfunction/cirrhosis (secondary hemochromatosis)
  • Endocrinopathies (diabetes, hypogonadism, hypothyroidism)
  • Growth delay and delayed puberty
• Present schistocytes with thrombotic microangiopathy etiology:

  • Acute kidney injury
  • Neurologic symptoms (confusion, seizures)
  • Multiorgan failure
  • Death if diagnosis and treatment are delayed
• Iron deficiency anemia:

  • Cognitive impairment and developmental delay in children
  • Restless legs syndrome
  • Reduced exercise tolerance
  • Pregnancy complications (preterm delivery, low birth weight)

Deterrence and Patient Education

Patient education regarding poikilocytosis focuses on the underlying etiology, as abnormal red blood cell morphology represents a laboratory finding rather than a disease. Educational efforts should be tailored to the specific cause, with hereditary hemoglobinopathies such as sickle cell disease and thalassemia requiring particularly comprehensive patient and family education. Preventive care in hemoglobinopathies includes adherence to recommended immunizations, folic acid supplementation, malaria prophylaxis in endemic areas, and regular surveillance for disease-related complications. Patient education should emphasize medication adherence, particularly to disease-modifying therapies such as hydroxyurea in sickle cell disease, which reduces vaso-occlusive events, acute chest syndrome, hospitalizations, and transfusion requirements. Overall, education aims to reinforce that these conditions are manageable with consistent, proactive care to optimize long-term outcomes.

Pearls and Other Issues

Key facts to keep in mind about poikilocytosis include the following:

• Poikilocytosis refers to abnormal RBC shape and is a peripheral smear finding, not a diagnosis.

  • This is generally defined as ≥10% of RBCs showing abnormal morphology.
• Poikilocytosis reflects an underlying disease affecting hemoglobin structure, membrane integrity, or bone marrow function.
• Spherocytes suggest hereditary spherocytosis or autoimmune hemolytic anemia (often Coombs-positive).
• Schistocytes indicate mechanical RBC destruction and are a key marker of thrombotic microangiopathy; >1% is concerning.
• Target cells (codocytes) are seen in thalassemia, liver disease, HbC disease, and post-splenectomy states.
• Sickle cells (drepanocytes) result from HbS polymerization under hypoxia.
• Dacrocytes (teardrop cells) suggest bone marrow fibrosis or infiltration.
• Echinocytes are often reversible and associated with uremia or electrolyte abnormalities.
• Acanthocytes are linked to advanced liver disease and abetalipoproteinemia.
• Bite cells point to oxidative hemolysis, classically G6PD deficiency.
• Always exclude smear artifacts before diagnosing true poikilocytosis.
• Management focuses on treating the underlying cause, not the morphology itself.
• The presence of schistocytes, anemia, and thrombocytopenia requires urgent evaluation.

Enhancing Healthcare Team Outcomes

Patients with poikilocytosis are at risk for complications related to the underlying systemic or hematologic disorder responsible for the abnormal RBC morphology. Early recognition of poikilocytosis on peripheral blood smear and timely evaluation of its etiology are essential to prevent diagnostic delays and reduce morbidity. Care of patients with poikilocytosis requires a collaborative, patient-centered approach involving primary care clinicians, hematologists, hematopathologists, nurses, pharmacists, and other health professionals to ensure accurate diagnosis and appropriate management. These clinicians must be proficient in recognizing characteristic smear patterns, interpreting laboratory studies, and understanding disease-specific diagnostic pathways to guide targeted therapy.

A strategic, evidence-based approach is critical, emphasizing prompt identification of high-risk conditions such as thrombotic microangiopathy, severe hemolytic anemias, or marrow failure syndromes. Ethical principles, including informed consent and shared decision-making, should guide discussions about diagnostic testing, transfusion therapy, and advanced treatments such as stem cell transplantation or gene-based therapies. Clear delineation of professional roles, effective interprofessional communication, and coordinated care planning are essential to ensure safe transitions across diagnostic evaluation, treatment, and longitudinal follow-up. Patient and caregiver education regarding disease cause, prognosis, treatment adherence, and warning symptoms that require urgent medical attention further supports optimal outcomes. Through coordinated interprofessional care, healthcare teams can improve diagnostic accuracy, reduce complications, and enhance outcomes for patients with poikilocytosis.

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Disclosure: Sai Samyuktha Bandaru declares no relevant financial relationships with ineligible companies.

Disclosure: Robert Killeen declares no relevant financial relationships with ineligible companies.