What is the next step in managing a patient with poikilocytosis, burr cells, and creatured Red Blood Cells (RBCs), potentially indicating impaired renal function?

Next Step for Poikilocytosis with Burr Cells and Crenated RBCs

Immediately assess renal function with serum creatinine, BUN, and calculated eGFR, as burr cells (echinocytes) and crenated RBCs strongly suggest uremia from renal insufficiency. 1

Immediate Laboratory Evaluation

The presence of burr cells and crenated RBCs points toward renal dysfunction as the primary etiology, requiring urgent assessment:

• Obtain renal function tests including serum creatinine, BUN, and calculated eGFR to evaluate for uremia, which is the most common cause of burr cell formation 1
• Review peripheral blood smear to quantify the degree of poikilocytosis and identify other morphologic abnormalities that may suggest alternative diagnoses 1
• Complete blood count with reticulocyte count to assess for concurrent anemia and determine if there is an appropriate bone marrow response 1, 2

Critical Differential Considerations

While renal insufficiency is the leading consideration with burr cells, you must exclude more urgent conditions:

Rule Out Thrombotic Microangiopathy (TMA)

• Look for schistocytes on the peripheral smear (fragmented RBCs distinct from burr cells), as their presence—even if rare—mandates immediate TMA workup 2
• If schistocytes are present with thrombocytopenia and elevated LDH, immediately order ADAMTS13 activity level and inhibitor titer before any treatment delays occur, as TTP mortality increases with delayed plasma exchange 2
• Obtain lactate dehydrogenase (LDH), haptoglobin, direct antiglobulin test (DAT), and bilirubin to assess for hemolysis 2

Assess for Malignancy

• Poikilocytosis occurs in 12% of cancer patients and is associated with poor prognosis, particularly in metastatic gastrointestinal adenocarcinoma 3
• Consider age-appropriate cancer screening if no obvious renal disease is identified and the patient has unexplained weight loss or constitutional symptoms 3

Concurrent Nephrologic Evaluation

If renal insufficiency is confirmed, concurrent nephrologic consultation is warranted to determine the underlying cause and guide management:

• The presence of renal dysfunction requires nephrologic work-up even if urologic evaluation is also needed for other findings like hematuria 1
• Evaluate urinalysis for proteinuria, hematuria, and cellular casts to distinguish glomerular from tubular disease 1
• Dysmorphic RBCs, proteinuria, or cellular casts indicate glomerular pathology requiring nephrology involvement 1

Additional Workup Based on Clinical Context

If Anemia is Present

• Check serum ferritin, vitamin B12, and folate only if there is high clinical suspicion (macrocytosis, neurologic symptoms), as deficiency rates are low in the general population 1
• Assess for hemolysis markers including indirect bilirubin and haptoglobin if reticulocytosis is present 2

If Cytopenia is Present

• Consider bone marrow evaluation if stable cytopenia persists for 2-6 months with no clear secondary cause, as myelodysplastic syndrome requires dysplasia in ≥10% of cells in at least one lineage 1
• Bone marrow aspiration with Prussian blue stain and cytogenetics should be obtained if MDS is suspected 1

Critical Pitfalls to Avoid

• Do not dismiss low-grade schistocytes (<1%) as insignificant, as early TMA can present with minimal fragmentation and test sensitivity is poor 2
• Do not delay plasma exchange while awaiting ADAMTS13 results if TTP is clinically suspected with the triad of hemolytic anemia, thrombocytopenia, and neurologic symptoms 2
• Do not assume anticoagulation or chronic catheterization explains the findings without completing appropriate urologic and nephrologic evaluation 1
• Renal dysfunction increases risk with contrast studies, so calculate eGFR before ordering any imaging that may require contrast or gadolinium 1