What is the approach to work up rouleaux (rouleaux formation) in a blood smear?

Diagnostic Approach to Rouleaux Formation in Blood Smear

When rouleaux formation is identified on a peripheral blood smear, the diagnostic workup should focus on evaluating for plasma cell disorders, particularly multiple myeloma, as this is the most clinically significant cause requiring prompt intervention. 1

Initial Evaluation

• Perform a complete blood count with differential and review the peripheral blood smear for additional findings such as circulating plasma cells, which may accompany rouleaux formation 1
• Order a comprehensive biochemistry panel including liver function tests, renal function tests, electrolytes, calcium, and albumin 1
• Distinguish true rouleaux from agglutination by performing a saline replacement test - rouleaux will disperse when plasma is replaced with saline, while true agglutination will persist 2

Specific Testing for Plasma Cell Disorders

• Evaluate both serum and urine for monoclonal proteins using:

  • Serum protein electrophoresis (SPEP) and urine protein electrophoresis (UPEP) 1
  • Immunofixation electrophoresis of serum and urine 1
  • Serum free light chain assay 1
  • Quantitative immunoglobulins by nephelometry 1

• If monoclonal protein is detected, proceed with:

  • Bone marrow aspiration and biopsy to assess for clonal plasma cells 1
  • Skeletal survey, low-dose whole-body CT, MRI, or PET-CT to evaluate for bone lesions 1

Interpretation of Results

• Diagnose multiple myeloma if the following criteria are met:

  • ≥10% clonal bone marrow plasma cells 1
  • Presence of serum and/or urinary monoclonal protein 1
  • Evidence of end-organ damage (hypercalcemia, renal insufficiency, anemia, bone lesions) 1

• Diagnose smoldering multiple myeloma if:

  • Serum monoclonal protein ≥3 g/dL and/or ≥10% clonal bone marrow plasma cells 1
  • Absence of end-organ damage 1

• Diagnose monoclonal gammopathy of undetermined significance (MGUS) if:

  • Serum monoclonal protein <3 g/dL 1
  • <10% clonal bone marrow plasma cells 1
  • Absence of end-organ damage 1

Other Causes of Rouleaux Formation

• If plasma cell disorder evaluation is negative, consider other causes of increased plasma proteins:

  • Chronic inflammatory conditions 3, 2
  • Connective tissue diseases 3, 2
  • Infections 3, 2
  • Pregnancy 3, 2

• In sickle cell trait patients, rouleaux formation may be more pronounced, especially in acidotic conditions, which could increase risk of intravascular sludging 4

Clinical Pearls and Pitfalls

• Rouleaux formation appears microscopically as red blood cells stacked together like coins and is distinct from true agglutination 3, 2
• The degree of rouleaux formation correlates with the concentration and molecular weight of plasma proteins 5, 6
• Recent blood transfusions can affect the interpretation of blood smear findings 3
• Nephelometric quantitation may overestimate monoclonal protein concentration when values are high 1
• Never delay appropriate workup when rouleaux is identified, as it may be the first indication of a plasma cell dyscrasia requiring urgent intervention 1