I am referred occasional otherwise healthy patients for evaluation of lymphopenia (aka lymphocytopenia).
What to do?
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1. Let's begin with definitions - lymphopenia is usually defined as an absolute lymphocyte count ALC <1000 cells/microL for adults
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2. Epidemiology - lymphopenia has been documented in 1.5-3% of CBCs from both community and hospitalized patients.
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3. Causes/associated conditions - lymphopenia may be found incidentally in someone without obvious underlying cause (most common) or may be associated with a number of diseases/conditions.
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4. Mechanisms - reduced production, increased destruction, increased apoptosis, redistribution of lymphocytes between blood and various lymphoid tissues.
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5. Clinical implications - no evidence (outside of large population studies that do not take into account underlying cause) that lymphopenia associated with increased risk of infection.
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6. History and physical - focus on symptoms/signs associated with underlying cause/associated conditions(s).
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7. Lab tests - generally not needed in an otherwise healthy individual.
8. Treatment - directed towards the underlying cause.
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Patients with SLE can present with a staggering array of hematologic abnormalities. Virtually no component of the blood is spared. Everything is fair game:
Have you ever wondered why plasma exchange saves lives in TTP but does nothing in ITP? Both are IgG-mediated. So why the difference?
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In ITP, antibodies opsonize platelets. Even if you remove some by exchange, IgG quickly re-equilibrates from the extravascular pool and continues to be produced. With no missing factor to replace, there’s no lasting benefit.
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In TTP, antibodies inhibit ADAMTS13. Plasma exchange not only removes antibody but also replaces the missing enzyme (and helps clear ULVWF multimers). That dual action is why it works.