Differential Diagnosis
The patient's presentation of low C3 and C8, anemia, and high IgG suggests an immune-mediated process. Here's a categorized differential diagnosis:
Single most likely diagnosis
- Systemic Lupus Erythematosus (SLE): This autoimmune disease is known for its association with low complement levels (C3 and C4), anemia, and elevated IgG levels. The combination of these laboratory findings, along with the clinical presentation, makes SLE a strong candidate.
Other Likely diagnoses
- Rheumatoid Arthritis (RA): Although RA is more commonly associated with low C3 and C4, some patients may have low C8 levels. The presence of anemia and high IgG levels also supports this diagnosis.
- Sjögren's Syndrome: This autoimmune disorder can present with low complement levels, anemia, and elevated IgG. However, it is less likely than SLE given the specific combination of laboratory findings.
- Chronic Lymphocytic Leukemia (CLL): CLL can cause anemia and elevated IgG levels. While it is less likely to cause low C3 and C8, some patients may have immune-mediated complications that lead to these laboratory findings.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Hemophagocytic Lymphohistiocytosis (HLH): This rare and life-threatening condition can present with anemia, elevated IgG, and low complement levels. Although it is unlikely, missing this diagnosis could be fatal.
- Paroxysmal Nocturnal Hemoglobinuria (PNH): PNH is a rare disease that can cause anemia, elevated IgG, and low complement levels. It is essential to consider this diagnosis due to its potential for severe complications.
Rare diagnoses
- Cold Agglutinin Disease: This rare autoimmune disorder can cause anemia and elevated IgG levels. While it is less likely to cause low C3 and C8, some patients may have co-existing conditions that lead to these laboratory findings.
- Autoimmune Hemolytic Anemia (AIHA) with complement activation: AIHA can cause anemia and elevated IgG levels. In some cases, complement activation may lead to low C3 and C8 levels, although this is less common.