Differential Diagnosis for Underlying Glomerulonephritis (GN) with Low C3
Single Most Likely Diagnosis
- Post-Streptococcal Glomerulonephritis (PSGN): This is often considered the most common cause of low C3 levels in the context of GN, especially following a streptococcal infection. The low C3 level is due to the activation of the alternative complement pathway.
Other Likely Diagnoses
- Membranoproliferative Glomerulonephritis (MPGN): This condition is known for its association with persistent complement activation, leading to low C3 levels. It can be primary (idiopathic) or secondary to other conditions such as infections or autoimmune diseases.
- Lupus Nephritis: Systemic Lupus Erythematosus (SLE) can cause GN and is associated with low C3 and C4 levels due to the consumption of complement components in the immune complex formation.
- Shiga Toxin-associated Hemolytic Uremic Syndrome (HUS): Although more commonly associated with acute kidney injury, some cases can present with features of GN and low C3 levels due to the alternative pathway activation.
Do Not Miss Diagnoses
- Atypical Hemolytic Uremic Syndrome (aHUS): A rare but critical diagnosis to consider, as it can present with low C3 levels and has a high mortality rate if not promptly treated with eculizumab.
- Thrombotic Thrombocytopenic Purpura (TTP): While not primarily a GN, TTP can have renal involvement and low C3 levels in some cases, making it a diagnosis not to miss due to its severe prognosis.
- Goodpasture Syndrome: Although complement levels are typically normal, the severity of the disease and its potential for rapid progression to renal failure make it a diagnosis that should not be overlooked.
Rare Diagnoses
- C3 Glomerulopathy: A rare group of disorders characterized by the dysregulation of the alternative complement pathway, leading to low C3 levels and GN.
- Factor H Deficiency: A rare genetic disorder that affects the regulation of the alternative complement pathway, resulting in low C3 levels and increased susceptibility to certain infections and GN.
- Dense Deposit Disease (DDD): A subtype of MPGN characterized by the accumulation of dense deposits in the glomerular basement membrane, often associated with low C3 levels.