Differential Diagnosis for Hematuria and Low C3

Single Most Likely Diagnosis

• Post-Streptococcal Glomerulonephritis (PSGN): This condition is a common cause of hematuria and low C3 levels, especially in children and young adults, following a streptococcal infection. The low C3 level is due to the consumption of complement during the immune response.

Other Likely Diagnoses

• Membranoproliferative Glomerulonephritis (MPGN): This is a type of glomerulonephritis characterized by changes in the glomeruli, including thickening of the capillary walls and proliferation of mesangial and endothelial cells. It can present with hematuria and low C3 levels due to complement activation.
• Lupus Nephritis: Systemic lupus erythematosus (SLE) can cause renal involvement, leading to hematuria. Low C3 levels are common in active SLE due to the consumption of complement by immune complexes.
• IgA Nephropathy (Berger's Disease): Although IgA nephropathy typically presents with normal complement levels, some cases can have low C3 levels, especially if there is an associated factor like factor H deficiency.

Do Not Miss Diagnoses

• Atypical Hemolytic Uremic Syndrome (aHUS): This is a rare but life-threatening condition characterized by hemolytic anemia, acute kidney injury, and low platelet count. Some forms of aHUS are associated with complement dysregulation, leading to low C3 levels. It's crucial to diagnose aHUS promptly due to its high mortality rate if untreated.
• Shiga Toxin-Associated Hemolytic Uremic Syndrome (STEC-HUS): Similar to aHUS, STEC-HUS can present with hematuria and acute kidney injury. While C3 levels are typically normal, the condition's severity and potential for renal failure make it a "do not miss" diagnosis.

Rare Diagnoses

• C3 Glomerulopathy: This includes a group of rare diseases characterized by the accumulation of complement factors in the glomeruli, leading to low C3 levels and renal dysfunction. It encompasses dense deposit disease and C3 glomerulonephritis.
• Factor H Deficiency: A rare genetic disorder leading to uncontrolled activation of the alternative complement pathway, resulting in low C3 levels and increased susceptibility to infections and renal disease.
• Membranous Nephropathy with Complement Activation: While membranous nephropathy typically presents with normal complement levels, some cases can have low C3 levels due to complement activation, especially if there is an underlying infection or autoimmune disease.