Final Answer:
The three nephritic syndromes associated with decreased C3 levels are poststreptococcal glomerulonephritis, membranoproliferative glomerulonephritis (MPGN), and IgA nephropathy.
Step-by-step explanation:
Nephritic syndromes are a group of kidney disorders characterized by inflammation of the renal glomeruli. A common immunological feature in some nephritic syndromes is the reduction in complement component C3 levels. Poststreptococcal glomerulonephritis (PSGN) is often triggered by a streptococcal infection and is associated with low C3 levels. In PSGN, the immune system produces antibodies that form immune complexes, activating the complement system and leading to C3 consumption.
Membranoproliferative glomerulonephritis (MPGN) is another nephritic syndrome where C3 levels are frequently decreased. MPGN is characterized by immune complex deposition in the glomerular basement membrane, activating the complement cascade and resulting in reduced C3 levels. Lastly, IgA nephropathy is a form of glomerulonephritis where IgA immune complexes deposit in the glomeruli, leading to inflammation and decreased C3 levels. The immune complexes activate the alternative complement pathway, contributing to C3 consumption.
The measurement of complement components, including C3, is essential in diagnosing and monitoring nephritic syndromes. The decrease in C3 levels indicates ongoing complement activation and immune complex-mediated damage to the kidneys. Understanding the association between specific nephritic syndromes and decreased C3 levels is crucial for clinicians in guiding diagnostic and therapeutic approaches for patients with kidney disorders.