Nephritic Syndrome — Clinical

A 35-year-old woman with a known history of systemic lupus erythematosus (SLE) presents with gross haematuria, proteinuria (2.5 g/day), and hypertension for 2 weeks. Serum creatinine is 1.8 mg/dL. Anti-dsDNA antibodies are strongly positive, and complement C3 and C4 levels are low. Which investigation is most appropriate to determine the class of lupus nephritis and guide treatment decisions?

A 28-year-old man presents with sudden onset hematuria, mild hypertension (BP 145/92 mmHg), and mild proteinuria. Serum creatinine is 1.2 mg/dL. Serological workup shows elevated anti-streptolysin O (ASO) titre and low C3 levels. Kidney biopsy confirms post-streptococcal glomerulonephritis (PSGN). What is the drug of choice for management of hypertension in this patient?

A 28-year-old Indian male presents with sudden onset haematuria, hypertension (160/100 mmHg), and mild oedema 2 weeks after a sore throat. Urinalysis shows RBC casts and dysmorphic RBCs. What is the most common cause of acute nephritic syndrome in this clinical scenario?

A 28-year-old man presents with sudden onset haematuria, mild periorbital oedema, and hypertension (BP 148/92 mmHg) for 3 days. Urine dipstick shows 3+ protein and 4+ blood. Serum creatinine is 1.2 mg/dL (baseline 0.8 mg/dL). Complement C3 levels are low. Which investigation is most specific for confirming the diagnosis of post-infectious glomerulonephritis?

A 28-year-old man presents with sudden-onset hematuria, hypertension, and mild renal dysfunction 10 days after a sore throat. Serum complement C3 is low, and anti-GBM antibody is negative. Which single feature best distinguishes post-infectious glomerulonephritis (PIGN) from IgA nephropathy in this clinical context?