The main factor in the development of acute glomerulonephritis is: 1. Increase vascular permeability 2. Necrosis of the tubule epithelium 3. The formation of immune complexes 4. Fatty degeneration of the tubule epithelium 5. Hyalinosis of arterioles
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"acute glomerulonephritis" AND "immune complex" AND pathogenesis
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Answer: 3. The formation of immune complexes
Why immune complex formation is the central mechanism
Acute glomerulonephritis (AGN) - most classically, post-streptococcal glomerulonephritis (PSGN) - is the prototype of immune complex-mediated renal disease. The pathogenesis revolves around the deposition or formation of antigen-antibody (immune) complexes within the glomerular capillary wall, triggering a cascade of inflammatory injury.
Mechanisms of immune complex involvement:
- Planted antigen mechanism - Streptococcal antigens (e.g., nephritogenic SPEB/zymogen or GAPDH/NaPlr) deposit in the glomerulus first, then circulating antibodies bind in situ
- Circulating immune complex deposition - Pre-formed antigen-antibody complexes are trapped in the glomerular filtration apparatus
- Antigenic mimicry / autoimmune cross-reactivity - Streptococcal M proteins share epitopes with glomerular antigens (e.g., mesangial vimentin), triggering an autoreactive response
- Complement activation - Deposited immune complexes activate the complement cascade (particularly the alternative pathway), recruiting neutrophils and causing the characteristic inflammatory proliferative injury
The result is diffuse proliferative glomerulonephritis with mesangial and endocapillary hypercellularity, and on immunofluorescence, granular "starry-sky" deposits of IgG and C3 along the glomerular basement membrane.
Why the other options are wrong
| Option | Why Incorrect |
|---|---|
| 1. Increased vascular permeability | This is a consequence of inflammation, not the primary initiating event |
| 2. Necrosis of tubule epithelium | This describes acute tubular necrosis (ATN) - a different entity altogether |
| 4. Fatty degeneration of tubule epithelium | This is seen in nephrotic syndrome / tubular lipid accumulation, not AGN |
| 5. Hyalinosis of arterioles | This is a feature of hypertensive nephropathy and diabetic nephropathy - chronic conditions |
The answer is confirmed by Brenner and Rector's The Kidney: immune complex-mediated injury is the fundamental pathogenic mechanism in acute glomerulonephritis, whether via circulating complex deposition, planted antigens, or autoimmune cross-reactivity - all converging on complement activation and glomerular inflammation.
What is the symptom typical of acute in contrast to chronic glomerulonephritis: 1. proteinuria 2. hematuria 3. cylindruria 4.normostenuria 5.bacteriuria
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Answer: 2. Hematuria
Why hematuria is the distinguishing feature of ACUTE glomerulonephritis
Acute GN presents with the classic triad of:
- Hematuria (gross/macroscopic - "smoky," "cola-colored," or "tea-colored" urine) - the hallmark
- Oliguria
- Hypertension + edema
Hematuria - especially macroscopic (gross) hematuria with dysmorphic red cells and RBC casts - is the defining, dramatic feature of the acute nephritic syndrome. It reflects active, intense glomerular inflammation with disruption of the capillary wall allowing red cells to escape into the tubular filtrate.
Per the Tietz Textbook of Laboratory Medicine: "In acute glomerulonephritis, hematuria may lead to coloration of the urine and the presence of large numbers of red cells and white cells; as the duration of the disease increases, the amount of sediment diminishes."
This is the key point - as disease transitions from acute to chronic, hematuria decreases and eventually disappears, while other features persist.
Comparison: Acute vs. Chronic GN
| Feature | Acute GN | Chronic GN |
|---|---|---|
| Hematuria (gross) | Prominent - "smoky" urine | Mild/absent - sediment diminishes |
| Proteinuria | Present (usually mild, <1-2 g/day) | Present (often heavy, progressive) |
| Cylindruria (casts) | RBC casts present acutely | Waxy/broad casts (late fibrosis) |
| Normostenuria (fixed SG ~1.010) | Absent | Present - reflects lost concentrating ability |
| Bacteriuria | Absent (not an infectious-urine disease) | Absent |
Why the other options are wrong
- 1. Proteinuria - present in BOTH acute and chronic GN; not distinguishing
- 3. Cylindruria - casts occur in both (RBC casts in acute; waxy/broad casts in chronic)
- 4. Normostenuria - fixed urine specific gravity (isosthenuria/normostenuria) is a feature of chronic GN with tubular and concentrating function loss, not acute
- 5. Bacteriuria - not a feature of GN at all; this is characteristic of urinary tract infection/pyelonephritis
Gross hematuria - the "smoky urine" - is so characteristic of acute GN that its absence should prompt reconsideration of the diagnosis. In chronic GN, the inflammatory activity wanes, and hematuria fades as the dominant feature. (Robbins Pathologic Basis of Disease; Tietz Textbook of Laboratory Medicine)
A 26-year-old man with exacerbation of pulmonary tuberculosis. He received repeated chemotherapy: rifampicin, isoniazid and pyrazinamide. B.P. 130/90 mm Hg For 6 months periodically in the general analysis of urine: protein 0.33 g / l, white blood cells 8-10 in s / sp, red blood cells 4-5 in s / sp. LH: creatinine 100-120 μmol / l, urea 8-12 mmol / l, protein about 65 g / l, cholesterol 4.8 mmol / l. Ultrasound of the kidneys: PP 12.5x4.5, LP 12.9x4.6, parenchyma echogenicity is increased. What is the MOST probable diagnosis and main method for evaluating kidney function? 1.HBP, calculation of GFR according to Schwartz 2. Tuberculosis of the kidneys, excretory urography 3. Chronic glomerulonephritis, creatinine clearance 4.HBP, calculation of GFR according to CKD-EPI 5. Chronic interstitial nephritis, Zimnitsky test
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Answer: 5. Chronic interstitial nephritis, Zimnitsky test
Clinical analysis - why this is chronic interstitial nephritis (CIN)
Let's break down each clue in this case:
Patient context:
- 26-year-old man, pulmonary TB, receiving rifampicin + isoniazid + pyrazinamide (repeated/prolonged chemotherapy)
- Duration: 6 months of persistent findings
Urinalysis findings (pointing to tubular, NOT glomerular disease):
- Proteinuria 0.33 g/L - mild, low-grade (tubular proteinuria, typically <1 g/day in CIN)
- Leukocyturia 8-10/hpf - mild, "inactive" sediment
- Microhematuria 4-5/hpf - minimal
- No RBC casts, no nephrotic-range proteinuria
Blood work:
- Creatinine 100-120 μmol/L - mildly elevated
- Urea 8-12 mmol/L - mildly elevated
- Total protein 65 g/L - normal (rules out nephrotic syndrome)
- Cholesterol 4.8 mmol/L - normal (rules out nephrotic syndrome)
Ultrasound:
- Both kidneys mildly enlarged (12.5 and 12.9 cm length)
- Increased parenchymal echogenicity - classic sign of interstitial infiltration and fibrosis
BP 130/90 - mild hypertension, consistent with CIN (salt-sensitive hypertension is a feature)
This entire picture - mild tubular-pattern proteinuria, inactive sediment, tubular dysfunction, drugs known to cause interstitial injury, and increased echogenicity without glomerular features - is the signature of chronic drug-induced interstitial nephritis. Anti-TB drugs (rifampicin and pyrazinamide in particular) are well-documented causes of tubulointerstitial nephritis, as confirmed by Harrison's Principles of Internal Medicine 22E, which lists "interstitial nephritis" explicitly as a renal reaction to rifampicin.
Per Comprehensive Clinical Nephrology (7th ed.), the functional hallmarks of Chronic Interstitial Nephritis are:
- Insidious GFR deterioration
- Tubular proteinuria <1 g/day
- Inactive urinary sediment
- Medullary dysfunction - concentrating defects (nocturia, polyuria)
- Salt-sensitive hypertension
Why the Zimnitsky test is the correct functional test
The Zimnitsky (Zimnitzky) test measures urinary concentrating and diluting ability by collecting 8 separate 3-hour urine portions over 24 hours and measuring specific gravity in each. It directly assesses tubular (medullary) function.
In CIN, the primary functional defect is tubular concentrating impairment - the hallmark is isosthenuria/normostenuria (all urine portions have fixed specific gravity ~1.010-1.012), reflecting loss of medullary tubular function. This is the very defect the Zimnitsky test is designed to detect.
| Why NOT the other tests | Reasoning |
|---|---|
| GFR by Schwartz | Schwartz formula is for children (uses height); this is an adult |
| Excretory urography | Used for renal TB (structural changes, cavitation, calcifications); no findings suggest renal TB here - just drug toxicity |
| Creatinine clearance | Measures glomerular function (GFR); tubular dysfunction is the primary problem here, not glomerular |
| GFR by CKD-EPI | CKD-EPI estimates GFR (glomerular function); misses the tubular defect which is the core of CIN |
Why the other diagnoses are wrong
- Option 1 & 4 (HBP) - BP is only 130/90; mild elevation is a consequence of CIN, not the primary diagnosis. Hypertension alone does not explain the full picture.
- Option 2 (Renal TB) - Would require urinary acid-fast bacilli, structural kidney changes on imaging (cavitation, calcification, hydronephrosis), and symptoms of renal TB. The patient has pulmonary TB; the kidney findings are from drug toxicity, not infection of the kidney.
- Option 3 (Chronic GN) - Chronic GN would show more significant proteinuria, hematuria with dysmorphic RBCs/casts, and the profile would not match 6 months of anti-TB drug use so cleanly. Creatinine clearance tests glomerular function, not the tubular defect.
The answer is confirmed: repeated anti-TB chemotherapy (especially rifampicin) caused chronic interstitial nephritis, and the Zimnitsky test is the appropriate method to evaluate tubular concentrating function - the primary dysfunction in this condition. - Comprehensive Clinical Nephrology, 7th Edition
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