Page 3 of 25

PA27.1-2 | Normal Kidney & Clinical Syndromes — SDL Guide (Part 3)

The Other Six Renal Clinical Syndromes

A six-panel infographic summarises asymptomatic urinary abnormalities, AKI, CKD, RPGN, UTI, and urinary obstruction using kidney, glomerular, and urinary tract diagrams. — **Panel A:** Urine dipstick, microscopic haematuria, subnephrotic proteinuria, thin basement membrane, IgA nephropathy, Alport syndrome.. **Panel B:** Rapid GFR decline, azotaemia, rising creatinine, rising urea, oliguria, pre-renal hypoperfusion, intrinsic renal injury, post-renal obstruction.. **Panel C:** Shrunken granular kidney, nephron loss, interstitial fibrosis, GFR <60 mL/min/1.73 m² for >3 months, uraemia, anaemia, renal osteodystrophy.. **Panel D:** Crescent in Bowman's space, compressed glomerular tuft, parietal epithelial proliferation, macrophages, anti-GBM disease, ANCA vasculitis, immune complex GN.. **Panel E:** Ascending bacteria, urethra, bladder cystitis, ureter, renal pelvis, pyelonephritis.. **Panel F:** Ureteric calculus, obstruction, hydroureter, hydronephrosis, dilated renal pelvis, back pressure..

1. Asymptomatic haematuria / proteinuria: Isolated urinary abnormalities without systemic features. Subnephrotic proteinuria (<1 g/day) or microscopic haematuria found incidentally. Common causes: IgA nephropathy (most common GN worldwide), thin basement membrane disease, early hereditary nephritis (Alport syndrome).

2. Acute kidney injury (AKI): Rapid (hours to days) decline in GFR producing azotaemia (rising creatinine and urea) with or without oliguria (<400 mL/day). Causes are classified as pre-renal (hypoperfusion), intrinsic renal (tubular, glomerular, interstitial, vascular), or post-renal (obstruction). The key question: is the kidney salvageable? (covered in SDL 3).

3. Chronic kidney disease (CKD): Progressive, usually irreversible loss of GFR over months to years. GFR <60 mL/min/1.73m² for >3 months defines CKD. Ultimately produces uraemia — the clinical syndrome of accumulation of nitrogenous waste products (urea, creatinine, guanidino compounds) causing encephalopathy, pericarditis, platelet dysfunction, anaemia (EPO deficiency), and renal osteodystrophy.

4. Rapidly progressive glomerulonephritis (RPGN): A nephritic syndrome that deteriorates to renal failure within weeks to months. Histological hallmark: crescents in >50% of glomeruli (proliferating parietal epithelial cells ± macrophages). A renal emergency. Causes: anti-GBM disease (Goodpasture), ANCA-associated vasculitis, immune complex GN.

5. Urinary tract infection (UTI): Dysuria, frequency, bacteriuria, pyuria (WBC casts if pyelonephritis). Not primarily a glomerular disease. WBC casts in urine → upper tract infection (pyelonephritis) or acute interstitial nephritis.

6. Nephrolithiasis (renal stones): Flank pain, haematuria, no proteinuria, no casts. Stones classified by composition: calcium oxalate/phosphate (most common), uric acid, struvite (infection stones), cystine.

Urinary Casts — Reading the Urine Microscopy

Diagram explaining how urinary casts form in renal tubules and how hyaline, RBC, WBC, granular, fatty, and waxy casts appear and relate to clinical disease. — **Panel A:** Tamm-Horsfall protein/uromodulin matrix, thick ascending limb of Henle, tubular lumen, precipitated proteins and cells, cylindrical cast molded by tubule shape. **Panel B:** Hyaline cast, RBC cast, WBC cast, granular cast, fatty cast / oval fat bodies, Maltese cross lipid droplets, waxy cast. **Panel C:** Normal or concentrated urine, glomerulonephritis/nephritic syndrome, pyelonephritis, acute interstitial nephritis, tubular injury/AKI, nephrotic syndrome, chronic kidney disease/renal failure.

Urinary casts are cylindrical structures formed when proteins or cells precipitate within the tubular lumen, moulded by the tubule shape. All casts have a Tamm-Horsfall protein (uromodulin) matrix secreted by the TAL of Henle.

Cast types and their clinical significance:

Cast type	Appearance	Significance
Hyaline casts	Pale, homogeneous	Non-specific; normal in small numbers, concentrated urine
RBC casts	Red-tinged, packed with RBCs	Pathognomonic of glomerulonephritis (nephritic syndrome)
WBC casts	White cells embedded	Pyelonephritis or acute interstitial nephritis
Granular casts	Coarse or fine granules	Non-specific tubular injury; in abundance → AKI
Fatty casts / oval fat bodies	Lipid droplets, Maltese cross	Nephrotic syndrome
Waxy / broad casts	Waxy, wide diameter	Advanced CKD — form in dilated atrophic tubules
Epithelial cell casts	Renal tubular cells	Acute tubular necrosis (ischaemic or toxic AKI)

IMG: urinary casts microscopy panel

Six side-by-side microscopy-style panels compare hyaline, RBC, WBC, granular, fatty, and broad waxy urinary casts with their key syndrome associations. — **Panel A:** Hyaline cast: transparent smooth cylindrical cast; association with normal exercise, dehydration, and pre-renal azotaemia.. **Panel B:** RBC cast: red blood cells embedded in a cast; association with nephritic syndrome and glomerulonephritis.. **Panel C:** WBC cast: leukocytes with multilobed nuclei inside a cast; association with pyelonephritis and interstitial nephritis.. **Panel D:** Granular cast: muddy brown coarse granular cast; association with acute tubular necrosis.. **Panel E:** Fatty cast: lipid droplets and oval fat bodies with polarised-light inset showing Maltese cross; association with nephrotic syndrome.. **Panel F:** Broad waxy cast: wide brittle cast with cracks and squared ends; association with chronic kidney disease and renal failure..

Azotaemia vs Uraemia — A Critical Distinction

A three-panel medical infographic distinguishes azotaemia as elevated BUN and creatinine from uraemia as a symptomatic multisystem syndrome of severe renal failure. — **Panel A:** Azotaemia: laboratory finding; BUN ↑; serum creatinine ↑; reduced GFR; asymptomatic by itself; Uraemia: clinical syndrome; toxin accumulation; unwell patient; GFR <10-15 mL/min.. **Panel B:** Pre-renal azotaemia: dehydration or reduced renal perfusion, BUN:Cr >20:1; intrinsic renal azotaemia: parenchymal disease, BUN:Cr 10-15:1; post-renal azotaemia: urinary tract obstruction.. **Panel C:** Neurological: encephalopathy, asterixis, peripheral neuropathy; cardiovascular: uraemic pericarditis, accelerated atherosclerosis; haematological: normocytic normochromic anaemia, platelet dysfunction; metabolic: hyperphosphataemia, secondary hyperparathyroidism, renal osteodystrophy, acidosis, hyperkalaemia; dermatological: uraemic frost, pruritus..

Two terms that are often conflated but have distinct meanings:

Azotaemia is a laboratory finding: elevated blood urea nitrogen (BUN) and serum creatinine reflecting reduced GFR. It is asymptomatic by itself and can be pre-renal (dehydration), renal (parenchymal disease), or post-renal (obstruction).

Uraemia is a clinical syndrome: the constellation of symptoms caused by accumulation of nitrogenous waste products and metabolic derangements when GFR falls to <10–15 mL/min. Features:
- Neurological: encephalopathy, asterixis, peripheral neuropathy
- Cardiovascular: uraemic pericarditis (friction rub), accelerated atherosclerosis
- Haematological: normochromic normocytic anaemia (↓ EPO), platelet dysfunction (bleeding tendency)
- Metabolic: hyperphosphataemia → secondary hyperparathyroidism → renal osteodystrophy; metabolic acidosis; hyperkalaemia
- Dermatological: uraemic frost (urea crystallisation on skin), pruritus

Mnemonic: Azotaemia = a lab value (BUN/Cr up). Uraemia = Unwell patient (symptoms of toxin accumulation).

Pre-renal azotaemia has a BUN:Cr ratio >20:1 (urea is reabsorbed passively with water in concentrated urine); intrinsic renal azotaemia has BUN:Cr ~10-15:1.

SELF-CHECK

A 55-year-old with longstanding diabetes presents with serum creatinine 6.8 mg/dL (baseline 1.0 mg/dL one year ago), BUN 98 mg/dL, haemoglobin 8.2 g/dL, and asterixis on exam. Which term BEST describes his condition?

A. Pre-renal azotaemia

B. Nephrotic syndrome

C. Asymptomatic azotaemia

D. Uraemia

Reveal Answer

Answer: D. Uraemia

This patient has symptomatic end-stage renal disease. Uraemia is the correct term because he has clinical manifestations (asterixis = metabolic encephalopathy, anaemia from EPO deficiency) caused by accumulation of nitrogenous waste products, not merely a lab abnormality. Pre-renal azotaemia would have a BUN:Cr >20:1 and respond to fluids. 'Asymptomatic azotaemia' is a contradiction here given his neurological and haematological findings. Nephrotic syndrome is characterised by massive proteinuria and oedema, not encephalopathy or anaemia.