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

The Renal Clinical Syndromes — Framework Overview

A colour-coded renal syndrome flowchart uses haematuria, proteinuria, urinary casts, and azotaemia to classify eight major renal clinical syndromes.

Urinalysis Framework for Renal Clinical Syndromes

Panel A: Decision flowchart mapping haematuria, proteinuria, urinary casts, and azotaemia rate to nephritic syndrome, rapidly progressive GN, nephrotic syndrome, asymptomatic urinary abnormality, acute kidney injury, chronic kidney disease, urinary tract infection, and tubular / interstitial syndrome.. Panel B: Four urinalysis anchor parameters: haematuria, proteinuria, urinary casts, and azotaemia, each shown with a simple labelled icon.. Panel C: Simplified glomerular inflammation mechanism showing damaged capillary wall, dysmorphic RBC passage, protein leak, reduced GFR, and RBC cast formation..

A renal clinical syndrome is a constellation of signs, symptoms, and urinalysis findings that points to a pathophysiological mechanism and a disease category — before histology is available. Eight syndromes cover nearly all renal presentations. Mastering them lets you generate a differential before the biopsy report arrives.

The framework rests on four urinalysis parameters:
1. Haematuria (RBCs in urine) — present/absent; dysmorphic RBCs indicate glomerular origin.
2. Proteinuria — subnephrotic (<3.5 g/day) vs nephrotic-range (>3.5 g/day).
3. Urinary casts — cylindrical moulds formed in tubular lumina; their cellular content identifies the injury zone.
4. Azotaemia — elevated serum creatinine/urea indicating reduced GFR; rate of rise distinguishes AKI from CKD.

IMG: syndrome classification map

A colour-coded renal pathology decision flowchart maps haematuria with RBC casts, massive proteinuria, and azotaemia rate to eight renal clinical syndromes.

Urinalysis Decision Flowchart for Renal Clinical Syndromes

Panel A: Main diagnostic branches: haematuria + RBC casts, massive proteinuria >3.5 g/day, azotaemia rate; outcomes include nephritic syndrome, rapidly progressive GN, nephrotic syndrome, asymptomatic haematuria/proteinuria, acute kidney injury, chronic kidney disease, tubulointerstitial syndrome, and urinary tract infection / pyelonephritis.. Panel B: Simplified glomerular capillary cross-section showing nephritic inflammation with RBC leakage and RBC cast formation versus nephrotic podocyte injury with albumin leakage.. Panel C: Colour legend and urinalysis key: red nephritic group, blue nephrotic group, green mixed/other syndromes; symbols for RBC cast, oval fat body, protein dipstick, and creatinine trend line..

Nephritic Syndrome

Nephritic syndrome is the prototypical presentation of glomerular inflammation. Inflammation disrupts capillary walls, allowing RBCs and protein to leak while reducing GFR.

Hallmark features (all five must be considered):
- Haematuria — macroscopic (tea-coloured or smoky urine) or microscopic; dysmorphic RBCs (acanthocytes) indicate passage through the damaged GBM.
- RBC casts in urine — pathognomonic of glomerulonephritis. RBCs trapped in Tamm-Horsfall protein matrix within the tubule lumen form cylindrical casts.
- Mild-to-moderate proteinuria — typically <3.5 g/day; the GBM is inflamed but not completely destroyed.
- Hypertension — due to Na⁺/water retention from reduced GFR + RAAS activation.
- Oliguria and azotaemia — reduced urine output and rising creatinine from fall in GFR.

Prototype diseases: post-streptococcal GN, IgA nephropathy (Berger disease), lupus nephritis (Class III/IV), membranoproliferative GN.

Key distinction: In nephritic syndrome the problem is inflammation reducing filtration, so haematuria and azotaemia dominate. Proteinuria is secondary, not massive.

Nephrotic Syndrome

Diagram showing nephrotic syndrome as non-inflammatory glomerular filtration barrier dysfunction causing massive proteinuria, hypoalbuminaemia, oedema, hyperlipidaemia, lipiduria, and comparison with nephritic syndrome.

Nephrotic Syndrome: Barrier Dysfunction and Consequences

Panel A: Glomerular capillary loop, fenestrated endothelium, glomerular basement membrane, negatively charged filtration barrier, podocyte foot processes, Bowman's space, albumin leak, massive proteinuria >3.5 g/day, no inflammatory cells.. Panel B: Massive proteinuria, hypoalbuminaemia, reduced plasma oncotic pressure, generalized oedema, periorbital oedema, ascites, pleural effusion, hepatic lipoprotein synthesis, hyperlipidaemia, lipiduria, oval fat bodies, Maltese cross pattern.. Panel C: Nephritic syndrome: inflamed glomerulus, haematuria, RBC casts, mild proteinuria, hypertension, oliguria. Nephrotic syndrome: non-inflamed GBM/podocyte dysfunction, heavy proteinuria, oedema, hyperlipidaemia/lipiduria, absent or minimal haematuria and RBC casts..

Nephrotic syndrome results from glomerular diseases that disrupt the filtration barrier's permselectivity — particularly the charge barrier — without (initially) causing inflammation.

Four defining features:
- Massive proteinuria >3.5 g/day (in practice >3 g/day in adults) — the sine qua non.
- Hypoalbuminaemia — albumin lost in urine faster than the liver can synthesise it.
- Generalised oedema — reduced plasma oncotic pressure; fluid shifts to the interstitium (periorbital oedema, ascites, pleural effusion).
- Hyperlipidaemia and lipiduria — compensatory hepatic lipoprotein synthesis; lipid casts and oval fat bodies (Maltese cross pattern under polarised light) in urine.

Additional complications: hypercoagulability (antithrombin III lost in urine → renal vein thrombosis), susceptibility to encapsulated organism infections (IgG lost), vitamin D deficiency (vitamin D–binding protein lost).

Prototype diseases: Minimal change disease (children), focal segmental glomerulosclerosis (FSGS; adults), membranous nephropathy, diabetic nephropathy (advanced).

Key distinction: In nephrotic syndrome the GBM/podocytes are functionally disrupted but not inflamed — haematuria and RBC casts are absent or minimal. Proteinuria and its downstream consequences dominate.

IMG: nephritic vs nephrotic comparison

A side-by-side medical diagram compares nephritic syndrome with haematuria and RBC casts against nephrotic syndrome with massive proteinuria, oedema, lipiduria, and typical urinalysis strip results.

Nephritic vs Nephrotic Syndrome

Panel A: Inflamed glomerulus, red blood cells crossing the filtration barrier, RBC cast in tubule, haematuria, mild proteinuria, hypertension, oliguria. Panel B: Podocyte foot process effacement, albumin leakage, oedema, hypoalbuminaemia, hyperlipidaemia, lipid droplets, oval fat bodies, Maltese cross inset, absence of RBC casts. Panel C: Nephritic urinalysis strip showing blood 3+, protein 1+ to 2+, RBC casts; nephrotic urinalysis strip showing protein 4+, blood negative, oval fat bodies / Maltese cross.

SELF-CHECK

A 6-year-old boy presents with puffy eyes on waking and frothy urine. His urine dipstick shows 4+ protein with no blood. Serum albumin is 1.8 g/dL. Which urinalysis finding would be MOST characteristic of his condition?

A. RBC casts

B. Granular casts

C. Oval fat bodies (Maltese cross under polarised light)

D. WBC casts

Reveal Answer

Answer: C. Oval fat bodies (Maltese cross under polarised light)

This is classic nephrotic syndrome (massive proteinuria, hypoalbuminaemia, oedema). The hallmark urinary finding in nephrotic syndrome is lipiduria — oval fat bodies derived from tubular reabsorption of filtered lipoproteins; they show a Maltese cross birefringence pattern under polarised light. RBC casts indicate glomerular inflammation (nephritic). WBC casts suggest pyelonephritis or interstitial nephritis. Granular casts are non-specific and appear in many tubular injuries.