Nephrotic vs Nephritic Syndrome
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Direct answer
Nephrotic syndrome is the consequence of a leaky glomerular filter: heavy proteinuria of more than 3.5 g per day with hypoalbuminaemia, generalised oedema and hyperlipidaemia. Nephritic syndrome is the consequence of glomerular inflammation: haematuria with red cell casts, hypertension, oliguria and mild proteinuria. The degree of proteinuria and the presence of red cell casts separate the two at the bedside.
What you must remember
- Nephrotic features: periorbital then dependent pitting oedema, frothy urine, hypoalbuminaemia, hyperlipidaemia with oval fat bodies and fatty casts (Maltese crosses under polarised light).
- Nephrotic complications follow protein losses — hypogammaglobulinaemia with infection risk, loss of antithrombin III producing a hypercoagulable state and renal vein thrombosis, and vitamin D deficiency.
- Nephrotic causes: minimal change disease, the commonest in children, with foot process effacement on electron microscopy, a normal light microscopy and an excellent steroid response; membranous nephropathy, the commonest primary cause in adults; focal segmental glomerulosclerosis; and diabetic glomerulosclerosis, the leading secondary cause overall.
- Nephritic features: tea- or cola-coloured urine with dysmorphic erythrocytes and red cell casts, hypertension, oliguria, azotaemia and subnephrotic proteinuria; glomeruli are hypercellular with leukocyte influx.
- Nephritic causes: post-streptococcal glomerulonephritis of childhood, one to three weeks after streptococcal pharyngitis or impetigo, with a low C3; IgA nephropathy, the commonest glomerulonephritis worldwide, with haematuria within a day or two of a respiratory infection; rapidly progressive (crescentic) glomerulonephritis; and membranoproliferative glomerulonephritis.
- Management markers: minimal change disease responds to corticosteroids; post-streptococcal glomerulonephritis is treated supportively with salt restriction, diuretics and blood pressure control and carries an excellent prognosis in children.
- Work-up: urine microscopy for casts, serum albumin and lipids, complement C3, spot protein-creatinine ratio and renal biopsy for atypical or adult-onset nephrotic disease.
Common confusion
The classical error is calling every swollen child nephrotic and every red urine nephritic without checking proteinuria. Nephrotic syndrome is defined by proteinuria above 3.5 g per day — oedema is secondary; nephritic syndrome is defined by an active urine sediment with red cell casts. Timing also separates IgA nephropathy (haematuria within one to two days of a sore throat) from post-streptococcal disease (one to three weeks after).
Exam-focused takeaway
Theory answers should define both syndromes, list causes by age, and contrast the urine sediment, complement levels and complications. Viva examiners ask whether red cell casts occur in nephrotic syndrome (they do not) and why nephrotic patients thrombose. MCQs test foot process effacement in minimal change disease, antithrombin III loss with renal vein thrombosis, low C3 in post-streptococcal disease and synpharyngitic haematuria in IgA nephropathy.
Frequently asked questions
How much proteinuria defines nephrotic syndrome?
More than 3.5 g per day — heavy enough to cause hypoalbuminaemia, oedema and hyperlipidaemia.
What is the commonest cause of nephrotic syndrome in children?
Minimal change disease — normal light microscopy with foot process effacement on electron microscopy and a prompt response to corticosteroids.
Why are nephrotic patients hypercoagulable?
Urinary loss of antithrombin III and other natural anticoagulants, plus increased hepatic clotting factor synthesis, predisposes to venous thrombosis including renal vein thrombosis.
How does IgA nephropathy differ from post-streptococcal glomerulonephritis?
IgA nephropathy causes haematuria within one to two days of a respiratory infection with normal complement; post-streptococcal disease follows one to three weeks later with a low C3.
Are red cell casts found in nephrotic syndrome?
No — red cell casts signify an active nephritic sediment; nephrotic urine shows oval fat bodies and fatty casts instead.