**Question:** In Nephrotic syndrome, all serum proteins are reduced except

A. Albumin
B. Immunoglobulins
C. Transferrin
D. Haptoglobin

**Core Concept:** Nephrotic syndrome is a clinical condition characterized by severe proteinuria, hypoalbuminemia, hyperlipidemia, and edema. These symptoms are the result of kidney damage, typically due to glomerulopathies like minimal change disease, focal segmental glomerulosclerosis, or membranous nephropathy.

**Why the Correct Answer is Right:** In nephrotic syndrome, there is a massive loss of proteins in the urine due to renal tubular dysfunction and podocytopathy. The body tries to compensate for this loss by increasing protein synthesis to maintain serum protein levels. However, albumin, a small protein (66 kDa), gets filtered through the glomerular basement membrane easily. Therefore, its levels usually remain normal or elevated in nephrotic syndrome, as the body compensates for the loss of larger proteins like transferrin (70 kDa), haptoglobin (24 kDa), and immunoglobulins (150-200 kDa).

**Why Each Wrong Option is Incorrect:**

A. Albumin: As mentioned before, albumin levels usually remain normal or elevated due to increased synthesis to compensate for protein loss.

B. Immunoglobulins: These are large proteins (150-200 kDa) and are also lost in nephrotic syndrome due to proteinuria. The body cannot compensate for the loss of immunoglobulins, leading to their reduction.

C. Transferrin: Similar to albumin, transferrin (70 kDa) levels will be reduced due to increased loss in nephrotic syndrome.

D. Haptoglobin: This protein (24 kDa) also gets filtered and lost in nephrotic syndrome, contributing to its reduction in serum levels.

**Clinical Pearl:** The preservation of albumin levels in nephrotic syndrome is due to increased synthesis, which is crucial as it helps maintain osmotic pressure and maintains vascular tone. This is in contrast to conditions like hyperlipidemia, where elevated lipid levels are seen due to reduced clearance or increased synthesis and lipoprotein lipase activity.

**Correct Answer Explanation:** In nephrotic syndrome, the correct answer is **D** haptoglobin (24 kDa), as it is a protein of a similar size to albumin (66 kDa) and gets filtered through the glomerular basement membrane along with other larger proteins like immunoglobulins and transferrin. The body cannot compensate for the loss of haptoglobin, leading to its reduction in serum levels.