**Core Concept**
Hemolytic Uremic Syndrome (HUS), Post-Streptococcal Glomerulonephritis (PSGN), and IgA Nephropathy (not directly mentioned but related) are kidney diseases that involve immune complex deposition and complement activation. Glomerular Filtration Rate (GFR) is a critical parameter in assessing kidney function.

**Why the Correct Answer is Right**
Option D is correct because PSGN is indeed associated with increased complement levels. PSGN is an immune complex-mediated glomerulonephritis that occurs after streptococcal infection. The disease involves the deposition of immune complexes containing IgG and IgM antibodies against streptococcal antigens in the glomeruli, leading to complement activation and subsequent inflammation. This results in increased levels of complement components such as C3 and C4.

**Why Each Wrong Option is Incorrect**
**Option A:** HSP (Henoch-Schönlein Purpura) is actually associated with IgA deposition, not IgG. IgA is the primary immunoglobulin involved in HSP.
**Option B:** HUS (Hemolytic Uremic Syndrome) typically causes thrombocytopenia due to ADAMTS13 deficiency, but this is not the hallmark feature. Thrombocytopenia is a consequence of the disease, not a primary characteristic.
**Option C:** Inulin clearance is indeed a measure of GFR, but it is not the best or most commonly used method. Inulin is a non-reabsorbed, non-secreted substance that is used as a gold standard for measuring GFR, but other methods like creatinine clearance or cystatin C-based estimates are more practical and widely used.

**Clinical Pearl / High-Yield Fact**
When evaluating kidney diseases, remember the classic "Tobacco Dandelion" association: PSGN is associated with increased complement levels, whereas IgA Nephropathy and HUS are not. This association can help you differentiate between these conditions.

**Correct Answer:** D. PSGN is associated with increased complement.