A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 22-year-old man comes to the emergency department because of several episodes of blood in his urine and decreased urine output for 5 days. His blood pressure is 158/94 mm Hg. Examination shows bilateral lower extremity edema. Urinalysis shows 3+ protein and red blood cell casts. Mass spectrometry analysis of the urinary protein detects albumin, transferrin, and IgG. Which of the following best describes this type of proteinuria?
-
A
TubularIncorrect. Tubular proteinuria is dominated by low-molecular-weight proteins (beta-2 microglobulin) reflecting impaired tubular reabsorption — not albumin/transferrin/IgG.
-
B
OverflowIncorrect. Overflow proteinuria is from a single circulating protein excess (Bence Jones light chains, hemoglobin, myoglobin), not a mix of medium-to-large plasma proteins.
-
C
PostrenalIncorrect. Postrenal proteinuria is small in amount and is typically from urinary tract bleeding or infection, not from a glomerular filter defect.
-
D
Nonselective glomerularCorrect. The presence of multiple medium-to-large plasma proteins (albumin, transferrin, IgG) indicates nonselective glomerular proteinuria from severe glomerular barrier injury.
-
E
Selective glomerularIncorrect. Selective glomerular proteinuria (e.g., minimal change disease) shows ALBUMIN only, sparing larger plasma proteins like IgG; the presence of IgG and transferrin here indicates a NONselective leak through a severely damaged filter.
↑ Tap an answer to reveal the reasoning
Answer: D. A young patient with hematuria, RED BLOOD CELL CASTS, proteinuria, hypertension, edema, and decreased urine output has acute nephritic syndrome from glomerular injury (likely IgA nephropathy or post-streptococcal GN given his age, though the question doesn't specify the cause). The proteinuria question is about the COMPOSITION of the urinary protein.
Mass spectrometry detecting ALBUMIN, TRANSFERRIN, AND IgG indicates NONSELECTIVE GLOMERULAR proteinuria. In SELECTIVE glomerular proteinuria (classic minimal change disease), the glomerular filtration barrier loses its size/charge selectivity only mildly, allowing primarily albumin to leak through. In NONSELECTIVE glomerular proteinuria (most other glomerular diseases — membranous, FSGS, nephritic syndromes), larger proteins like IgG and other immunoglobulins also pass into the urine — indicating more severe glomerular damage.
Key distinctions: TUBULAR proteinuria reflects failure to reabsorb low-molecular-weight proteins (beta-2 microglobulin, retinol-binding protein) and is seen in tubulointerstitial disease — albumin would be minimal. OVERFLOW proteinuria reflects excess of a single circulating protein overwhelming reabsorption, like Bence Jones light chains in multiple myeloma or hemoglobinuria in hemolysis. POSTRENAL proteinuria is from urinary tract bleeding/infection downstream — typically small amounts mixed with blood.
**Why each option:**
**A.** Tubular proteinuria is dominated by low-molecular-weight proteins (beta-2 microglobulin) reflecting impaired tubular reabsorption — not albumin/transferrin/IgG.
**B.** Overflow proteinuria is from a single circulating protein excess (Bence Jones light chains, hemoglobin, myoglobin), not a mix of medium-to-large plasma proteins.
**C.** Postrenal proteinuria is small in amount and is typically from urinary tract bleeding or infection, not from a glomerular filter defect.
**D.** Correct. The presence of multiple medium-to-large plasma proteins (albumin, transferrin, IgG) indicates nonselective glomerular proteinuria from severe glomerular barrier injury.