Proteinuria and Polyuria (Grin) Flashcards
What are the 3 layers of the glomerular barrier?
- fenestrated capillary endothelium (keeps out cells)
- basement membrane (keeps out large proteins)
- podocytes (keeps out large proteins)
What gets through the glomerular filtration barrier?
low molecular weight proteins (beta 2 macroglobulin, light chains) but are REABSORBED in proximal tubules and small solutes and molecules (Na, K, glucose)
Normal daily protein excretion
low molecular weight proteins (ex. Tamm-Horsfall proteins)
Normal limits:
protein <150 mg/day
albumin <30 mg/day
Glomerular proteinuria
damaged glomerular filtration barrier (podocytes and basement membrane) leads to albuminuria
Overflow proteinuria
Filtered low-molecular-weight protein load>reabsorptive capacity of the kidney (multiple myeloma - lots of light chains)
Tubulointerstitial proteinuria
Tubular damage leads to impaired reabsorption of low molecular weight proteins (ex. Acute tubular necrosis)
Orthostatic proteinuria
increased urine protein excretion in the upright position but normal protein excretion in the supine position. typically seen in children. Urinalysis is positive when child is upright, then repeat and normal.
Pros and cons of a urinalysis
Pros: cheap and easy
Cons: only detects albumin when there is a lot present (>300 mg) low sensitivity.
Pros and cons of a spot urine albumin/creatinine ratio
Pros: can detect small amounts of albumin (unlike a urinalysis) - useful in early diabetic nephropathy
Cons: only detects albumin; not good for multiple myeloma
Pros and cons of a spot urine protein/creatinine ratio
Pros: detects all proteins (unlike a urinalysis and spot urine albumin/creatinine ratio) -good for multiple myeloma
Cons: not that good for diabetic nephropathy
What is the current gold standard for measuring proteinuria?
a 24 hour urine protein
pros: gold standard
cons: inconvenient
Pros and cons of a 24 hour urine protein test
pros: gold standard
cons: inconvenient
What test is needed in the case of suspected multiple myeloma?
Need spot urine protein/creatinine ratio to detect light chain proteinuria
Nephrotic syndrome pathophysiology
damaged glomerular filtration barrier allows plasma proteins to pass into the nephron tubule. proteinuria >3.5 g/day (albumin and antithrombin III)
What are the two main proteins being excreted in nephrotic syndrome?
- albumin (hypoalbuminemia- low oncotic pressure-edema)
- anti-thrombin III (anticoagulant - thrombotic and thromboembolic complications)
How does nephrotic syndrome lead to edema
- (underfill theory) proteinuria leads to hypoalbuminemia, leads to decreased oncotic pressure; edema
- (overfill theory) decreased renal blood flow leads to RAAS activation, leads to increased Na retention then water retention; edema
What are the 5 major features of nephrotic syndrome?
- Proteinuria >3.5 g/day
- Edema
- Hyperlipidemia (fatty casts, xanthelasmas)
- Hypoalbuminemia
- Hypercoagulability (DVT/PE and renal vein thrombosis)
What are the 5 main causes of nephrotic syndrome?
- Diabetes (most common)
- Minimal change (children)
- Focal Segmental Glomerulosclerosis (FSGS) - HIV/heroin use
- Membranous (idiopathic primary or secondary with Hep.B/C, syphilis, solid tumors, SLE
- Amyloid
Early pathophysiology of diabetic nephropathy
Lots of glucose in the blood causes non-enzymatic glycation. Increases the pressure in the afferent arterioles, increases the GFR, and causes hyperfiltration. Increase pressure in the bowman capsule and tubules and causes damage of the glomerulus.
Note: early stages creatinine and eGFR will be NORMAL
Late pathophysiology of diabetic nephropathy
- adaptive changes will cause a thickened basement membrane
- mesangial expansion
- Kimmelstiel-Wilson nodules
- Disruption of podocytes
Workup for nephrotic syndrome
basic metabolic panel
urinalysis with microscopy
urine albumin/creatinine ratio and urine protein/creatinine ratio
addition labs (HIV, Hep B/C, lipid panel, A1c)
Renal biopsy