Renal Physiology
GFR
- How to measure renal function in clinical practice
- Serum creatinine and serum cystatin C are the primary biomarkers used to estimate GFR
- Nonlinear relationship
- Every time GFR halves, the serum creatinine doubles
- PCT meds that decrease creatinine excretion:
- Cimetidine, Trimethoprim, Cobicistat, Dolutegravir, Bictegravir, Rilpivirine
- Non-progressive rise in serum creatinine (0.2-0.3 mg/dL)
- Do not affect GFR
- Do not need to stop unless (hematuria, pyuria, proteinuria increase)
- Could measure Cystatin C
- Cystatin C less affected by age, sex, muscle mass
- BUN
- Affected by protein intake and catabolic rate
- Increases with glucocorticoids, hemorrhage, or trauma
False Creatinine Elevations
- Increased Production (0.5-1.0)
- Menstrual and Diurnal variations, race, and diet (meat)
- Intense Exercise
- Increased meat intake or Creatine Supplements
- Fenofibrates (8-18% change), Rhabdomyolysis
- Corticosteroids (10%)
- Interference
- Antibiotics (Cephalosporins especially cefoxitin and cefazolin)
- Barbiturates, N-acetylcysteine, chemo drugs (Flucytosine)
- Dopamine (-)
- Ketone bodies
- Decreased Tubular Secretion (15%)
- Trimethoprim, Cimetidine, H2 blockers, Ranitidine
- Pyrimethamine, Salicylates, Cobicistat, Calcitriol
Indications for Kidney Biopsy
- Glomerular hematuria
- Severely Increased Albuminuria
- Acute on chronic kidney disease
- Kidney Transplant dysfunction or monitoring