Renal Function Flashcards
Why does the BUN always slightly underestimate the GFR?
Urea is freely filtered and PARTIALLY REABSORBED by the nephron
What causes increased urea reabsorption?
Hypovolemia
-BUN underestimates GFR even more in hypovolemic states
What is Azotemia?
Increase in BUN
A High BUN and its toxic effects is called what?
Uremia
Why does creatinine slightly overestimate BUN?
- Passes freely through the glomerulus
- Small amount is secreted by the tubules
- Quantity of tubular secretion increases with increasing serum creatinine concentration
What is a normal BUN/creatinine ratio?
10:1
What causes in increase in BUN/creatinine ratio?
Renal hypoperfusion (hypovolemia, hypotension, etc.) -Ratio may be >20:1
*Prerenal Azotemia
What is the BUN/creatinine ratio in intrarenal causes of renal failure?
Near Normal ratio (10:1)
What does the kidney do with Cystatin C?
- Freely filtered by glomerulus
- Reabsorbed by the proximal tubule (completely)
Cystatin C vs. serum creatinine
Cystatin C is as a good for estimating GFR
-Less dependent on age, sex, or muscle mass
Cystatin C is a strong predictor of what?
Cardiovascular mortality in patients with chronic renal disease
What is a normal proteinuria?
does not exceed 150 mg/day
*mainly Tamm-Horsfall protein
Significant proteinuria is defined as what?
> 300 mg/day
How do you assess proteinuria?
24 hour urine collection
The urine dipstick result (1+ to 3+) is semiquantitative and most sensitive to what?
Albumin
*not sensitive enough to detect microalbuminuria
The presence of what proteins in urine suggest tubular dysfunction?
- B2-microglobulin
- Lysozyme
*These are freely filtered by the glomerulus and then completely reabsorbed by the normally functioning Proximal Convoluted Tubule (PCT)
The current recommendation of the National Kidney foundation is annual testing for those at high risk for CKD, who qualifies for this?
- Diabetes Mellitus
- Hypertension
- Family history of renal disease
What is the recommended screening tests for high risk for CKD?
- eGFR
- Microalbuminuria screen
What is the microalbuminuria screen?
Urine albumin:Creatinie ratio
Chronic Kidney disease is defined by what?
- GFR <60 mL/min/1.73m^2 of body surface area
- Albuminuria for 3 or more consecutive months
Acute Renal Failure - Prerenal vs. Intrarenal:
-Causes
- Prerenal - Hypoperfusion
- Intrarenal - Injury to nephron (glomeruli, tubules, vessels, or interstitium)
Acute Renal Failure - Prerenal vs. Intrarenal:
-BUN:Creatinine ratio
- Prerenal - >20:1
- Intrarenal - <20:1
Acute Renal Failure - Prerenal vs. Intrarenal:
-Urine specific gravitity
- Prerenal - High (>1.020)
- Intrarenal - Low (<1.010)
Acute Renal Failure - Prerenal vs. Intrarenal:
-Urine Osmolarity
- Prerenal - High (>500 mOsm/kg)
- Intrarenal - Low (300-500 mOsm/kg)
Acute Renal Failure - Prerenal vs. Intrarenal:
-FE Na (fractional excretion of Sodium)
- Prerenal - <1%
- Intrarenal - >1%
Acute Renal Failure - Prerenal vs. Intrarenal:
-FE urea (fractional excretion of Urea)
- Prerenal - <35%
- Intrarenal - >35%
Acute Renal Failure - Postrenal:
- Causes
- BUN:Cr ratio
Bilateral obstruction of the renal collecting system
- Bladder outlet obstruction (prostatism)
- Ureteral obstruction (tumor, etc.)
BUN:Cr ratio often ELEVATED
What is the most common cause of Intrarenal Acute Renal Failure?
Acute tubular necrosis (ATN)
What are the most common causes of ATN
- Ischemia
- Nephrotoxins
In intrarenal ARF, urine may show “active” sediment:
-Glomerulonephritis
- RBCs and RBC casts
- Granular casts
Acute Renal Failure - Prerenal vs. Intrarenal:
-Acute Tubular Necrosis
Granular casts
Acute Renal Failure - Prerenal vs. Intrarenal:
-Interstitial nephritis
Granular casts
Acute Renal Failure - Prerenal vs. Intrarenal:
-Pyelonephritis
WBC casts
Acute Renal Failure - Prerenal vs. Intrarenal:
-Acute Allergic Interstitial nephritis
Eosinophils
