Term
What is the most important parameter in assessing kidney function and the progression of kidney disease?
How is it estimated? |
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Definition
1) Glomerular filtration rate (GFR), the renal excretory capacity.
This can also be thought of as the amount of plasma that is filtered per minute (usually 125 ml/min and 180L per day for males and 100 ml/min for females)
2) Serum Creatine most commonlyused.
- Serum creatinine concentration
- creatinine clearance
- estimation equations based upon serum creatinine
** Also can use blood urea nitrogen or serum cystatin C (research only)** |
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Term
| Why might a patient is severe renal hypoplasia have normal GFR? |
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Definition
| The kidney adopts to a smaller number of nephrons by compensatory hyperfiltration through the remaining nephrons. |
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Term
| How is GFR measured clinically? |
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Definition
| Endogenous creatinine clearance |
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Term
| How can you use inulin filtration as an estimate of GFR? |
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Definition
Although not used in clinical practice, it is a useful example (Inulin is freely filterable, neither secreted nor reabsorbed by tubules and maintained at a steady state concentration in the blood)
1) Filtered amount of inulin= GFR X plasma inulin concentration
2) Excreted inulin= Urine inulin concentration X urine volume
3) Excreted amount= Filtered amount
So...GFR= (Urine inulin X Urine volume)/ (Plasma inulin) |
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Term
| How can you calculate GFR using Creatinine clearance in stable/chronic kidney disease? |
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Definition
Completely filtered by glomeruli and not reabsorbed by tubules.
Creatinine clearance= (Urine creatinine * Urine volume)/ (Plasma creatinine)
Measure over 24h period (in ml/min) and normalize to BSA of 1.73 in children. |
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Term
| What are the limitations of using creatinine clearance to estimate GFR in stable kidneys? |
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Definition
1) Incomplete urine collection
- 24h (what about incontinence)
2) Increasing creatinine secretion in chronic stable kidney disease can result in large overestimations of GFR because excretion is greater than filtered load. |
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Term
| How can you calculate GFR using Serum creatinine in stable/chronic kidney disease? |
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Definition
Normal is 0.6 to 1.2 mg/dl (lower in children)
Since creatinine is freely filtered across the glomerulus and is neither reabsorbed nor metabolized by the kidney, a decrease in GFR leads to an INCREASE in serum creatinine. The HIGHER the serum creatinine, the LOWER the kidney function.
Curvilinear relationship (convex asymptote) |
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Term
| What are the major limitations of using serum creatinine to measure GFR? |
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Definition
1) Production of creatinine differs among individuals depending on muscle mass
2) Glomerular injury may not initially lead to changes in GFR or serum creatinine (look also look for protein or blood in urine). |
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Term
| How can you calculate GFR using estimation equations based on serum creatinine? |
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Definition
Take into account age, sex, race and body size to predict muscle mass and account for individual variations in creatinine production.
1) Cockroft-Gault is baed on demographics, serum creatinine and lean body weight
(140-age) X weight in kg/ (72 X serum creatinine)
**Multiplied by 0.85 for women!**
- can be used to develop drug dosing, but MDRD is used clinically!!
2) MDRD: Dietary protein restriction and BP control on progression of disease
186.3 X (SCr ^ -1.154) X (Age ^-0.203) X (0.742 if female) X (1.21 if black) |
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Term
What are the major limitations of using the MDRD formula to estimate GFR?
What about the Cockcroft-Gault? |
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Definition
1) MDRD underestimates GFR, when creatinine is normal or "near-normal"
2) Cockcroft-Gault overestimates GFR due to tubular secretion. |
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Term
True or False:
"Normal serum creatinine may not represent normal GFR in people with little muscle mass" |
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Definition
True! So beware in small adults and elderly with muscle wasting.
**Also, males have more muscle mass, so are expected to have HIGHer creatinine levels** |
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Term
| Why is Blood urea nitrogen (BUN) a poorer measure of GFR than creatinine? |
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Definition
Generally 60% of creatinine clearance
It depends on.. (AND IS HELPFUL TO ASSESS THEM)
1) Protein intake
2) Catabolism
3) Liver function (cirrosis decreases it)
4) Volume status (low volume causes increased urea reabsorption) |
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Term
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Definition
| Elevation of BUN and serum creatinine |
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Term
| How can you assess kidney function in stable chronic kidney disease? |
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Definition
1) Creatinine clearance
2) Serum creatinine
3) Estimation equations based on serum creatinine. |
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Term
| How can you assess kidney function in acute kidney injury (AKI)? |
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Definition
AKI is
1) Loss of renal function over hours to days
2) Expressed clinically as retention of nitrogenous waste products such as BUN and serum creatinine in blood (azotemia)
THERE IS NO STEADY STATE HERE
The ratio of BUN:Creatinine can help you determine the location of the kidney problem (pre-kidney, intrinsic kidney or obstruction). |
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Term
| What are the essential elements of Urinalysis? |
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Definition
1) SG (weight of urine to distilled water)
2) pH dipstick
3) Glucose
4) Ketones
5) Blood protein
6) Bilirubin
7) Urobilinogen
8) NItrate
9) Leukocytes
10) Microscopy for casts |
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Term
How does Specific Gravity differ from Osmolality?
How can you determine SG? |
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Definition
1) Osmolality depends only on number of particles in urine, while SG also depends upon the size and density of those particles.
**They are correlated as 50mOsm/kg = 1.001 SG**
2a) Hydrometer
2b) Refractometer
2c) Dipstick |
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Term
You collect a dipstick from a patient with kidney stone disease and their urine has a pH of 4.5.
How does this finding help you? |
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Definition
Acidic pH in renal stone disease means they are URIC ACID
Basic pH would have indicated CALCIUM PHOSPHATE
**You also see high urine pH in UTI** |
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Term
You order a dipstick and determine that their is protein in the patient's urine. How can you confirm this result?
A spot urine test reveals albumin levels to be 310 mg/d. What is this called? |
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Definition
1) Add 20% sulfasalicylic acid to ppt it.
2) Collect urine for 24h or measure spot urine for albumin and creatinine and back-calculate.
3) Macroalbuminuria (micro is >30 mg/d but <300 mg/d) |
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Term
| What are 3 causes of abnormal proteinuria? |
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Definition
1) Abnormal BM lets albumin leak through
2) Tubule leakage (Balkan nephropathy RARE)
3) "Overflow" protein in multiple myeloma (Bence-Jones protein) |
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Term
| What do you know if you detect proteinuria and hematuria? |
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Definition
It is an intrinsic kidney problem.
Remember, to determine between myoglobin and hemoglobin, you need a scope. |
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Term
| Why might you detect ketones in a patient's urine? |
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Definition
1) Diabetic ketoacidosis
2) Starvation |
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Term
| How can Urine Urobilinogen levels be useful in the differential diagnosis of jaundice? |
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Definition
Produced in gut from bilirubin metabolism, and then reabsorbed and excreted in urine.
Urine levels tell you about obstruction.
1) In obstructive jaundice, no bilrubin reaches the gut, so urobilinogen is decreased.
2) In non-obstructive jaundice, urinary urobilinogen is increased. |
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Term
On microscopic urine evaluation, what do each of the following mean?
1) Hyaline casts
2) Pigmented granular casts with tubular cells
3) RBCs and RBC and granular casts
4) +4 protein, fatty casts and oval fat bodies
5) WBCs
6) Broad casts
7) Broad casts and granular and RBC casts |
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Definition
1) May increase in fever or exercise, but are usually normal
2) Acute tubular necrosis causing acute renal failure
3) Nephritis (immune complex)- either proliferative glomerulonephritis or renal vasculitis
4) Nephrotic from non-proliferative glomerulonephritis with heavy proteinuria
5) May be Pyelonephritis or Acute interstitial nephritis
6) Chronic renal failure (tubule dilation)
7) "Telescoped urine" (both acute and chronic) in rapidly progressive glomerulonephritis. |
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Term
| What can the presence of granular, RBC and broad casts tell you about the nature of renal disease? |
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Definition
RBC and Granular casts are generally seen in acute disease, while Broad casts are seen in more chronic disease.
BOTH are found in Telescoped urine, in the context of rapidly progressive glomerulonephritis. |
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Term
| What are the major types of crystals found in urine? What do they mean? |
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Definition
1) Calcium oxylate= Acid urine often due to ethylene glycol poisoning
2) Uric acid= Acid urine with varied appearance
3) Cystine- Always pathologic in acid urine (confirmed by nitroprusside test)
4) Triple (magnesium ammonium) phosphate- Alkaline urine and associated with urea splitting bacteruria and infection (coffin-like)
5) Calcium carbonate- Alkaline urine |
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Term
| Which types of crystals are found in acid vs. alkaline urine? |
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Definition
Acid
1) Calcium oxylate (ethylene glycol poison or normal)
2) Uric acid
3) Cystine (confirmed by nitroprusside)
Alkaline
1) Triple (magnesium ammonium) phosphate- Bacteruria "coffins"
2) Calcium phosphate- "Dumbells" |
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Term
Which of the following renal imaging techniques is most commonly used?
1) CAT/MRI
2) IV Pyelogram
3) Renal Ultrasound
4) Renal Arteriogram
5) Radioisotopic imaging |
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Definition
Renal Ultrasound
- Good for size, masses, echogenicity, cysts, and obstruction.
- Safe, without iV dye and can find stenosis with doppler imaging. |
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