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Flashcards in 4 Clinical Evaluation of Renal Function Deck (33):
1

Kidney

  • Roles of the kidney
  • Most important parameter in assessing kidney function & kidney disease progression

  • Roles of the kidney
    • Maintain homeostasis & a constant extracellular environment
      • Excrete metabolic waste
      • Reabsorb & secrete in tubules
      • Concentrate, dilute, & acidify urine
    • Secrete hormones
  • Most important parameter in assessing kidney function & kidney disease progression
    • Glomerular filtration rate (GFR): renal ecretory capacity

2

GFR

  • General
  • Most common methods to estimate GFR
  • Other markers of kidney function

  • General
    • Most important parameter in clinically evalutating kidney funciton
    • Overall index of kidney function
    • = sum of filtration rates in all functioning nephrons
    • Measure of excretory function
    • Used w/ H&P, urinalysis, imaging, & biopsy to evaluate disease etiology
  • Most common methods to estimate GFR
    • Serum creatinine & estimation equations
      • Most common
      • Rely upon creatinine
    • Creatinine clearance
  • Other markers of kidney function
    • Blood urea nitrogen (BUN)
    • Serum cystatin C (only in reserach)

3

Normal GFR

  • How much plasma glomeruli filter
  • GFR depends on...
  • Normal GFR value
  • GFR vs. age
  • GFR is corrected for...
  • Significance of decreased GFR

  • Glomeruli filter ~125 ml/min of plasma
  • GFR depends on age, sex, & body size
  • Normal GFR = 130 ml/min in men & 120 ml/min in women
  • GFR declines ~1% per year above 40yo
  • GFR is corrected for body surface area (important in children)
  • Significance of decreased GFR
    • Acute or chronic kidney disease
    • Level of GFR assesses disease severity
    • Not an exact correlation b/c kidney adapts to nephron loss by compensatory hyperfiltration in remaining normal nephrons

4

Assessing GFR

  • Measured directly vs. estimated
  • Clearance
  • Amt of plasma filtered by glomeruli
  • Substance chosen for clearance measurement in clinical practice
  • Inulin characteristics
  • Measurement of GFR using inulin clearance

  • Measured directly vs. estimated
    • GFR can't be measured directly but can be estimated from clearance of an ideal filtration marker
  • Clearance
    • Volume of plasma cleared entirely of a substane / time
    • Clearance = (U * V) / P
  • Amt of plasma filtered by glomeruli
    • Estimated by the clearance of ideal markers like inulin
  • Substance chosen for clearance measurement in clinical practice
    • Endogenous creatinine
  • Inulin characteristics
    • Neither absorbed nor secreted by renal tubules
    • Freely filterable across glomerular membranes
    • Not metabolized or produced by kidneys
  • Measurement of GFR using inulin clearance
    • GFR is measured by determining plasma conc & excretion of inulin
    • Amt of inulin excreted = amt filtered
    • Inulin clearance determines amt of plasma filtered by glomreuli (GFR)

5

Assessing GFR w/ inulin clearance

  • Filterability of inulin
  • Equation derivation
  • Equation
  • How Cin is measured
  • Criteria for the clerance of a substance to equal GFR

  • Inulin is freely filterable
    • Amt excreted = amt filtered
    • Conc in filtrate = conc in plasma
  • Equation derivation
    • Filtered amt of inulin = GFR * plasma inulin conc
    • Excreted amt of inulin = urine inulin conc * urine volume
      • Volume units: L / min
    • Filtered amt of inulin = excreted amt of inulin
    • GFR * plasma inulin conc = urine inulin conc * urine volume
  • Equation
    • GFR = [urine inulin conc (Uin) * urine volume (V)] / plasma inulin conc (Pin)
    • GFR = inulin clearance (Cin)
  • How Cin is measured
    • Infuse inulin IV to achieve steady state blood level
    • Measure plasma inulin, urine inulin, & urine volume simultaneously
  • Criteria for the clerance of a substance to equal GFR
    • Substance must be freely filterable at the glomerulus
    • Substance can/t be secreted or reabsorbed in tubules
    • Substance must be in steady state concs in the blood w/ no extrarenal route of excretion

6

Measurement of GFR in clinical practice

  • Inulin vs. creatinine
  • Creatinine characteristics
  • Methods to assess GFR using creatinine

  • Inulin vs. creatinine: in clinical practice...
    • Not practical to use inulin infusion to calc Cin to assess GFR
    • Assess GFR w/ endogenous creatinine
  • Creatinine characteristics
    • Endogenously produced from the metabolism of creatine & phosphocreatine in skeletal muscle
    • Excreted by kidneys
    • Freely filtered across the glomerulus
    • Neither reabsorbed nor metabolized by the kidney
    • Amt filtered = amt excreted when renal function is stable (steady state)
  • Methods to assess GFR using creatinine
    • Calc GFR w/ creatinine clearance
    • Measure serum creatinine
    • Estimate equations using serum creatinine to estimate GFR

7

Steady state

  • Achieved when...
  • Creatinine in steady state

  • Achieved when...
    • Ingested amt + produced amt = excreted amt + consumed amt
  • Creatinine in steady state
    • Filtered creatinine = GFR * serum creatinine conc (Pcr)
    • Excreted creatinine = urine creatinine conc (Ucr) * urine flow rate (V)
      • Constant in absence of acute kidney failure b/c muscle mass remains relatively constant
      • V units: L / min
    • Filtered creatinine = excreted creatinine
  • Take-home about steady state
    • Methods that evaluate GFR (Cr clearance, estimatoin equations) can only be used when Pcr is stable (in steady state), as in pts w/ CKD or stable normal Cr

8

Measurement of creatinine clearance

  • Equation derivation
  • Equation
  • Technique

  • Equation derivation
    • Amt excreted = amt filtered
    • Creatinine is freely filterable so filtrate conc = plasma conc in steady state
    • Filtered Cr = GFR * plasma Cr conc (Pcr)
    • Excreted Cr = urine Cr (Ucr) * urine volume (V)
    • Filtered Cr = excreted Cr
    • CrCl * Pcr = Ucr * V
  • Equation
    • CrCl = GFR = (Ucr * V) / Pcr
    • Units: ml / min
  • Technique
    • 24 hr urine collection
    • Measure Ucr & Pcr
    • Normalized to BSA of 1.73 m2 (esp for children)

9

Example

  • 60 kg women
  • Pcr = 1.2 mg/dL
  • Ucr = 100 mg/dL
  • V = 1.2 L/day
  • Calculate CrCl

  • V
    • = 1.2 L/day
    • = 1.2 L/day * 1000 ml/L * 1/1440 day/min
    • = 0.83 ml/min
  • CrCl
    • = (Ucr * V) / Pcr
    • = (100 mg/dL * 0.83 ml/min) / 1.2 mg/dL
    • = 70 ml/min
  • CrCl = 70 ml/min

10

Limitations of creatinine clearance

  • (1)
  • How (1) is checked
  • Muscle mass in dif pt populations
  • (2)

  • (1) Incomplete urine collection
    • Difficult to obtain a complete 24 hr urine, esp in children
      • Pts forget, collect too much, etc.
    • Impossible to obtain in pts w/ incontinence or diarrhea
  • Adequacy of a 24 hr urine collection is checked by comparing the measured amt of Cr excretion to the expected amt based on weight, gender, & age
    • Women: 15-25 mg/kg/d
    • Men: 20-30 mg/kg/day
    • Elderly (muscle wasting): 10 mg/kg/d
    • Children: 14.7 + (0.45 * age) mg/kg/d
  • Muscle mass in dif pt populations
    • Muscle mass & Cr production/excretion decreases w/ age > 40yo
    • Muslce mass decreases in pts who are bed-ridden, physically inactive, amputed, or on chronic corticosteroids
  • (2) Increasing Cr secretion
    • Decrease GFR --> increase Pcr + enhance tubular secretion
    • Advanced CKD: Cr excreted > Cr filtered --> overestimate GFR

11

Measurement of serum creatinine

  • Cr characteristics
  • GFR vs. Pcr
  • Pcr vs. kidney function
  • Normal Pcr
  • Pcr is affected by...

  • Cr characteristics
    • Endogenously produced from the metabolism of Cr in skeletal muscle
    • Excreted by kidneys
    • Freely filtered across the glomerulus
    • Neither reabsorbed nor metabolized by the kidney
  • GFR vs. Pcr
    • GFR = CrCl = (Ucr * V) / Pcr
    • Decrease GFR --> increase Pcr curvilinearly
  • Pcr vs. kidney function
    • Higher Pcr --> worse kidney function
  • Normal Pcr
    • Adult: 0.6 - 1.2 mg/dl
    • Children: lower
  • Pcr is affected by both Cr production & clearance
    • Muscle mass
    • Diet
    • Creatine supplements
    • Malnutrition
    • Amputations

12

Limitations of serum Cr measurement

  • Cr production differs b/n pts depending on muscle mass
    • More muscle mass --> higher Cr
    • Less muscle mass --> lower Cr
    • Amputation, muscle wasting, malnutrition --> low muscle mass --> Pcr appear normal but could represent low GFR
  • Glomerular injury may not initially change GFR or Pcr
    • If this is suspected, look for other signs of kidney disease (ex. protein or blood in urine, abnormal renal imaging)

13

Estimation equations based on Pcr

  • Why used
  • Cockroft-Gault formula
  • MDRD formula
  • Ex. 23yo white man, 80kg, Cr 1.2 mg/dl

  • Why used
    • Limitations of Pcr due to variatoins in muscle mass
    • Alternatives to 24 hr urine collection
    • Equations take into account variables like age, sex, race, & body size (predictors of muscle mass)
  • Cockroft-Gault formula
    • GFR = [ (140 - age) * (weight in kg) ] / (72 * PCr)
    • For older drug dosing​ guidelines
    • Based on demographics, serum Cr, & lean body weight
    • Multiply by 0.85 for women b/c they have less muscle mass than men
    • Obese pts: weight can over-estimate Cr cleraance, so use lean body weight
  • MDRD (modificaiton of diet in renal disease) formula
    • Most commonly used in clinical practice
    • Effect of dietery protein restriction & BP control on renal disease progression --> equation that predicts GFR from Pcr
  • Ex. 23yo white man, 80kg, Cr 1.2 mg/dl
    • GFR = 80 ml/min

14

Limitations of estimation equations

  • MDRD
  • Cockcroft-Gault
  • Validation in clinical populations
  • Newer methods proposed but not widely used

  • MDRD
    • Tends to underestimate GFR when r is normal or near-normal
    • Why labs report GFR > 60 ml/min when it's expected to be close to nromal (80 ml/min)
  • Cockcroft-Gault
    • Tends to overestimate GFR due to tubular secretion
  • Validation in clinical populations: formulas haven't been validated in...
    • Children
    • Pregnant women
      Certain ethnic groups
    • Pts w/ unusual muscle mass, body habitus, & weight
  • Newer methods proposed but not widely used
    • CKD-EPI
    • Blood test Cystatin C

15

Example

  • 23yo female, 55 kg, 24 hr urine collection
  • V = 2000 ml / 24 hr
  • Ucr = 50 mg/dl
  • Pcr = 0.6 mg/dl

 

  • CrCl?
  • Is kidney function normal?

  • CrCl = (50 mg/dl * 2000 ml / 1440 min) / 0.6 mg/dl = 115 ml/min
  • Normal renal function
    • Normal = 110 ml/min

16

Example

  • 23yo female, 55 kg, 24 hr urine collection
  • V = 2000 ml / 24 hr
  • Ucr = 50 mg/dl
  • Pcr = 1.2 mg/dl

 

  • CrCl?
  • Is kidney function normal?

  • CrCl = (50 mg/dl * 2000 ml / 1440 min) / 1.2 mg/dl = 58 ml/min
  • Moderate decrease in kidney function
    • Normal = 110 ml/min
    • Even though lab reports Pcr of 1.2 mg/dl as normal, level doesn't represent normal kidny function

17

Importance of adequate urine collection

  • Ex. if 23yo woman collects urine for 24 hr but misses several voids
  • Inadequate & incomplete collection
  • Regardless of chronic changes in renal function, Cr excretion...

  • Ex. if 23yo woman collects urine for 24 hr but misses several voids
    • Measured Cr excretion = 500 mg/d
    • Expected Cr excretion = 55 kg * 20 mg/kg = 1100 mg/d
  • Inadequate & incomplete collection
    • Gives false determination of GFR
  • Regardless of chronic changes in renal function, Cr excretion...
    • Is relatively stable over time unless muscle mass changes
    • Decrease GFR --> decrease Cr filtration & excretion --> increase Pcr --> brings total Cr filtration back to normal --> re-establishes balance b/n produciton & excretoin (steady state)

18

Example

  • 23yo 80 kg man w/ more muscle mass than a woman
  • Pcr = 1.2 mg/dl
  • Ucr = 110 mg/dl (compared to a woman: 50 mg/dl)
  • V = 2000 ml / 1440 min

 

  • CrCl?
  • Is kidney function normal?

  • CrCl = (110 mg/dl * 2000 ml / 1440 min) / 1.2 mg/dl = 126 ml/min
  • Normal kidney function
    • Ucr is a reflection of muscle mass (muscle breakdown product)
      • More muscle --> more urinary Cr
    • "Normal" Pcr range of 0.6 - 1.2 mg/dl only reflects normal GFR in light of pt muscle mass

19

Summary of measurement of GFR in clinical practice

  • Cr clearance
    • Method
    • Cons
  • Pcr
    • Method
    • Pros
    • Cons
  • Estimated GFR using MDRD
    • Method
    • Pros
  • Estimated GFR using Cockcroft-Gault
    • Method
    • Pros
    • Cons

  • Cr clearance
    • Method
      • Urine 24 hr collection of Cr w/ simulatneous Pcr measurement
    • Cons
      • Urine collection can be unreliable
        • Inadequate or over-collection --> false results
      • Can overestimate GFR secondary to increased creatinine secretion in advanced CKD
  • Pcr
    • Method
      • Simple blood draw
    • Pros
      • Easy to obtain
    • Cons
      • Varies w/ muscle mass & is inaccurate in extreme muscle mass
      • Affected by some drugs
  • Estimated GFR using MDRD
    • Method
      • Simple blood draw
    • Pros
      • Avoids urine 24 hr collection
      • Better estimation of GFR than Pcr alone
      • Commonly reported on clinical lab results
  • Estimated GFR using Cockcroft-Gault
    • Method
      • Simple blood draw
    • Pros
      • Avoids urine 24 hr collection
      • Commonly used in prescribing info for dose adjustments
    • Cons
      • Tends to over-estimate GFR

20

Blood urea nitrogen (BUN)

  • Normal values
  • Use
  • BUN vs. Cr for measuring GFR
  • BUN assesses...
  • Azotemia

  • Normal values
    • 7-21 mg/dl
  • Use
    • Marker of kidney function
    • Kidney failure --> increased BUN
  • BUN vs. Cr for measuring GFR
    • BUN is a worse marker b/c it's also dependent on...
      • Protein intake
        • Increase intake --> increase BUN
      • Catabolism
        • Increase catabolism --> increase BUN
      • Liver function
        • Cirrhosis --> decrease BUN
      • Volume status
        • Volume depletion --> low urine flow rates --> increase urea reabsorption along renal tubules
    • Urea clearance = 60% of Cr or inulin clearance
  • BUN assesses...
    • GFR
    • Protein intake
    • Presence of catabolism
    • Volume status
    • Renal perfusion
  • Azotemia
    • Elevation of BUN & Pcr

21

Acute kidney injury (AKI)

  • AKI definition
  • GFR in AKI
  • Cr in AKI
  • CrCl in AKI

  • AKI definition
    • Loss of renal function over hours to days
    • Azotemia: retention of nitrogenous waste broducts in blood
      • Increased BUN & Pcr
  • GFR in AKI: decreased due to...
    • Decreased Cr excretion
    • Increased Pcr & BUN
    • Pt not in steady state
  • Cr in AKI: decreased
    • Production stays constant
    • Pcr increases due to muscle mass & muscle break down (1 mg/dl / day)
  • CrCl in AKI: not used
    • 24 hr urine collection not used
      • CrCl isn't a reflection of GFR b/c the pt isn't in steady state
      • Pcr is increasing daily, which is a variable in CrCl/GFR estimation
    • Formulas to determine CrCl also don't apply

22

Example

  • 22yo 80kg male involved in a car accident
  • --> ICu w/ HoTN & multiple injuries
  • Urine output = 10 cc / 4 hr
  • Pcr = 1.2 mg/dl
  • Urine exam: tubular cells & granular casts
  • BUN & Cr: increase daily, keep ~10-15 : 1 ratio consistent

 

  • CrCl?
  • Kidney function assessment

  • Can't calculate CrCl / GFR b/c not in steady state
    • Increasing BUN & Pcr --> formulas for CrCl aren't applicable
  • Kidney function assessment
    • Urine output of 10 cc / 4 hr = absence of urine output = kidney failure
    • BUN : Cr :: 10-15 : 1 --> intrinsic renal disease
      • Acute tubular necrosis from low BP secondary to bleeding from the accident
      • Helps determine locaiton of kidney problem (pre-kidney, intrinsic, or obstruction)

23

Tools to evaluate kidney abnormalities

  • H&P
  • Assessment of GFR
    • Chronic renal failure: calc GFR from Pcr if chronic
    • Acute renal failure: calc pattern of increase in BUN & Cr 
  • Urinalysis
    • Include urine sediment
  • Imaging
  • Kidney biopsy (sometimes)

24

Urinalysis: specific gravity

  • Specific gravity
    • Definition
    • Range
    • Increased by...
    • Determined by...
    • Dependent on...
  • Osmolality
    • Dependent on...
  • Specific gravity vs. osmolality
    • Dilute urine
    • Concentrated urine

  • Specific gravity
    • Weight of urine compared to distilled water
    • Range: 50-1200 mOsm/kg
    • Increased by glucosuria & radiographic contrast excreted in urine
    • Determined by hydrometer, refractometer, & dipstick
    • Dependent on the number, size, & density of particles in urine
  • Osmolality
    • Dependent only on the number of particles in urine
  • Specific gravity vs. osmolality: roughly correlate
    • Dilute urine: osmolality = 50 mOsm/kg --> specific gravity = 1.001
    • Concentrated urine: osmolality = 800 mOsm/kg --> specific gravity = 1.02

25

Urinalysis: chemical composition by dipstick

  • Urine pH
    • Range
    • Useful in evaluating...
    • UTIs
  • Blood
    • Descrimination
    • Location
    • Problem indicated
  • Glucose
    • Normally
    • Some renal diseases
  • Ketones
    • May be present w/...
  • Urobilinogen
    • Produced in...
    • Some...
    • Obstructive jaundice
    • Non-obstructive jaundice
  • Bilirubin
    • Urine obtains...
  • Nitrite
    • Screening test
    • Won't detect...
    • False negatives
  • Leukocytes
    • Threshold
    • False negatives

  • Urine pH
    • Range: 4.5 - 8.0
    • Useful in evaluating pts w/ renal stone disease
      • Uric acid stones may be associated w/ a low urine pH
      • Ca phosphate stones may be associated w/ a high urine pH
    • UTIs w/ urea splitting organisms --> high (alkaline) pH
  • Blood
    • Doesn't discriminate b/n RBCs, hemoglobinuria, & myoglobinuria
      • Microscopic exam determines if RBCs are present
    • May be from any site (kidney, ureter, bladder, urethra, prostate/vagina)
    • RBCs + proteinuria --> intrinsic renal problem
  • Glucose
    • Normally: all glucose is freely filtered at the glomerulus & reabsorbed
    • Some renal diseases: low glucose absorption threshold --> glucosuria at normal serum glucose levels
  • Ketones
    • May be present w/ diabetic ketoacidosis or starvation
  • Urobilinogen
    • Produced in gut from metabolized bilirubin
    • Some is reabsorbed & excreted in urine
    • Obstructive jaundice: bilirubin doesn't reach gut --> decreased urobilinogen
    • Non-obstructive jaundice: increased urobilinogen
  • Bilirubin
    • Urine only obtains unconjugated bilirubin
  • Nitrite
    • Screening test for gram(-) bacteria that convert urinary nitrate --> nitrite
    • Won't detect infections due to enterococcus or non-nitrite-producing organisms
    • Ascorbate --> false negatives
  • Leukocytes
    • Threshold: 5-15 WBC/HPF
    • False negatives: glycosuria, high specific gravity, cephalexin, tetracycline therapy

26

Urinalysis: chemical composition by dipstick: proteinuria

  • Normally
  • Protein confirmation & quantificaiton
  • Estimating daily protein excretion
  • Abnormal proteinuria may result from...
  • Macroalbuminuria
  • Microalbuminuria
  • Nephrotic range proteinuria

  • Normally
    • No protein detected (< 100 mg/d)
    • High amts --> glomerular (not tubular) disease
  • Protein confirmation & quantificaiton
    • Protein presence confirmed by adding 20% sulfasalicyclic acid to urine --> precipitates protein --> makes urine cloudy
    • Protein amt quanitifed w/ 24 hr urine collection + Cr measurement
  • Estimating daily protein excretion
    • Estimate from urine albumin or ptorein & creatinine in a spot urine
    • Albumin or protein conc / Pcr = protein : Cr ratio to estimate 24 hr protein excretion
  • Abnormal proteinuria may result from...
    • Leaking of protein through an abnromal BM (primarily albumin)
    • Leaking of protein from tubules
      • Uncommon, seen in Blakan nephropahty & other tubulointerstitial nephritis
    • Overlow protein
      • In multiple myeloma (Bence-Jones protein) or other disorders w/ increased Ig production
  • Macroalbuminuria
    • Albuminuria > 300 mg/d
    • Detected by dipstick
  • Microalbuminuria
    • Albuminuria 30 - 300 mg/d
    • Measured to detect early diabetic nephropathy
  • Nephrotic range proteinuria
    • > 3 g/d of proteinuria
    • Seen in glomerulonephritis

27

Microscopic examination of urine

  • Use
  • Bland sediment
  • Acute tubular necrosis sediment
  • Nephritic sediment
  • Nephrotic sediment
  • Pyelonpehritis & acute interstitial nephritis
  • Chronic renal failure
  • Telescoped urine

  • Use
    • Assessing dif possible causes of renal failure
    • Diagnosing UTIs & hematuria
  • Bland sediment
    • Normal urine w/ few cells/casts
    • Only casts that may be seen: hyaline
      • May form in increased numbers w/ fever & exercise
    • Pre-renal azotemia or obstruction: few formed elements in urine
  • Acute tubular necrosis sediment
    • Most common cause of acute renal failure
    • Has tubular cells, granular debris, & pigmented granulra casts
  • Nephritic sediment
    • Has dysmorphic RBCs & acanthocytes w/ granular & RBC casts
      • RBC casts indicate glomerular hematuria
    • Present in proliferative glomerulonephritis & renal vasculitis
  • Nephrotic sediment
    • Has 4+ protein, fatty casts, & oval fat bodies (lipid filled cells)
    • Seen in...
      • Glomerulonephritis w/ nephrotic range proteinuria
      • Non-proliferative glomerulonephritis w/ heavy proteinuria
  • Pyelonpehritis & acute interstitial nephritis
    • Has many WBCs & WBC casts
    • (+) culture for pyelonephritis (>105 organisms) but not acute interstitial nephritis
  • Chronic renal failure
    • Has broad casts w/ dilated tubules in functioning nephrons
  • Telescoped urine
    • Has chronicity (broad casts) & more acute disease (granular casts & RBC casts)
    • Characteristic bu tnot specific for rapidly progressive glomerulonephritis

28

Crystals found in urine

  • Calcium oxalate
  • Uric acid crystals
  • Cystine crystals
  • Triple (magnesium ammonium) phosphate crystals
  • Calcium carbonate crystals

  • Calcium oxalate
    • Found in acid urine
    • May occur w/o disease
    • Look like envelopes
    • Ethylene glycol overdose --> increased Ca oxalate crystalluria
  • Uric acid crystals
    • Found in acid urine
    • Varied appearance
  • Cystine crystals
    • Found in acid urine
    • Hexagons
    • Always pathologic
    • Presence confirmed by nitroprusside test
  • Triple (magnesium ammonium) phosphate crystals
    • Found in alkaline urine
    • Associated w/ urea spliting bacteruria & infection
    • Look like coffins
  • Calcium carbonate crystals
    • Found in alkaline urine
    • Granular masses or dumbbells

29

Imaging techniques

  • Renal ultrasound
  • Computer assisted tomography & magnetic resonance imaging
  • Renal arteriogram
  • Intravenous pyelogram
  • Radioisotopic imaging

  • Renal ultrasound
    • Good for renal size, renal masses, echogenicity, renal cysts, & obstruction
    • Safe
    • Doesn't involve IV dye
    • Doppler imaging of renal vessels can assess renal artery stenosis or thrombosis
  • Computer assisted tomography & magnetic resonance imaging
    • Evaluate renal masses & copmlex cyst & renal blood vessels
    • Seldom first imaging study ordered
  • Renal arteriogram
    • Used to confirm renal artery stenosis or complete the evaluation of a renal tumor
    • Last step in evaluating a potential living related renal transplant donor
  • Intravenous pyelogram
    • Not commonly used
  • Radioisotopic imaging
    • Evaluates the function of the kidney
    • useful in diagnosing renal artery stenosis when enalaprilat is used

30

Example

  • 40yo 50kg woman w/ Lupus
  • H: swelling of legs, fatigue
  • P: lower extremity edema
  • Urinalysis: 4+ protein & 2+ blood (normal is 0)
  • Ucr = 100 mg/dl, Pcr = 1 mg/dl, BUN = 10 mg/dl
  • 24 hr urine collection: 5 g/day proteinuria, 1000 mg/day total urinary Cr

 

  • CrCl
  • Kidney function

  • CrCl
    • (100 mg/dl * 1000 mg / 1440 min) / 1 mg/dl = 69 ml/min
  • Kidney funciton: abnormal
    • Decreased GFR --> early CKD
    • Heavy protein leak
    • Blood in urine --> inflammation

31

Example

  • 40yo 72kg male
  • Gross hematuria
  • FH: father died of kidney failure
  • P: proteuberant abdomen, BP = 150/100
  • Lab: Pcr = 4 mg/dl, BUN = 40 mg/dl
  • Urinalysis: 4+ blood, trace protein
  • Ultrasound: enlarged kidneys

 

  • CrCl
  • Kidney function

  • CrCl
    • CG: [(140 - 40) * 72] / (4 * 72) = 25 ml/min
  • Kidney function: abnormal
    • Decreased GFR + FH kidney disease + enlarged kidneys --> AD polycystic kidney disease

32

Example

  • 70yo 80 kg man
  • Severe HTN
  • H: smoker, high cholesterol, 3 anti-HTN meds
  • P: BP = 180/120, fundi w/ HTN blood vessel changes, S4 gallop, 1+ ankle edema
  • Lab: Pcr = 2 mg/dl, BUN = 50 mg/dl
  • Urinalysis: no protein, no blood
  • Angiogram: no blood flow to one kidney, severe stenosis of renal artery on other kidney

 

  • CrCl
  • Kidney function

  • CrCl
    • C-G formula: [(140 - 70) * 80] / (2 * 72) = 41 ml/min
  • Kidney function: abnormal
    • Moderately decreased GFR + no blood flow + stenosis --> renovascular disease

33

GFR evaluation summary

  • BUN
    • CKD
    • AKI
  • Pcr
    • CKD
    • AKI
  • 24 hr urine CrCl
    • CKD
    • AKI
  • Cockroft-Gault formula
    • CKD
    • AKI
  • MDRD formula
    • CKD
    • AKI

  • BUN
    • CKD: +
    • AKI: +
  • Pcr
    • CKD: ++
    • AKI: ++
  • 24 hr urine CrCl
    • CKD: +++
    • AKI: no
  • Cockroft-Gault formula
    • CKD: +++
    • AKI: no
  • MDRD formula
    • CKD: +++
    • AKI: no