Renal function- basic data for students and residents

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Renal function- basic datafor students and
residents

• Department of Paediatrics
• Section for Pediatric Nephrology
• University Hospital Motol, Prague

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Functions of the kidney

• regulation e.g. homeostasis,
• water, acid/base
• excretion e.g. urea, creatinine
• endocrine e.g. renin,
• erythropoietin,
• 1,25 dihydroxycholecalciferol- conversion only in
  kidney!

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Renal function tests

• detect renal damage
• monitor functional damage
• help determine etiology

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Laboratory tests of renal function

• urine protein
• urine glucose
• hematuria
• osmolality

• glomerular filtration rate (GFR)
• plasma creatinine
• plasma urea
• urine volume
• urine urea
• minerals in urine

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Kidney Function

• A plumbers view

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Kidney basic data

• Urine excreted daily in adults cca 1.5L
• Kidney only ca 1 of total body weight, despite
  it
• The renal blood flow 20 of cardiac output
• Plasma renal flow PRF ca 600 mL/Min./1.73 M2
• Reflects two processes
• Ultrafiltration (GFR) 180 L/day
• Reabsorption gt99 of the amount filtered

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How do you know its broken?

• Decreased urine production
• Clinical symptoms
• Tests

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Where can it break?

• Pre-renal
• Renal (intrarenal)
• Post-renal (obstruction)

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Causes of kidney functional disorders

• Pre-renal e.g. decreased intravascular volum
• Renal e.g. acute tubular necrosis
• Postrenal e.g. ureteral obstruction

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Tests of renal function

• glomerular filtration rateGFR
• plasma creatinine Pcr
• plasma urea-Purea
• urine volume V
• urine urea- Uurea
• cystatin C in plasma?

• urine protein
• urine glucose
• hematuria
• osmolality

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Renal Function Tests- Urine volumes

• Adults
• 1.5 L/24 htypical in health,
• oliguria lt 400 mL,
• anuria lt 100 mL,
• polyuria gt 3000 mL
• Children ca 1.5 ml/Kg of b.w./1 hour!

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Principle of of Clearance

• Some substances when filtered enter the tubules
  are not reabsorbed and so 100 excreted GFR
  (inulin gold standard for GFR, creatinine (but
  this one partially reabsorbed, particularly in
  uremia, then clearance ltGFR
• Some substances are filtered, enter tubules, and
  more of the substance is secreted enters the
  tubules by excretion. ClearancegtGFR
• Some substances are filtered, enter tubules, but
  are completely reabsorbed, so they did not reach
  the final urine (e.g. cystatin C)

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Glomerular filtration rate

• Glomerular filtration major physiologic
  responsibility of kidney, GFR used as index of
  overall excretory function
• Methods
• clearence of inulin, creatinine, EDTA and DTPA
  (both derivates of acetic acid), cystatin C
• GFR Ux x V (Vvolum of urine/ 1 minute or 1
  second)
• P x x clearence of
  substance used

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Glomerular filtration rate

• Also service of nuclear medicine dptm.
• Follow up the inulin clearence, EDTA or DTPA
  clearence labelling the substances with chromium
  or Tcm99
• Where will you catch the activity with
  detectors?
• Never in the kidney or bladder area!!

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Glomerular filtration rate

• GFR in children, value always adapted to the
  BSA!! Ideal BSA in adults is 1.73m2
• Schwartz equation GFR v x 0.808
• 
  Pcr (umol/L)
• How to assess easy if plasma creatinine is OK?
• Pcr max Vcm x 0.61 (v body height in cm

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Creatinine and Urea Plasma Concentration-
hyperbolic correlation
Tendency in individual patients is more important
than the one value, ever test if the hydration is
OK. In patients with CRI always note also the
BSA! Lower limit today not 80 ml/Min. /1.73 m2
but 90 ml/Min./1.73 m2
pCr, pUrea
Normal range-gt
140 mL/min (100)
0 mL/min (0)
GFR 50
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Plasma urea (BUN)

• BUN (blood urea nitrogen)
• Urea product of protein catabolism
• Synthesized by liver, majority excreted by
  kidney, partially reabsorbed in tubuli
• Plasma concentration increases with decreased GFR

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Urea cycle
aspartate
CO2 NH3
Urea Cycle
3 ATP
Urea
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Enzymatic conductivity rate method for measuring
urea
Urea 3H2O
urease
Urease solution
HCO3 2NH4 OH
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Urea in patients with kidney diseases

• Useful test but must be interpreted with great
  care, urea plasma level is more than creatinine
  dependent on protein intake
• Most useful when considered along with
  creatinine
• High in high protein intake, low in severe liver
  dysfunction
• Urea EF may be useful in pts. on diuretics

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Plasma creatinine and renal functions

• Creatine main storage compound of high energy
  phosphate needed for muscle metabolism.
• Creatinine anhydride of creatine!

Creatine
Creatinine
(Waste product)
H2O
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Plasma creatinine vs. GFRnot linear, hyperbolic
correlation!
pCreat
Change within an individual patient is usually
more important than the absolute value
140 mL/min (100)
0 mL/min (0)
GFR
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Jaffe reaction for measuring creatinine, simple,
but better is enzymatic method
Creatinine alkaline picrate solution
Bright orange/red colored complex absorbs light
at 485nm (many interfering substances in
blood Can be minimized using rate method)
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Analytical methods (Cr)

• Normal range Pcr
• Male 0.6-1.2 mg/dL,
• Female 0.5-1.0 mg/dL
• Be careful in children!!
• Remember the max. plasma creatinine value!!

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BUN creatinine ratio

• Pre-renal disorders
• BUNCr ratio gt20
• Renal disorders
• BUN Cr nl but both elevated
• Post-renal

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Osmolality of urine

• Measures urine concentrating ability
• Depends on of particles, not size or charge
• Largely due to ADH (anti-diuretic hormone)
• Can reach maximum of 1200 mOsm/L
• Normal range 300-900mOsm/L, plasma 28510
• prior to collection, fluid intake restricted,
  first void submitted for evaluation
• Measuring using the fact of freezing point
  depression

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Standardized renal concentration capacity test

• 1. Voiding completely at 9 p.m. (WC)
• 2. Desmopressin administration (since 2006 as
  nasal spray). DDAVP is a Czech invention !!
• 3. Collection of urine (9 p.m. 7 a.m.)
• 4. Testing of urine osmolality in this sample
  (not the morning urine only!)
• 5. The lower limit of normal value 950
  mOsm/kg of urine
• 6. Short testing- Desmopressin, collection for
  4 hours only at least 900 mOsm/kg of urine

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Urine dipsticks

• Strip impregnated with reagents for the
  substances in question within a urine sample
• Substance level can be altered in the setting of
  pathology within the urinary tract
• Measured substances
• Modern dipsticks with multiplied zones
• Protein, hemoglobin, glucose, urobilinogen,
  nitrite, leukocytes, specific gravity, and pH
• Should be a tool everywhere on the level of
  primary care!!!