Renal Functions In ChildrenPresentation Transcript
Renal function- basic data for students and residents Department of Paediatrics Section for Pediatric Nephrology University Hospital Motol, Prague
Functions of the kidney
regulation e.g. homeostasis,
excretion e.g. urea, creatinine
endocrine e.g. renin,
1,25 dihydroxycholecalciferol- conversion only in kidney!
Renal function tests
detect renal damage
monitor functional damage
help determine etiology
Laboratory tests of renal function
glomerular filtration rate (GFR)
minerals in urine
A plumbers view
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 M 2
Reflects two processes
Ultrafiltration (GFR): 180 L/day
Reabsorption: >99% of the amount filtered
How do you know it’s broken?
Decreased urine production
Where can it break?
Causes of kidney functional disorders
Pre-renal e.g. decreased intravascular volum
Renal e.g. acute tubular necrosis
Postrenal e.g. ureteral obstruction
Tests of renal function
glomerular filtration rate=GFR
plasma creatinine= P cr
plasma urea-P urea
urine volume= V
urine urea- U urea
cystatin C in plasma?
Renal Function Tests- Urine volumes
1.5 L/24 h typical in health,
oliguria < 400 mL,
anuria < 100 mL,
polyuria > 3000 mL
Children: ca 1.5 ml/Kg of b.w./1 hour!
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 <GFR
Some substances are filtered, enter tubules, and more of the substance is secreted enters the tubules by excretion. Clearance>GFR
Some substances are filtered, enter tubules, but are completely reabsorbed, so they did not reach the final urine (e.g. cystatin C)
Glomerular filtration rate
Glomerular filtration= major physiologic responsibility of kidney, GFR used as index of overall excretory function
clearence of inulin, creatinine, EDTA and DTPA (=both derivates of acetic acid), cystatin C
GFR = U x x V (V=volum of urine/ 1 minute or 1 second)
P x x= clearence of substance used
Glomerular filtration rate
Also service of nuclear medicine dptm.
Follow up the inulin clearence, EDTA or DTPA clearence labelling the substances with chromium or Tc m99
Where will you catch the activity with detectors?
Never in the kidney or bladder area!!
Glomerular filtration rate
GFR in children, value always adapted to the BSA!! Ideal BSA in adults is 1.73m 2
Schwartz equation : GFR= v x 0.808
P cr (umol/L)
How to assess easy if plasma creatinine is OK?
P cr max= V cm x 0.61 (v= body height in cm
Creatinine and Urea Plasma Concentration- hyperbolic correlation GFR 50% pCr, pUrea 140 mL/min (100%) 0 mL/min (0%) 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 m 2 but 90 ml/Min./1.73 m 2 Normal range->
Plasma urea (BUN)
= BUN ( b lood u rea n itrogen)
Urea: product of protein catabolism
Synthesized by liver, majority excreted by kidney, partially reabsorbed in tubuli
Plasma concentration increases with decreased GFR
Urea cycle CO2 NH3 aspartate Urea 3 ATP Urea Cycle
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
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
Plasma creatinine vs. GFR not linear, hyperbolic correlation! GFR [pCreat] 140 mL/min (100%) 0 mL/min (0%) Change within an individual patient is usually more important than the absolute value
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 )
Analytical methods (Cr)
Normal range P cr
Male 0.6-1.2 mg/dL,
Female 0.5-1.0 mg/dL
Be careful in children!!
Remember the max. plasma creatinine value!!
BUN: creatinine ratio
BUN:Cr ratio >20
BUN: Cr nl but both elevated
Osmolality of urine
Measures urine concentrating ability
Depends on # of particles, not size or charge
Largely due to ADH ( a nti- d iuretic h ormone)
Can reach maximum of 1200 mOsm/L
Normal range: 300-900mOsm/L, plasma 285 + 10
prior to collection, fluid intake restricted, first void submitted for evaluation
Measuring using the fact of freezing point depression
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
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
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 !!!