Functions of the kidneyFunctions of the kidney
regulation e.g. homeostasis,regulation e.g. homeostasis,
water, acid/basewater, acid/base excretion e.g. urea, creatinineexcretion e.g. urea, creatinine endocrine endocrine e.g.e.g. renin, renin,
erythropoietin, erythropoietin, 1,25 1,25 dihydroxycholecalciferoldihydroxycholecalciferol- - conversion only in kidney! conversion only in kidney!
Renal function testsRenal function tests
Detect renal Detect renal damagedamage
Monitor Monitor functional damagefunctional damage
Help determine Help determine etiologyetiology
Laboratory tests of renal functionLaboratory tests of renal function
glomerular filtration glomerular filtration raterate (GFR) (GFR)
plasma creatinineplasma creatinine plasma ureaplasma urea urine volumeurine volume urine ureaurine urea minerals in urineminerals in urine
urine proteinurine protein urine glucoseurine glucose hematuriahematuria osmolalityosmolality
Kidney FunctionKidney Function
A plumbers viewA plumbers view
Filter
Processor
InputArterial
OutputVenous
OutputUrine
Kidney – basic dataKidney – basic data
UUrine excreted dailyrine excreted daily in adults: in adults: ccacca 1.5L 1.5L The renal bThe renal blood flowlood flow== 20% of 20% of cardiac outputcardiac output Plasma renal flow= PRF ca 600 mL/Plasma renal flow= PRF ca 600 mL/MMin./1.73 Min./1.73 M2 2
Reflects two processes Reflects two processes UltrafiltrationUltrafiltration (GFR) (GFR): 180: 180 L/dayL/day Reabsorption: >99%Reabsorption: >99% of the amount filtered of the amount filtered
How do you know it’s broken?How do you know it’s broken?
Decreased urine Decreased urine productionproduction
Clinical Clinical symptomssymptoms
TestsTests
Filter
Processor
InputArterial
OutputVenous
OutputUrine
Causes of kidney functional disordersCauses of kidney functional disorders
Pre-renal Pre-renal e.g. e.g. decreased decreased intravascular intravascular volumvolume e
Renal Renal e.g. e.g. acute acute tubular necrosistubular necrosis
Postrenal Postrenal e.g.e.g. ureteral ureteral obstructionobstruction
Renal Function Tests- Urine volumes
Renal Function Tests- Urine volumes
AAddults: ults: 1.5 L/24 h1.5 L/24 h
typical in healthtypical in health, , oliguria < 400 mLoliguria < 400 mL, , anuria < 100 mLanuria < 100 mL, , polyuria > 3000 mLpolyuria > 3000 mL Children: ca 1.5 ml/Kg Children: ca 1.5 ml/Kg
Principle of ClearancePrinciple of Clearance
Some substances when filtered enter the tubules Some substances when filtered enter the tubules are are not reabsorbed and so not reabsorbed and so 100% excreted and 100% excreted and so they will be equal to so they will be equal to GFRGFR
An example is creatinine which is an An example is creatinine which is an endogenous substances formed constantly in the endogenous substances formed constantly in the bodybody
Clearance= Clearance= GFRGFR = U/P * V = U/P * V
(V=volum(V=volumee of urine of urine, U= Concentration of substance in , U= Concentration of substance in urine, P= concentration of substance in plasma)urine, P= concentration of substance in plasma)
Plasma urea (BUN)Plasma urea (BUN)
= BUN (= BUN (bblood lood uurea rea nnitrogen)itrogen)Urea: product of protein catabolismUrea: product of protein catabolismSynthesized by liver,Synthesized by liver, m majority ajority
excreted by kidneyexcreted by kidney, partially , partially reabsorbed in tubulireabsorbed in tubuli
Plasma concentration increases with Plasma concentration increases with decreased GFRdecreased GFR
Enzymatic conductivity rate method for measuring ureaEnzymatic conductivity rate method for measuring urea
UreaseUreasesolutionsolution
Urea + 3H2OUrea + 3H2O
HCO3¯ + 2NH4 + OH¯HCO3¯ + 2NH4 + OH¯
ureaseurease
Urea in patients with kidney diseases
Urea in patients with kidney diseases
Useful test but must be interpreted with Useful test but must be interpreted with great caregreat care, urea plasma level is more than , urea plasma level is more than creatinine dependent on protein intake creatinine dependent on protein intake Most useful when considered along with Most useful when considered along with creatininecreatinine
High in high protein intake, low in severe High in high protein intake, low in severe liver dysfunction liver dysfunction
Plasma creatinine and renal functionsPlasma creatinine and renal functions
CreatineCreatine: main storage compound of hi: main storage compound of high gh energy phosphate needed for muscle metabolism energy phosphate needed for muscle metabolism..
Creatinine: anhydride of creatine!Creatinine: anhydride of creatine!
CreatineCreatine CreatinineCreatinine
((Waste product)Waste product)H2OH2O
Jaffe´ reaction for measuring creatinine, simple, but better is enzymatic method
Jaffe´ reaction for measuring creatinine, simple, but better is enzymatic method
Creatinine + alkaline picrate solutionCreatinine + alkaline picrate solution
Bright orange/red colored complexBright orange/red colored complexabsorbs light at 485nmabsorbs light at 485nm
Analytical methods (Cr) Analytical methods (Cr)
Normal rNormal rangeange P Pcrcr
Male 0.6-1Male 0.6-1..2 mg/dL2 mg/dL,,
Female 0.5-1.0 mg/dLFemale 0.5-1.0 mg/dL
Osmolality of urineOsmolality of urine
Measures urine concentrating abilityMeasures urine concentrating ability Depends on # of particles, not size or chargeDepends on # of particles, not size or charge Largely due to ADH (Largely due to ADH (aanti-nti-ddiuretic iuretic hhormone)ormone) Can reach maximum of 1200 mOsm/LCan reach maximum of 1200 mOsm/L Normal range:Normal range: 300-900mOsm/L300-900mOsm/L, plasma , plasma
285285++1010 prior to collection, fluid intake restricted, first prior to collection, fluid intake restricted, first
void submitted for evaluationvoid submitted for evaluation