Renal function Renal function

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

Urea cycleUrea cycle

CO2CO2NH3NH3

aspartateaspartate

UreaUrea

3 ATP3 ATP

UreaUreaCycleCycle

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