Reading of renal function

YY Chiou

Glomerular filtration rate

Clearance of inulinClearance of creatinine:normal range

Male:120±25 mL/minFemale:95±20mL/minInfant:17 mL/min/1.73M2

P[Inulin] × GFR = U[Inulin] × urine volume

Difference between inulin and creatinineAge effect: age >40y/o -> Ccr decrease 1mL/min/yrUrine Cr collection:

Age≦60y/o:male: 20-25mg/kg; female:15-20mg/kgAge>60y/o:10mg/kg

Plasma Cr

Condition associated with PCr increased and not changed GFR

Increased Cr productionRhabdomyolysisMeat

Decreased Cr excretionCimetidine, triamterene, probenecid, amiloride, trimethoprim, spironolactone

Measured biasEndogeneous: ketone, ketoacids, glucose, bilirubin, urate, urea, fatty acidExogeneous: cephalosporines, 5-FU, phenylacetyl urea, acetoheximide

Estimate Ccr

Cockcroft and Gault equation: CCr=[(140-age(yr)) ×BW(kg)] ÷[72×Pcr(mg/dl)]Female: above data×0.851/PcrEsGFR(ml/min/1.73M2)=KL(body length, cm) ÷ Pcr

K LBW:0.33NB-1yr:0.452yr-adolescent girls: 0.552yr-adolescent boys:0.77

BUN

Reverse relationship with GFR, but many confounding factorsUrea nitrogen can reabsorb paralleling with Na and H2O resorptionBUN ： Pcr = 15-20:1

Urinalysis

Urine sample: fresh (30-60min)3000rpm, 3-5min -> suspension with pelletColor

Urine protein

Daily urinary protein:150mg/dayMicroalbuminuriaDetection: dipstick

Tetrabromophenol blue dye –albuminSulfosalicylic acid

Protein(mg/dL) dipstick sulfosalicylic acid0 0 no turbid1-10 trace slight turbid15-30 +1 turbid40-100 +2 white without ppt150-350 +3 white with ppt>500 +4 coarse ppt

Urine protein

24 hr daily protein lossSpot UTP/UCr

Urine pH and osmolality

Normal range:4.5-8.0How about alkalization urine?Urine sp. Gr. To estimate urine osmolalityPlasma osmolality & urine osmolality

Urine Na excretion

Urine excretion = intake Na amountUrine [Na]<20meq/LUrine [Na]>40meq/LSignificance of %FENa

ARF with %FENa <1%

Prerenal factorATN

Non-oliguric ATN (10%)Chronic prerenal disease-Contrast mediaSepsisMyoglobulinuria or hemoglobulinuria

AGN or vasculitisObstructive nephropathy

Urinary cast

Hyaline cast conc. Urine or diuretics

Red cell cast GN or vasculitis

WBC cast TIN, APN, GN

Epithelial cast ATN, GN

Fatty cast GN with proteinuria, NS

Granular cast proteinuria, degenerative cells

Waxy cast CRF

Renal acidification evaluation

Urinary pH: Net acid excretion:Urinary anion gap:Acidification loading test:

Urine pH

Fresh urineCollect in the morningMust rule out UTIMany confounding factors- proton pump, electro-gradient of membrane, buffer conc., diet, et. al.

Net acid excretion

Total acid excretion=titratable acid + NH4

+

Net acid excretion=total acid excretion – HCO3

- excretionTitratable acid= buffer solution of H3PO4 with urea nitrogenDef. of titratable acid excretion:the amount of NaOH(meq) to elevate UpH to 7.4

Urinary anion gap

Total conc. Of anions = total conc. Of cationsNa++K++NH4

++Ca+2+Mg+2=Cl-

+H2PO4-+SO4

-+organic anions

Na++K++NH4+=Cl-+80

Urinary anion gap:Na++K+-Cl-

Urinary acid loading tests

Acid loading testSodium sulfate infusion test or furosemide testBuffer loading test

Acid loading test

NH4Cl 0.1g(1.9meq)/kg, po -> collection urine pH and net acid excretion for 2-8hr.(normal: UpH<5.5)CaCl2

Arginine HCLDiamox testNormal urine CO2>80mmHg

U-B[PCO2]>30mmHg

Increase distal tubule Na conc. Test – for proton pump or voltage-dependent defect

Furosemide test: 1mg/kg, collect urine pH, net acid excretion and U[k], po 5hr or iv 3hr

Reading:UpH increase in 1hr and then UpH down to 5.5 in future 2-4hrs; U[k] and acid increase 2 fold

Sodium sulfate

Buffer loading test

IV drip or 2-3ml/min NaHCO3 100-150mEq(total) till plasma NaHCO3 ≧30meq/L

Then check blood and urine pH, [HCO3-], CO2

Calculate %FEHCO3-

3-5%

>15%

U-B[PCO2] >20-30mmHg, when U[HCO3-] >100-150meq/L