Laboratory tests of renal function Junfu Huang Southwestern Hospital TMMU

Anatomy of Kidney

Functions of the kidney ä Excretion of Metabolite Waste: urea, uric acid,cretinine ä Urine Production,regulation of homeostasis, water, acid base balance ä Endocrine Function: renin, erythropoietin, 1,25 - dihydroxycholecalciferol

Renal function tests ä Detect renal damage ä Monitor functional damage ä Distinguish between impairment and failure

Kidney Function ä A plumbers view

How do you know it’s broken? ä NO Urine! ä Clinical symptoms ä Tests

Where can it break? ä Pre-renal ä Renal ä Post-renal

Laboratory tests of renal function ä Glomerular Function Tests ä Renal Tubular Function Tests

Section 1 Investigation of Glomerular Function ä Renal Blood Flow: ml/min ä Renal Plasma : ml/min ä 20% of plasma: glomerular filtration GFR:Glomerular Filtrtion Rate GFR:Glomerular Filtrtion Rate Concept Concept

Renal Clerance ä Concept Virtual volume of plasma from which the substance in question has been completely removed during a given time interval. Virtual volume of plasma from which the substance in question has been completely removed during a given time interval. C=UV/P C=UV/P U:urine concentrtion P:plasma con. U:urine concentrtion P:plasma con. V:urine flow rate V:urine flow rate

Usefulness of Renal Clerance ä Freely filtrated, neither secrected,nor reabsorbed: Inulin:GFR Determination ä Freely Filtrated, small amounts secreted,whithout reabsoption:Cretinine:GFR ä Free filtrated,completelyeabsorption:Glucose Tubular Maxima Reabsorption Rate Tubular Maxima Reabsorption Rate

Inulin Clerance ä Polymer of fructose ä MW:5500 ä Free filtration,without secretion and reabsorption ä GFR ä Method ä Reference Interval: ml/min

Endogenous Creatinine Clearance ä 100g,98% stored in musle,MW:113 ä Cretine psosphate---cretine—cretinine ä Freely filtration, small mounts:secretion ä Exogenous and Endogenous Creatinine ä Grossly Investigate the GFR

ä Method 24h urine collection method 24h urine collection method modified 4h urine collection method modified 4h urine collection method Clerance Correction ： Clerance Correction ： Ccr x SBSA/IBSA Ccr x SBSA/IBSA

Plasma urea ä Serected and reabsorbed by tubules,freely filrtated ä quick, simple measurement ä wide reference range mmol/L ä sensitive but non-specific index of illness

Urea excretion ä filtered at glomerulus ä about 40% filtered urea is reabsorbed by renal tubules in health ä more urea is reabsorbed if rate of tubular flow is slow ä tubular flow rate is slow when there is renal hypoperfusion

Increased plasma urea ä GI bleed ä trauma ä renal hypoperfusion decreased RBF decreased ECFV ä acute renal impairment ä chronic renal disease ä post-renal obstruction calculus tumour

Urea ä Useful test but must be interpreted with great care ä Always consider input, output and patient’s fluid volume

Plasma creatinine ä umol/L ä increases in concentration as GFR decreases ä analytical interferences ä (acetoacetate - DKA) ä NOT proportional to renal damage

Plasma Creatinine GFR [pCreat] 140 mL/min 0 mL/min Change within an individual patient is usually more important than the absolute value

Plasma creatinine in chronic renal disease ä May increase to 1000 umol/L ä Plot of recipricol of plasma creatinine concentration predicts when intervention is required in end stage renal failure Time 1/ [pCreat]

Plasma Uric Acid ä 20%:foods;80%:purine metabolism ä Small amounts: conjugated with albumin ä Free Filtrated,98%-100%:reabsorbed ä Plasma UA concentration: depend on glomerular filtration and tubular reabsorption

Progression of chronic renal disease

Plasma Cystatin C ä Cysteine proteinase inhibitor ä Produced by nucleated cells ä MW:13000, free filtration,reabsorbed and metabolized by tubules ä Plasma CysC concentrtion: depend on glomerular filtration

Carbamylated hemoglobin ä Urea—blood—cyanate—Hb carbamylated—CarHb ä ARF ： no changes(1 weeks) ä CRF: increase

Laboratory tests of renal function ä glomerular filtration rate impractical ä creatinine clearance unreliable ä plasma creatinine specific but insensitive ä plasma urea subject to problems ä urine volume often forgotten!

Section 2 Investigation of Tubular Function ä Distal nephron Function tests 1. Mosenthal test 1. Mosenthal test Concentration dilution test Concentration dilution test 8 AM :Voiding and Discarded 8 AM :Voiding and Discarded 10,12,14,16,18,20:00 and 8:00 next day: 10,12,14,16,18,20:00 and 8:00 next day: collecting urine samples collecting urine samples Determing the urine volume and gravity Determing the urine volume and gravity

ä 2.Urine Osmolarity ä 3.Acute Oliguria Prenal? Prenal? Renal? Renal?

ä Proximal tubular Function tests 1.Low MW proteins in urine 1.Low MW proteins in urine 2.Tubular maximal glucose reabsorption 2.Tubular maximal glucose reabsorption 3.Tubular maximal PAH secretion 3.Tubular maximal PAH secretion 4.Amino acide in urine 4.Amino acide in urine Fanconi Syndrome Fanconi Syndrome

Section 3 Effective Renal Blood Flow ä Isotope Method: 131 I-OIH ä PAH Clearance: 20%:filtrated,80%:secreted by tubules 20%:filtrated,80%:secreted by tubules

Section 4 Investigation of renal tubular acidosis ä Tubular Acidosis:I,II,III.IV ä I:distal form ä II:proximal form

NH4Cl Loading Test ä Oral administration of NH4Cl ä Artificial Metabolic Acidosis ä Urine Sample Collection ä pH determination

Fraction of HCO 3 - excretion ä HCO 3 - :85-90%: reabsorbed by proximal tubules; 10-15%: reabsorbed by distal tubules ä Oral Administration of NaHCO 3 ä Urine Collection ä Determination of P Cr,U Cr,P HCO3,U HCO3 ä Caculation: FE HCO3 =U HCO3.P Cr /U Cr.P HCO3 FE HCO3 =U HCO3.P Cr /U Cr.P HCO3