KIDNEY FUNCTION TEST

DR.RITTU CHANDELM.D. BIOCHEMISTRY (2ND YEAR)

GRANT GOVT MEDICAL COLLEGE, MUMBAI21-08-2013

ANATOMY

PHYSIOLOGY

Glomerular filtration

GFR (120 – 130 ml/min/1.73 m2

• Rate of filtration affected by – state of blood vessels concentration of plasma proteinsVolume of glomerular filtrate depends on – number of functioning glomeruli effective glomerular filtration pressureVolume reduced in extra renal conditions

Tubular function• Tubular epithelial cells are highly specialized tissue –

able to reabsorb selectively some substances and secrete others

• 170 l -------filtered• 1.5 l --------excreted• Nearly 99 % reabsorbed• Renal threshold – plasma level above which

compound is excreted in urinesubstance Threshold value

glucose 180 mg/dllactate 60 mg/dlbicarbonate 28 mEq/lcalcium 10 mg/dl

FUNCTIONS

1. Maintenance of homeostasis2. Excretion of metabolic waste products3. Retention of substance vital to body4. Hormonal functiona.Erythropoietinb.Calcitriolc.renin

Preliminary investigation

• History – oliguria, polyuria, nocturia, ratio of frequency of urination in day time and night time, appearance of oedema

• Physical examination• Urine analysis• Biochemical parameters – increase in three

nitrogenous constituents of blood( uric acid, urea, creatinine )others

Renal function tests1. On glomerular filtration• Urea clearance test• Endogenous creatinine clearance test• Inulin clearance test• Cr51 - EDTA clearance test• Tests on glomerular permeability2. Measure renal plasma flow• PAH test• Filtration fraction3. Tubular function• Concentration and dilution tests• 15 min – PSP excretion test4. Miscellaneous test

clearance

• Substance S -----stable concentration in plasma• Physiologically inert, freely filtered at glomerulus,

neither secreted, reabsorbed, non toxic, not affected by dietary intake

• Amount of S entering kidney = amount of S leaving it• Filtered S = excreted S• GFR x Ps = Us x V• GFR = Us x V• Ps

s

Clearance

• Volume of blood or plasma which contains the amount of substance which is excreted in the urine in 1 min

Clearance = U X V PU ---- concentration of substance in urineV----- volume of urine ( ml/minute)P-----concentration of substance in plasma

substance filtered reabsorbed secreted Amount excreted /minute in relation to amount filtered

Glucose

Urea

Creatinine

PAH, phenol red, diodrast

Inulin, mannitol, thiosulphate

Yes

yes

Yes

Yes

yes

Yes, completely( 180 gm/dl)TmG = 350 mg/mt

yes

no

No

No

No

no

no

Yes

no

Not excreted normally

less

Very close

More than that filtered

GFR = clearance

UREA clearance tests

• Maximum clearance( urine volume > or = 2 ml/min)

Standard clearance(urine volume < 2ml /min)

Clearance = U X V P = 1000 x 2.1 28 = 75 ml/ min

Clearance = U X √v P = 54 ml/ min

Expression of result as % = result of clearance is expressed as % of normal maximum or normal standard urea clearance depending on urinary output

Relation with body surface area Cm x 1.73 BS Cs x √1.73

BS

• ProcedureBreak fast lunch

1 hr

1 hr

Empty bladder

Urine and blood collection

Urine collection

Interpretation :Urea clearance ≥ 70% ----------average normal function 40 – 70 % ------mild impairment ≤ 20 % ----------severe impairment

disease Urea clearance

Chronic nephritis Falls progressivelyReaches value half or less of normal before blood urea concentration begins to rise

Terminal uremia About 5 % of normal

Nephrotic syndrome Normal until onset of renal insufficiency

Benign hypertension Normal clearance usually maintained indefinitely

Blood urea• Normal – 20 – 40 mg/dl• Serum concentration increases as age advances

Pre - renal renal Post renal drugs

DehydrationSevere vomitingIntestinal obstructionDiarrheaDiabetic comaSevere burnsFeverSevere infections

Acute glomerulonephritisNephrosisMalignant hypertensionChronic pyelonephritis

Stones in urinary tractEnlarged prostateTumors of bladder

ACEIAcetaminophenAminoglycosidesAmphotericin BDiureticsNSAIDS

Increase in blood urea

Decreased blood urea – late pregnancy, starvation, hepatic failure

Creatinine clearance test

• 113 Da • Produced by muscle from creatine and creatine

phosphate through non enzymatic dehydration process

• 24 hr excretion of endogenous creatinineCcr = U X V PNormal – 95 – 105 ml/min

• procedure

500 ml

water

given

After 30 mins,

bladder emptied and urine

discarded

After 60

mins, urine and

blood sample collect

edadvantages •1.Value close to GFR

•2.Long term monitoring

disadvantages

•1.Mild renal impairment ( creatinine blind area )•2.Moderate impairment (secretion component )•3.Severe impairment (extra renal excretion)

Estimated GFR ( eGFR)• Cockcroft - Gault equationCcr = (140 – age in yrs) x wt(kg) (0.85 in females) x Pcr 72MDRD ( modification of diet in renal disease)eGFR = 186 x {creatinine} - 1.154 ( age ) – 0.203 x 0.742 88.4

Serum creatinine

decrease increase

Low muscle massFemalesMalnutritionThiazidesvancomycin

Old ageMalesGlomerulonephritisPyelonephritisRenal failureUrinary obstructionCCF, dehydration, shockAmphotericin BCaptoprilCephalosporinkanamycin

Normal = 0.7 – 1.5 mg/dl

Inulin clearance test

• Ideal substance• Procedure:Overnight

fast

Light

breakfast at 7:30 am

10 gm inulin in 100

ml saline inj i.v. at 10 ml/min at 8am

Bladder

emptied at 9am, urine discarded

After 30

mins, urine and

blood collec

ted

After 60

mins, urine and

blood collec

tedNormal = 125 ml/min range = 100 – 150 ml/minInulin clearance x 0.6 = maximum urea clearance

Cystatin C

• 122 amino acids, 13000 Da• Inhibitor of cysteine proteinase• Produced by all nucleated cells• Production rate constant• Not affected by muscle mass, sex, race• High isoelectric point, which enable it to be more freely

filtered• Sensitive changes in creatinine blind area• Extremely sensitive to minor changes in GFR • Measurment expensive and difficult

Substances used in clearance testsEndogenous substance – urea, creatinine, cystatin C, β – trace

proteins, β - 2 – microglobulin, tryptophan glycoconjugate

β - 2 – microglobulin

Polypeptide, 11.6 kDa, 99 amino acid

Component of MHC -1

In all nucleated cells

Needed for production of CD-8

tryptophan glycoconjugate

Mannopyranosyl – l – tryptophan (MPT) – produced in body by glycoconjugation of tryptophan

Measured by HPLC

Clearance tests

• Gold standard – inulin ( sinistrin)• Silver standard – Cr51 - EDTA• Tc99 - DTPA • I125 – iothalamate• iohexol• Bronze standard – creatinine• cystatin C• Uncertain clinical use – creatinine clearance• urea• retinol binding protein• α1 - microglobulin

Grading of chronic kidney diseasestate grade GFR ml/min/1.73sq m

Minimal damage 1 >90

Mild damage 2 60 – 89

Moderate damage 3 30 – 59

Severe damage 4 15 – 29

End stage 5 < 15

CKD = GFR < 60 ml/min/1.73 m2 for 3 months or more with or without kidney damage

Test for glomerular permeability

• First sign of glomerular injury (before decrease in GFR)

• Proteinuria• Normal protein excretion = <150 mg/24 hrs

Glomerular damge

•Glomerular proteinuria

Increase in low mol. Wt proteins

•Overflow proteinuria

Decrease in reabsorptive capacity

•Tubular proteinuriaOthers

Nephron loss proteinuriaUrogenic protreinuria

• Glomerular proteinuriaAlbuminuria ( early morning urine sample

prefered)300 mg/day Benign proteinuria300 – 1000 mg/day Pathological proteinuria

>1000 mg/day Glomerular proteinuria

Large quantity of albumin nephrosis

Small quantity of albumin Acute nephritis, pregnancy

Measurment of albuminuria is helpful in monitoring kidney function and response to therapy in many forms of CKD

• Microalbuminuria/ minimal albuminuria/pauci albuminuria30 – 300 mg/day in urineEarliest sign of renal damage – diabetes mellitus, hypertension

Overflow proteinuriaHemoglobinuria (hemolytic anemia)Myoglobinuria ( crush injury)Multiple myeloma

Hematuria –confirms glomerular damage, also earliest sign before decrease in GFR

Tubular proteinuria

Functional nephrons decrease, GFR decreasesRemaining nephrons are overworked

Tubular reabsorption impairedLow molecular wt. protein appear in urine

Hence can be used as markers of tubular damageEg. Β – d –glucosaminidase, lysozyme

Test for renal blood flow

1. Measurment of renal plasma flowPAH - filtered and secreted - removed completely during a single

circulation of blood through the kidneysRPF = 574 ml/min

2. Filtration fraction:Fraction of plasma passing through the kidneyFF = Cin = GFR = 125 = 0.217 ( 21.7%) CPAH RPF 594

Normal range = 0.16 – 0.21disease Filtration fraction

Essential hypertension

Normal in early period, as disease progresses ↓ RPF > ↓ GFR -------FF ↑

Malignant phase of hypertension

↑↑↑↑ FF

glomerulonephritis Greater ↓ in GFR than RPF, ↓FF

Pathophysiology of tubular function

Alteration in Tubular function

Toxic substances

Impairing transfer of substances

across tubular cells

ischemia

Concentration and dilution tests

• Ability to concentrate and dilute urine dependent on:

GFRRPFTubular massHealthy tubular cellsPresence of ADH

Concentration tests/fluid deprivation tests• ability of kidney to concentrate urine• measurement of specific gravity of urine• Simple, bedside procedure• Most sensitive means of detecting early impairment in renal function1. Fishberg concentration test –Procedure:Meal at 7 pm------no fluid from 8 pm to 10 amUrine specimen collected at 8, 9, 10 am Determine specific gravityResult:Specific gravity of any one specimen > 1.025----NORMAL < or = 1.020 ---impaired fixed at 1.010 ----severe

2. Lashmet and newburg concentration testSevere fluid intake restriction over a period of 38

hrs3.With posterior pitutary extracts.c. inj of 10 pressor units of posterior pitutary

extract (0.5 ml of vasopressin inj)Result – specific gravity - > or = 1.020 -----normalFailure to concentrate -----renal damage

Advantages – CCF, DI

Water dilution or elimination test• Ability of kidney to eliminate water is tested

by measuring urinary output after ingesting large volume of water Eve

ning meal at

8 pm

After 12 hrs i.e. 8 am first

urine sampl

e discarded

After 8

am , 1200

ml given

in half hr

Bladder emptied at 9, 10, 11 ,12

Kidney function Urine voided in 4 hrs Specific gravity of at least 1 specimen

normal >1000 ml (80%)Larger part excreted in first 2 hrs)

< or = 1.003

impaired <1000 ml (80%) Doesn’t fall to 1.003Fixed at 1.010 in severe renal damage

Patient in supine position

Test of tubular excretion and reabsorption

• Phenol sulphthalein (PSP) excretion test94%----excreted, 6%----glomerular filtration15 min PSP Test - reliable and sensitiveTest -

1 ml ( 6 mg) inj iv

30 -50 % excreted in 1st 15 mins

<23% excreted in 1st 15 mins

Miscellaneous tests

• Test of renal ability to excrete acidGive

NH4Cl in

gelatin coated capsule (0.1 mg/kg

)

Empty

bladder 1 hr

later, urine discarded

Collect all urine sample

s in next 6

hrs. measur

e pH and NH3

content

Kidney function pH NH3

normal 5.3 30 -90 mEq/min

Renal failure decreases decreases

Renal tubular acidosis

5.7 - 7 decreases

Contraindications : liver disease, acidosis

• IVP• Radioactive scanning• Renal biopsy• Immunological tests1. Anti GBM antibodies2. ANCA3. Pattern of complement in nephritis

GLOMERULAR DYSFUNCTION TUBULAR DYSFUNCTION

Increase in Se urea Urinary concentration decreases

Increase in Se creatinine Dilution tests abnormal

Inulin clearance decreases Uric acid excretion decreases

Creatinine clearance decreases Blood uric acid increases

Urea clearance decreases Acidification of urine decreases

Urine volume decreases Aminoaciduria present

Specific gravity increases Urine volume increases

Se phosphate increases Specific gravity decreases

Poteinuria present Se phosphate decreases

bibliography

• Satyanaryan• Ranna shinde• Vasudevan• Kaplan• Teitz• Varley• Pankaja naik

• THANK YOU