CLEARANCE TESTS AND SIGNIFICANCE

M.PRASAD NAIDUMsc Medical Biochemistry,Ph.D Research scholar.

FUNCTIONS OF KIDNEY

REMOVES WASTE PRODUCTS

REMOVES FOREIGN AND NON ENDOGENOUS

SUBSTANCES

MAINTAINS ELECTROLYTES AND WATER

MAINTAINS ACIDBASE BALANCE

HORMONAL FUNCTIONS

FORMATION OF URINE

• NEPHRON----FUNCTIONAL UNIT OF KIDNEY• NEPHRON CONTAINS a)GLOMERULUS b)TUBULES

• 1000 to 2000 ml of urine is excreted/day

1)STEPS IN URINE FORMATION Glomerular filtration

tubular reabsorption tubular secretion

GLOMERULAR FILTRATION

700ml of plasma passes through kidneys per minute.

From this 120 to125 ml is filtered per/minute by kidneys.

THIS IS GFR.

GFR DECREASES

GFR DECREASES IN 1. OCCLUSION OF AFFERENT

ARTERIOLES

2. DECREASED PERMEABILITY OF THE MEMBRANE.

3. INCREASED INTRA CAPSULAR PRESSURE

GFR INCREASES IN

1. INCRESED BP2. DECREASED BLOOD PROTEIN

OSMATIC PRESSURE3. INCRESED GLOMERULAR

PERMEABILITY

Effective filtration pressure

• Is the result of A)The glomerular pressure in

glomerular capillaries B)The opposing osmotic pressure of

plasma proteins&Hydrostatic pressure of Bowmens capsule fluid

• Capillary pressure=75 mmHg• Osmatic pressure of plasmproteins=30mmHg

Net effective filtration pressure

• Pef=Pg-(Ppp+Pbc) = 75-(30+20) • Pef=25mmHg• Pg=hydrostatic pressure in the glomerular

capillaries• Ppp=osmotic pressure of plasma proteins• Pbc=hydrostatic pressure of the bowmans

capsule fluid

RATE OF FILTRATION IS INFLUENCED BY

• Variation in BP in glomerular cappilary• Concentration of plasma proteins• Factors altering intratubular pressure viz. a) rise with ureteral obstruction b) during osmotic diuresis c) state of blood vessels

THE VOLUME OF GLOMERULAR FILTRATE FORMED DEPENDS ON:

• The number of glomeruli functioning at a time,• The volume of blood passing through the glomeruli

per minute and• The effective glomerular filtration pressure• In normal circumastances 700ml of plasma flow

through the kidneys per minute& 120 to125ml of fluid is filtered in to bowmans capsule

Volume of filtrate reduced in extra renal conditions

• 1.Dehydartion• 2.Oligemic shock• 3.Cardiac failure• 4.lower the glomerular filtration pressure

• TUBULAR REABSORPTION Formation of primary urine is 120 to 125 ml/mt.

• Only 1 to 2ml/mt reaches the bldder,• 170 litres of water filtered through the glomeruli

&only 1.5 litre is excreted in the urine. So,99% glomerular filtrate is reabsorbed in the tubules

• TUBULAR SECRETION• Examples of substances secreted by the tubular

epithelium are creatinine&potassium

RENAL FUNCTION TESTS

1.TEST BASED ON GLOMERULAR FILTRATION:• Urea clearance test • Endogenous creatinine clearance test • Inulin clearance test • Cr51-EDTA clearance test

2.TESTS TO MEASURE RENAL PLASM FLOW

• Para-amino hippurate test(PAH)• Filtration fraction3.TESTS BASED ON TUBULAR FUNCTION: --Concentration and Dilution tests --15 minute-PSP excretion test --Measurement of tubular secretory massMISCELANEOUS TESTS; Can determine size, shape, anyTumour, obstuction, Infarct etc.

CLEARANCE TESTS

• CLEARANCE;DEFINED AS A VOLUME OF BLOOD OR PLASMA WHICH CONTAINS THEAMOUNT OF THE SUBSTANCE WHICH IS EXCRETED IN THE URINE OR

• THE CLEARANCE OF SUBSTANCE MAY BE DEFINED AS THE VOLUME OF BLOOD OR PLASMA CLEARED OF THE SUBSTANCE FOUND IN ONE MINUTE EXCRETION OF URINE

SALIENT FEATURES OF SUBSTANCE USED FOR CLEARANCE TESTS

a) It must be non toxicb) It should be small enough to pass through

the glomerular membranec) It should neither be secreted nor be

absorbed by renal tubulesd) It should not be metabolised in the body

CREATININE CLEARANCE• CREATININE CLEARANCE: Useful in the diagnosis and

prognosis of the kidney disease.• CREATININE CLEARANCE=

Urine creatinine in mg/dl x Total volume of urine___________________________________

Serum creatinine in mg/dl x 1440REF.RANGE: Male:125ml/mtFemale:115ml/mtA decresed creatinine clearance is very sensitive indicator of a

reduced glomerular filtration rate, due to acute or chronic damage.

CREATININE

• The kidney reserve is such that only when about 50% kidney function must be lost before creatinine level in blood is raised.

• But serum creatinine minor change in concentration may be of significance, and the serum level usually parallel to the severity of the disease.

CREATININE • CREATININE:REF.RANGE:800---2000mg/day.• Creatinine is a waste product formed from Creatinine phosphate which is stored form of the energy in

muscle. this conversion is spontaneous, non enzymatic process and is dependant on total muscle mass and this mass is not affected by diet,age,sex or exercise.

• Since the production is continuous and it is not affected by other factors that’s why Creatinine is an ideal substance for clearance test. This test is mainly to assess the glomerular filtration. GFR provides the most useful index for the assessment of the severity of renal disease.

24 hour urine collection

A 24 hour urine collection is a simple diagnostic procedure that measures the components of urine. The test is cheap, sensitive and is used to assess kidney function, hormones other substances can also be estimated

RISKS OF THE PROCEDURE• 24 hour urine collection is a safe, noninvasive procedure that

is usually done without direct assistance.• Certain factors or conditions may interfere with the accuracy

of a 24 hour urine collection, include the following• Forgetting to collect some of urine• Going beyond 24 hour collection period and collecting excess

urine• Losing urine from specimen container through spilling• Not keeping urine cold during collection period• Acute stress• Vigorous exercise

PATIENT EDUCATION:

• The accuracy of the test results depends on the accuracy of the specimen collection

• Collect in a clean environment• It is important that dust from clothing not contribute

to the specimen content• Do not collect urine in metal glass containers• Females: Do not collect urine while menstruating

PATIENT INSTRUCTIONS• CAUTION: The collection bottle may contain a

preservative in the form of tablets or strong acid solution which may burn your skin.

• Do not remove preservative from the bottle• Keep the bottle upright so it does not spill• Do not urinate directly in to the bottle• Keep out of reach of children• If liquid in the bottle is spilled or splashed, wash

immediately.

PATIENT INSTRUCTIONS

• Record the time and date on the collection container label as the START TIME AND DATE. Also record the time and date in the FINISH TIME/DATE--------space provided on the laboratory requisition

• Deliver the container and lab requisition to the laboratory immediately the collection is finished.

PRESERVATIVES

• Preservatives to be added to 24 hour urine collection for various biochemical estimation

• Amylase, sodium, potassium and chloride-------------- no preservative

• C peptide, cortisol, lead and zinc------------------------- no preservative

• Protein and citrate------- no preservative• Uric acid--------- no preservative

PRESERVATIVES

• Calcium,phosphorous---10ml 6N HCL• VMA,OXALATE-----------10ml 6N HCL• CREATININE,UREA------10ml 6N HCL • PROTEIEN AND CREATININE--------------10ml 6N HCL

CREATININE CLEARANCE

• This is covenient method &sensitive indicator for GFR• ADVANTAGE OF CREATININE CLEARANCE;

– A)It is a normal metabolite of the body– B)It does not require I.V. administration– C)Estimation of creatinine is simple– D)In early stages it has got advantage over S.Creatinine

• CR.CLEARANCE=UV/P• In the calculation surface area is important• Body surface area is calculated from• LogA=0.425 LogW+0.725 LogH -2.144

CREATININE CLEARANCE

• This is covenient method &sensitive indicator for GFR• ADVANTAGE OF CREATININE CLEARANCE;

– A)It is a normal metabolite of the body– B)It does not require I.V. administration– C)Estimation of creatinine is simple– D)In early stages it has got advantage over S.Creatinine

• CR.CLEARANCE=UV/P• In the calculation surface area is important• Body surface area is calculated from

LogA=0.425 Log SW+0.725 log H-2.144

A=Body surface area in meter squareW=Weight in Kg H=Height in cm

• Standard body surface area is 1.73 m²• Creatinine clearance corrected for body

surface area Calculated asUxV x 1.73/PxAMale normal value=125 ml/mtFemale normal value=115 ml/mt

A rough estimate of Creatinine clearancein Males=(140-Age) x Wt in Kg/72 xPcr

• C cr in Females=0.85 xCcr• CREATININE COEFFICIENT=URINARY CREATININE EXPRESSED IN mg/kg body weightNormal range in Males 20 to 28mg/kg Females 15 to 21mg/kgFactor for converting mg/kg/ to nmol/kg/=0.00884Value increses in Muscular Dystrophy

P/C RATIO

• Creatinine estimation is also useful in the muscular dystrophy and in Nephrotic syndrome.

• P/C RATIO=protein concentration in mg/dl___________________________________ creatinine concentration in mg/dlp/c ratio ref.range=< 1P/C ratio increases in NEPHROTIC SYNDROME

M/C RATIO

• MC RATIO=mg of micro albumin/gms of creatinine

• AS PER AMERICAN DIABETIC ASSOCIATION• NORMAL VALUE IS LESS THAN 30 mg of

uma/gm creatinine• Abnormal 30 to 299 Microalbuminemia• More than 300 Maacroalbuminemia

INULIN CLEARANCE

• 10 gm of Inulin is dissolved in 100ml of saline is injected I.V at a rate of 1 ml/mt over 2 hours I.C=UV/P ml/mt

• U=concentration of inulin in urine in mg/dl• V=volume(ml) of urine passed /mt• P=concentration of inulin in plasma in mg/dl• I.C=125ml i.e GFR=125ml• Similar clearance value is seen with

MANNITOL,SORBITOL&DULCITOL

INULIN CLEARENCE DECRESES IN

• Decrease in renal flow• Obliteration or decrese in number of functioning glomeruli• Defect in the effective glomerular filtration pressure• Used to know the substance reabsorbed• Urea reabsorbed in tubules=I.C-UREA CLEARANCE • -----------------------------• I.C 125-75• -------=0.4 SO,40% OF UREA REABSORBED 125

UREA CLEARANCE

• Maximum clearance; If the urine volume exceeds 2 ml/mt.

• Volume of blood cleared of urea/mt=UV/P =1000 X 2.1/28=75

• Standered clearance;when the urinary volume is less than 2ml/mt

• Cs=Ux square root of √V/P=54 ml• Only 60% of glomelular filtrate urea excreted• Urea clearance is 60% of Inulin clearance =UC/0.6=I.C

Determination of CR₅₁ EDTA CLEARANCE

• SINGLE INJECTION IS USED FOR GFR ESTIMATION

• USED FOR CHILDREN &ADULTS• CONVENIENT FOR CHILDREN WHERE IT IS NOT

EASY TO COLLECT 24 HOUR URINE.

THANK YOU