This slides explain the test involve to assess the health of kindey. It include all the test involve to determined the health of kidney

1. DR. ANUYA BADWE
KIDNEY FUNCTION TESTS

2. Functions of Kidney
 Maintenance of extracellular fluid volume &
composition
 Excretion of metabolic waste products
 Regulation of blood pressure by renin angiotensin
mechanism.
 Synthesis of erythropoietin
 Production of vit.D3 (active form)

3. Indications
 Early identification of impairment of renal function in
patients with increased risk of chronic renal disease
 Diagnosis of renal disease
 Follow the course of renal disease and assess response to
treatment
 Plan renal replacement therapy (dialysis or renal
transplantation) in advanced renal disease
 Adjust dosage of certain drugs (eg. Chemotherapy)
according to renal function.

4. Classification of Renal Function tests

5. Tests to Evaluate Glomerular Function
 Normal GFR : 120-130ml/min per 1.73 sq.m
 Declines progressively at the rate of 1
ml/minute/year after 40 years of age

6. Clearance Tests to Measure Glomerular Filtration
Rate
 If a substance is not bound to protein in plasma, is
completely filtered by the glomeruli, and is neither
secreted nor reabsorbed by the tubules, then its
clearance rate is equal to glomerular filtration rate.
 Clearance=UV/P
 U=concentration of a substance in urine in mg/dl
 V=volume of urine excreted in ml/min
 P=concentration of the substance in plasma in mg/dl

7.  Inulin clearance
 Clearance of Radiolabeled Agents
 Cystatin C clearance
 Creatinine clearance
 Urea clearance

8. Inulin Clearance
 Inulin is an inert plant polysaccharide, is filtered by
glomeruli & is neither reabsorbed nor secreted by the
tubules.
 A bolus dose (25 ml of 10% IV)is administered followed
by constant IV infusion (500ml of 1.5% soln at the rate of
4ml/min)
 Timed urine samples are collected & blood samples are
obtained at the midpoint of timed urine collection.
 Normal inulin clearance for males:90-139ml/min/1.73sqm
 Normal inulin clearance for females:80-125ml/min/1.73sqm

9.  Clearance of radiolabeled agents: 51Cr-EDTA &
99Tc-DTPA
 Cystatin C clearance:
cystine protease inhibitor is produced by all
nucleated cells at constant rate.
Its level is not affected by sex, diet or muscle
mass.
It is measured by immunoassay.

10.  Creatinine clearance:
completely filtered by glomeruli & not
reabsorbed by tubules.
A 24 hr urine sample is preferred to overcome
problems of diurnal variation.
It is derived from formula C=UV/P
 Men :110-150 ml/min/1.73 sqm
 Women : 105-132 ml/min/1.73 sqm

11.  Urea clearance
 Urea is filtered by the glomeruli, but about 40% of the filtered
amount is reabsorbed by the tubules.
 The reabsorbtion depends on the rate of urine flow.
 Thus, it underestimates GFR, depends on the urine flow rate &
not a sensitive indicator of GFR.

12. Estimation of Creatinine Clearance from Serum
Creatinine by Prediction Equations
 Creatinine clearance in ml/min =
(140-Age in years) x (Body weight in kgs)/
(72 x Serum creatinine in mg/dl)
In females, the value obtained from above equation is multiplied
by 0.85 to get the result.

13. Blood Biochemistry
 Blood Urea Nitrogen :
 Methods
 Diacetyl-monoxime method
 Berthelot reaction
 UV kinetic method
 Adults : 7-18 mg/dl
 >60 yrs : 8-21 mg/dl

14.  Causes of increased BUN:
1) Pre renal azotemia : shock, ccf, water & salt deprivation
2) Renal azotemia: impairment of renal function
3) Post renal azotemia : urinary tract obstruction
4) Increased rate of production of urea:
High protein diet
Increased protein catabolism (trauma, burns, fever)
Absorbtion of amino acids & peptides from large haemorrhage in
GIT

15. Blood Biochemistry
 Serum Creatinine
Methods
 Jaffe’s reaction
 Kinetic method
 Adult males : 0.7-1.3mg/dl
 Adult females : 0.6-1.1mg/dl
 Males <20 yrs : 0.35 + age in years/40
 Females <20 yrs : 0.35 + age in years/55

16.  Causes of increased serum creatinine :
1. Pre renal, renal & post renal azotemia
2.Large amount of dietary meat
3.Active acromegaly & giagantism

17. Blood Biochemistry
 BUN/Serum Creatinine Ratio :
 Normal range : 12:1 to 20:1
 Causes of increased BUN/Creatinine ratio (>20:1)
 Increased BUN with normal serum creatinine
Pre renal azotemia
High protein diet
Increased protein catabolism
 Increase of both BUN & serum creatinine with disproportionately
greater increase of BUN:
Post renal azotemia
Obstruction to the urine outflow causes diffusion of urinary
urea back into the blood from tubules because of back pressure

18. Microalbuminuria and Albuminuria
 Microalbuminuria :30-300mg/24hrs
 Overt albuminuria : >300mg/24hrs
Microalbinuria is the earliest evidence of
glomerular damage in DM

19. Tests to Evaluate Tubular Function
 Tests to Assess Proximal Tubular Function
 Glycosuria
 Generalised aminoaciduria
 Tubular proteinuria
 Urinary concentration of sodium
 Functional excretion of sodium
 [( Urine sodium x plasma creatinine)/(plasma sodium x urine
creatinine)] x 100

20.  Tests to Assess Distal Tubular Function
 Urine specific gravity
 Urine osmolality
 Water deprivation test
 Water loading anti diuretic hormone suppression test
 Ammonium chloride loading test ( Acid load test)

21.  Tests to Assess Distal Tubular Function
 Urine specific gravity- ratio of mass of solution to the mass of
water
 SG is a measure of concentrating ability of kidneys.
 Urinometer method :
Principle of buoyancy i.e. the ability of the fluid to exert
an upward thrust on a body placed in it.
normal value : 1.003-1.030
Increased in DM, Nephrotic syndrome & dehydration
Decreased in diabetes insipidus, CRF & compulsive water
drinking

22.  Tests to Assess Distal Tubular Function
 Urine osmolality –number of dissolved particles in a solution
Urine/plasma osmolality ratio is helpful in
distinguishing pre renal azotemia (in which ratio is
higher) from acute renal failure due to acute tubular
necrosis (ratio is lower)

23.  Tests to Assess Distal Tubular Function
 Water deprivation test
Water intake is restricted for a specified time followed by
measurement of specific gravity or osmolality .
Normally, urine osmolality should rise in response to water
deprivation.
If it fails to rise, then desmopressin is administered.
Urinary concentrating ability is corrected after
administration of desmopressin in central diabetes insipidus, but
not in nephrogenic type.

24.  Tests to Assess Distal Tubular Function
 Water loading anti diuretic hormone suppression test
After overnight fast, patient empties the bladder & drinks 20 ml/kg water
in 15-20 minutes.
Urine is collected at hourly intervals for next 4 hours for measurements of
urine volume, sp. Gravity & osmolality.
Plasma levels of ADH & serum osmolality should be measured at hourly
interval.
Normally >90% water should be excreted in 4hrs.
Specific gravity should fall to 1.003 & osmolality <100 mOsm/kg
If renal function is impaired, urine volume is reduced & sp. gravity &
osmolality fail to decrease.

25.  Tests to Assess Distal Tubular Function
 Ammonium chloride loading test ( Acid load test)
Urine pH & plasma HCO3 levels are measured after overnight fasting.
If pH is < 5.4 , acidifying ability of renal tubules is normal.
If pH is >5.4 & plasma HCO3 is low, diagnosis of renal tubular acidosis
is confirmed.
To confirm further patient is given ammonium chloride (0.1m/kg) over
1 hour after overnight fast & urine samples are collected hourly for next 6-8 hrs.
ammonium ions dissociate into H & NH3 & makes blood acidic.
thus, if pH is <5.4 acidifying ability of the distal tubule is normal.

26. Renal Biopsy
Indications for Renal Biopsy
 Nephrotic syndrome in adults
 Nephrotic syndrome not responding to corticosteroids in children
 Acute nephritic syndrome for differential diagnosis
 Unexplained renal insufficiency with near-normal kidney dimensions on
ultrasonography
 Asymptomatic hematuria, when other diagnostic tests fail to identify the source of
Bleeding
 Isolated non-nephrotic range proteinuria (1-3gm/24hrs) with renal impairment
 Impaired function of renal graft
 Involvement of kidney in systemic lupus erythematous or amyloidosis

27. Contraindications
 Uncontrolled severe hypertension
 Hemorrhagic diathesis
 Solitary kidney
 Renal neoplasm (to avoid spread of malignant cells along the needle track)
 Large and multiple renal cysts
 Small, shrunken kidneys
 Acute urinary tract infection like pyelonephritis
 Urinary tract obstruction

28. Complications
 Hemorrhage
 Arteriovenous fistula
 Infection
 Accidental biopsy of another organ or perforation of
viscus
 Death

29. References
 Henry’s Clinical Diagnosis & Management by
Laboratory Methods, 21st
edition
 Robbins & Cotran Pathologic Basis of Diseases , 8th
edition
 Harrison’s Principles of Internal Medicine , 16th
edition
 Textbook of Medical Laboratory Technology, Praful
B. Godkar, 2nd
edition
 Essentials of Clinical Pathology, Shirish M
Kawthalkar

30. Thank you…!!!