This document discusses renal function tests and their use in evaluating kidney function. It describes the key functions of the kidney including fluid balance, waste excretion, blood pressure regulation, vitamin D and erythropoietin production. Tests are classified as evaluating glomerular function like glomerular filtration rate (GFR) tests or tubular function. GFR is best measured by creatinine clearance or equations using creatinine, age, and other factors. Urine and blood tests can indicate glomerular or tubular dysfunction. Clearance tests measure the removal of substances from blood by the kidneys. Renal biopsy may be used to diagnose kidney disease when function tests are unclear.

1. RENAL FUNCTION TESTS
By-
Dr. Amita Yadav
MBBS, MD (Pathology)

2. Functions of kidney---
• Maintenance of extracellular fluid volume
• and composition.
• Excretion of metabolic waste products.
• Regulation of blood pressure.
• Synthesis of erythropoietin.
• Production of vitamin D3

3. Factors affecting renal function---
•Pre renal conditions- decrease in renal blood flow as in
dehydration,congestive cardiac failure and shock.
•Diffuse renal disease.
•Post renal conditions- obstruction to urinary outflow.

4. Indications for renal function tests---
 Early identification of impairment of renal function in
patients with 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 drug doses according to renal function.

5. Conditions with increased risk of chronic
renal disease---
Diabetes Mellitus
Hypertension
Autoimmune diseases like SLE
Older age
Family history of renal disease
Systemic infection
Urinary tract infection
Lower urinary tract obstruction

6. Classification of renal function tests---
Routine urine analysis- 1. Physical examination
2.Chemical examination
3. Microscopic examination
Tests to evaluate glomerular function
Tests to evaluate tubular function

7. Tests to evaluate glomerular function---
 Clearance tests to measure GFR-
Inuline clearance
I125-iothalamate clearance
Cr51 EDTA clearance
Cystatin C Clearance
Creatinine clearance
Urea clearance

8. Glomerular Filtration Rate (GFR )-
 Best test for assessment of excretory renal function.
 Rate in ml/min at which a substance is cleared from
circulation by glomeruli.
 Normal GFR in young adults is 120-130 ml/min/1.73m2
 Creatine claerance is most commonly used as a
measure of GFR.
 GFR varies according to age,sex and body weight of
an individual,it also depends upon renal blood flow and
pressure.

9. Significance of GFR---

10. Blood Biochemistry---
 Serum creatinine
 Blood urea nitrogen (BUN)
 BUN/Serum creatinine ratio

11. Tests to evaluate tubular function---
 Tests to assess proximal tubular function-
Glycosuria,phosphaturia,uricosuria
Aminoaciduria
Tubular proteinuria
Fractional sodium excretion

12. Tests to assess distal tubular function—
 Specific gravity and osmolality of urine
 Water deprivation test and water loading test
 Ammonium chloride loading test

13. Clearance tests-
Clearance of a substance refers to the volume of
plasma,which is completely cleared of that
substance per minute.
 CLEARANCE = U V / P
U- concentration of a substance in urine in mg/dl
V- Volume of urine excreted in ml/ min
P- concentration of a substance in plasma in mg/dl

14. Properties of agents used for measurement
of GFR-
 Physiologically inert
 Preferably endogenous
 Freely filtered by glomeruli
 Neither reabsorbed nor secreted by renal tubules
 Should not bind to plasma
 Should not be metabolised by kidneys
 Should be excreted only by kidneys

15. Agents used for measurement of GFR-
 Exogenous- Inulin,
Cr51- EDTA ,
I125-iothalamate
 Endogenous- Creatinine,
Urea,
Cystatin C

16. Inulin clearance---
 Inert fructose polymer
 Ideal agent for measuring GFR-Freely filtered by
glomeruli,neither reabsorbed nor secreted by
tubules.
 Bolus dose- 25 ml of 10% solution iv
 Constant iv infusion 500 ml of 1.5% solution at the
rate of 4 ml/min
 Gold standard but rarely used because it is time
consuming,expensive,constant iv infusion
needed,difficulty in laboratory analysis.

17.  Inulin clearance in a healthy young adult has mean
value of
127 ml/min/1.73 m2 – Men
118 ml/min/1.73 m2 - Women

18. Clearance of radiolabelled agents---
( I125-iothalamate,Cr51-EDTA, Tc99-DTPA)
 Expensive
 Risk of exposure to radioactive substances.

19. Clearance of Cystatin C---
 Cysteine protease inhibitor
 Completely reabsorbed by proximal tubule, so its
appearance signifies proximal tubular damage.
 Measured by immunoassay
 More sensitive and specific marker than creatinine
because its level is not affected by sex,diet or
muscle mass.

20. Creatinine Clearance---
 Most commonly used test for measuring GFR.
 Produced constantly by creatine in muscles.
 Completely filtered by glomeruli , is not reabsorbed
by tubules. However a small amount is secreted by
tubules.
 A 24 hour urine sample is preferred to overcome
problem of diurnal variation of creatinine excretion.
 A blood sample for estimation of plasma creatinine
is obtained at midpoint of urine collection.

21. Creatinine clearance= U V / P
• Formula overestimates GFR by 10% because of
secretion of creatinine by renal tubules.
• Level of creatinine is affected by-
Secretion of small amount in renal tubules.
Collection urine is incomplete.
Intake of meat.
Muscle mass.
Certain drugs- Cimetidine,probenecid, trimethoprim

22. Creatinine clearance-
 Men- 110-150 ml/min/1.73 m2
 Women – 105-132 ml/min/1.73 m2

23. Prediction Equations---
( Estimation of creatinine clearance from
serum creatinine )
Cockcroft and Gault Formula-
Creatinine clearance in ml/min =
(140-age in years) x (Body weight in kg )
( 72 x Serum creatinine in mg / dl )
In females value obtained is multiplied by 0.85.

24. SCHWARTZ FORMULA-
CrCl(ml/min/1.73m2) = k x ht in cm/S.Cr(mg/dl)
k = 0.45 ,infants < 1 year of age
k = 0.55 ,children and adolescent
females.
k = 0.7, adolescent males.

25. MDRD formula-
GFR=170 x S.Creat.-0.999 x age-0.176 x BUN-0.170 x
Albumin0.318
(multiplied by 0.742 if female)
( Includes age,race,sex,serum urea nitrogen,serum
creatinine and serum albumin )

26. Simplified MDRD formula-
GFR =186.3 x S.Creat.-1.154 x age-0.203 x 1.212
(multiplied by 0.742 if female)
( Includes age, race, sex, serum creatinine )

27. Urea clearance---
 Urea is filtered by glomeruli but about 40% is
reabsorbed by the tubules.
 Underestimates GFR.

28. Blood biochemistry---
 Blood Urea Nitrogen (BUN)
 Serum Creatinine
 BUN / Serum creatinine ratio

29. Blood Urea Nitrogen---
 Proteins Amino acids
Synthesis of tissue Ammonia
Proteins and Energy Urea Cycle
Other Urea
Compounds
Excretion in urine
Concentration of blood urea is usually expressed as
BUN.

30. Real concentration of urea is BUN x 60/28
Azotemia- Increase in blood level of urea.
Uremia- Clinical syndrome resulting from increase in
blood level of urea.

31. Causes of increase in BUN-
 Pre renal azotemia- shock,congestive heart
failure,salt and water depletion.
 Renal azotemia- impairment of renal function.
 Post renal azotemia- obstruction of urinary tract.
 Increase in rate of production-
High protein diet,
Increase in protein catabolism(trauma,burn,fever)
Gastrointestinal haemorrhage or tissue hematoma.

32. Methods for estimation of BUN-
 Diacetyl monoxime urea method- Direct method.
Urea + Diacetyl monoxime Yellow diazine
derivative
• Urease-Berthelot reaction- Indirect method
Urea
Ammonia+CO2
Hydrolysis in presence of urease
Ammonia + Alkaline hypochlorite + Phenol
Indophenol

33.  Reference range of BUN in adults is 7-18 mg/dl.
 In adults > 60 years ,level is 8-21 mg/dl.

34. Serum creatinine-
 More sensitive and specific marker of renal
function as compared to BUN because-
Level is not affected by diet,protein catabolism or
other exogenous factors.
 Not a sensitive marker for early renal impairment
because significant increase in serum creatinine
does not occur until about 50% of kidney function is
lost.

35. Reference range of serum creatinine-
 Adult males- 0.7 – 1.3 mg/dl
 Adult females - 0.6-1.1 mg/dl
 Causes of increase in serum creatinine-
Pre renal,renal and post renal azotemia
Large amount of dietary meat
Active acromegaly and gigantism

36. Causes of decreased serum creatinine-
 Pregnancy
 Increasing age
 Methods of estimation of Serum creatinine-
Jaffe’s reaction
Enzymatic methods

37. Jaffe’s reaction ( Alkaline picrate
reaction )-
 Creatinine reacts with picrate in alkaline solution to
produce a yellow red colour.
 Non creatinine chromogens-
o Glucose,
o Fructose,
o Protein,
o Ascorbic acid,
o Acetoacetate,
o Acetone,
o Cephalosporin
Cause false elevation of serum creatinine level.

38. BUN/Serum Creatinine ratio-
 Normal ratio is 12:1 to 20:1
 Used to discriminate pre renal and post renal
azotemia from renal azotemia.

39. Microalbuminuria -
 Albuminuria in the range of 30-300 mg/ 24 hours.
 Earliest evidence of glomerular damage.
Macroalbuminuria –
• Albuminuria >300 mg/24 hours.
• Indicates significant glomerular damage.

40. Tests to evaluate proximal tubular
function-
 Glycosuria
 Generalized aminoaciduria
 Tubular proteinuria( normally low molecular weight
proteins are completely reabsorbed by proximal
renal tubule ).
 Urinary concentration of sodium ( Increases in acute
tubular necrosis).
 Fractional excretion of sodium ( FENa)

41. FENa =
Urine sodium x Plasma creatinine x 100
Plasma sodium x Urine creatinine
Values above 3% are strongly suggestive of acute
tubular necrosis.
(Refers to percentage of filtered sodium that has been
absorbed and percentage that has been excreted.)

42. Tests to assess distal tubular function-
 Urine specific gravity
 Urine osmolality
 Water deprivation test
 Water loading antidiuretic hormone suppression test
 Ammonium chloride loading test

43. Urine specific gravity --
 Normal specific gravity is 1.003 to 1.030
- It depends on amount of solutes in solution.
- It reflects the relative degree of concentration
or dilution of a urine specimen.
- It helps in evaluating the concentrating and
diluting abilities of the kidneys
- Urea( 20 %) ,Na Cl (25%), Sulphate ,
Phosphate – major contributors

44.  Increase in specific gravity-
Diabetes mellitus
Nephrotic syndrome
Fever
Congestive heart failure
 Decrease in specific gravity-
Diabetes insipidus
Compulsive water drinking
• Isosthenuria -Specific gravity is fixed (1.010 )

45. Measurement of specific gravity-
1. Urinometer method-
Based on principle of buoyancy
2. Refractometer method-
Measures refractive index of dissolved
solids
3. Reagent strip method-
indirect method .
3 main ingredients : polyelectrolyte ,
indicator and a buffer.

46. Urinometer-

47.  Urinometer is a hydrometer that is calibrated to
measure the specific gravity of urine at a specific
temperature, usually at 200C.
 Based on principle of buoyancy so the urinometer
will float higher in urine than in water, because urine
is denser.
 Thus higher the specific gravity of a specimen, the
higher the urinometer will float.

48.  Specific gravity is affected by presence of dense
molecules, protein and glucose.
Temperature correction-
 For every 30C below 200C, subtract 0.001 from the
reading and for every 30C above 200C, add 0.001.
 Subtract 0.003 from specific gravity after
temperature correction for each 1 g/dl of protein and
0.004 for each 1g/dl of glucose.

49. Urine Osmolality---
 Most sensitive method for determination of ability of
concentration by renal tubule.
 Measures number of dissolved particles in a
solution.
 Expressed as milliosmol/kg of water.
 Measured by osmometer.
 Urine/Plasma osmolality ratio is helpful in
distinguishing pre renal azotemia from acute tubular
nacrosis. ( Higher in pre renal azotemia ).

50. Water Deprivation Test-
 Water intake is restricted for specified period of time
followed by measurement of specific gravity or
osmolality.
 Normally urine osmolality should rise.
 If it fails to rise ,then desmopressin is administered
to differentiate between central diabetes insipidus
and nephrogenic diabetes insipidus.

51.  If urine osmolality is >800 mOsm/kg of water or
specific gravity is more than or equal to 1.025
following dehydration,concentrating ability of renal
tubules is normal.

52. Water loading Antidiuretic Hormone
suppression test--
 This test assesses capacity of kidney to make urine
dilute after water loading.
 After overnight fast ,patient empties the bladder and
drinks 20ml/kg of water in 15-30 minutes.
 Urine is collected at hourly intervals for next 4 hours
for measurement of urine volume,specific gravity
and osmolality.
 Plasma level of ADH and serum osmolality should
be measured at hourly intervals.

53.  Normally >90% of water should be excreted in 4
hours.
 Specific gravity should fall to 1.003 and osmolality
should fall to <100 mOsm/kg.
 In renal function impairment urine volume is
reduced(<80% of fluid intake is excreted ).
 Specific gravity and osmolality fail to decrease.

54. Ammonium Chloride Loading Test—
(Acid Load Test)
 Gold standard for the diagnosis of distal or type 1
Renal tubular acidosis.
 Urine pH and plasma bicarbonate are measured
after overnight fasting.
 If pH is < 5.4 ,acidifying ability of renal tubules is
normal.
 If pH is > 5.4 and plasma bicarbonate is low
Diagnosis of RTA is confirmed.

55.  If neither of above results is obtained patient is
given ammonium chloride orally ( 0.1 gm/kg )over
one hour after overnight fast and urine samples are
collected for next 6-8 hours
 Ammonium chloride makes blood acidic.
 If pH is <5.4 in any one of the samples,acidifying
ability of renal tubules is normal.

56. Renal Biopsy--
 Refers to obtaining a small piece of kidney tissue for
microscopic examination.
 Helpful for-
Establishing the diagnosis.
Assess severity and activity of disease.
Assess prognosis.
To plan treatment and monitor response to therapy.

57. Indications for Renal Biopsy --
 Nephrotic syndrome in adults
 Nephrotic syndrome not responding to corticosteroids in
children.
 Acute nephritic syndrome.
 Unexplained renal insufficiency
 Asymptomatic hematuria
 Isolated non nephrotic range proteinuria with renal
impairment.
 Impaired function of renal graft
 Involvement of kidney in systemic diseases like SLE
and amyloidosis.

58. Contraindications--
 Uncontrolled severe hypertension
 Haemorrhagic diathesis
 Solitary kidney
 Renal neoplasm
 Large and multiple renal cysts
 Small shrunken kidney
 Acute urinary tract infection like pyelonephritis.
 Urinary tract obstruction.

59. Complications--
 Haemorrhage
 Arteriovenous fistula
 Infection
 Perforation of viscus
 Death (rare )

60. After taking biopsy sections are stained
by-
 Hematoxyline and eosine – For general architecture
of kidney and cellularity.
 Periodic acid Schiff – To highlight basement
membrane and connective tissue matrix.
 Congo red – For amyloid.