This document discusses renal function tests and their use in assessing kidney function. It covers tests that measure glomerular filtration rate like creatinine clearance and urea clearance. Creatinine clearance is considered the best measure of glomerular filtration as creatinine is filtered at the glomerulus and neither reabsorbed nor secreted. Stages of kidney disease are defined based on glomerular filtration rate. Tubular function tests like urine concentration are also discussed. Biochemical changes in blood that occur with impaired kidney function are outlined.

1. Department of Biochemistry, KMC, Duwakot
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January 20, 2016
Rajesh Chaudhary
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For BDS II

2. Purpose of Renal Function Test
To assess functional capacity of kidneys.
For early detection of possible renal impairment.
To assess severity and progression of renal impairment.
To monitor the response of treatment of renal diseases.
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A stepwise increase in three nitrogenous
components (uric acid, urea, creatinine) of
blood is believed to reflect a deteriorating
kidney function.
-- MN Chatterjea, Textbook of Medical Biochemistry

4. Indications of RFT
 Family history of chronic kidney disease
 Diabetes mellitus.
 Hypertension
 Nephrolithiasis
 Drugs toxicity
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5. Kidney functions
Biological functions of kidney:
Excretion
Homeostatic regulation
And, Endocrine
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Types of Kidney
examination
Physical examination
Biochemical examination

6. Renal Function Tests / Biochemical examination
Can be classified broadly
into two categories:
1. Test that measures
glomerular function
2. Test that measures
tubular function
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Tests that are part of
kidney function test:
Urine examination
Serum urea
Serum Creatinine
BUN
Calcium, phosphorous, protein,
albumin

7. Renal Function Tests
Glomerular
Filtration Tests
Clearance test
Creatinine clearance
Urea clearance
Inulin clearance
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Dilution and
concentration test
Serum electrolyte
level

8. Routine Tests for Renal Functions
 Estimation of serum urea, creatinine.
 Determination of BUN.
 Estimation of serum electrolyte (Na, K).
 Estimation of serum total proteins/albumin.
 Urine analysis.
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9. Classification of Renal Function Test
Tests based on glomerulus filtration
Urea clearance, endogenous creatinine clearance test, inulin
clearance
Test to measure renal plasma flow
Tests based on tubular function
Certain miscellaneous tests
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10. Glomerular Filtration Test
What is meant by clearance test?
1. Urea Clearance Test
… expression of the number of ml of blood or plasma which are
completely cleared of urea by the kidney per minute.
Maximum clearance: when urine output is 2 ml/min.
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𝑼 × 𝑽
𝑷
U = concentration of urea in urine (in mg/dL)
V = Volume of urine in ml/min
B = Concentration of urea in blood (in mg/dL)

11. “
”
A urea clearance of 75 doesn’t mean that 75 ml of
blood has passed through kidney in one minute and was
completely cleared of urea. But, it means that the
amount of urea excreted in the urine in one minute is
equal to the amount found in 75 ml of blood.
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12. Interpretation of results
 Urea clearance of 70% indicates of normal functioning.
 In Acute Renal Failure: Urea clearance is usually less than ½.
 In Chronic Nephritis: Urea clearance falls progressively and
reaches to ½ or less of the normal before the blood urea concn.
Begins to rise.
 In Terminal Uraemia: Urea clearance falls to about 5% of the
normal value.
 In Nephrotic Syndrome: Urea clearance is usually normal until the
onset of renal insufficiency sets in and produces same change as
chronic nephritis.
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13. Interpretation of Urea clearance test results
(… in short)
1. If Urea clearance is >70%, renal function is normal.
2. If Urea clearance is between 40-70%, renal function is
mildly impaired.
3. If Urea clearance is <20%, renal function is severely
impaired.
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14. Endogenous Creatinine Clearance Test
(Procedure for Creatinine Clearance Test)
Collection of 24 hrs urine specimen.
Blood specimen is collected for serum creatinine estimation at
the mid point of 24 hrs urine collection.
The concentration of creatinine in both serum and urine is
measured.
Total urine volume is measured carefully.
Creatinine clearance is calculated.
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15. Calculation of creatinine clearance test
Ccr =
𝑼𝑽
𝑷
Corrected formula
Ccr =
𝑼𝑽
𝑷
× 𝟏. 𝟕𝟑 𝒎 𝟐/𝑨
Where, A: body surface area of the subject.
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16. Advantages of Creatinine Clearance Test
Endogenous metabolic product synthesized at a constant rate
for a given individual.
Unaffected by non-renal factors (e.g. protein diet, GI
hemorrhage)
Cleared essentially by glomerular filtration, not reabsorbed
and only slightly secreted (<5%) by PCT.
Its clearance value is closer to GFR.
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17. Staging of kidney disease based on GFR
values
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Stage Description GFR
(ml/min/1.73 m2)
1 Normal kidney function (but
urinalysis, structural abnormalities or
genetic abnormalities may indicate
renal disease)
≥90
2 Mildly reduced renal function 60-89
3 Moderately reduced renal function 30-59
4 Severely reduced renal function 15-29
5 End stage renal failure <15

18. Estimated GFR (eGFR)
 This calculation doesn’t require a timed urine collection.
 It should be used more often than traditional creatinine clearance.
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GFR (ml/min/1.73 m2) =
𝟏𝟒𝟎−𝒂𝒈𝒆 𝒊𝒏 𝒚𝒓𝒔 × 𝑾𝒆𝒊𝒈𝒉𝒕 𝒌𝒈 × 𝟐.𝟏𝟐 × 𝑲
𝒔𝒆𝒓𝒖𝒎 𝒄𝒓𝒆𝒂𝒕𝒊𝒏𝒊𝒏𝒆
𝒎𝒈
𝒅𝑳
× 𝑩𝑺𝑨 (𝒎 𝟐
)
Cockroft-Gault Formula

19. Urea Clearance Test
 Filtered at glomeruli.
 40-60% is reabsorbed by renal tubules.
 Clearance value less than normal GFR.
 Urea clearance is also influenced by non-renal factors like protein
content of diet, hypercatabolic state, urinary stasis, GI bleeding,
severe liver disease.
 Not in use.
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20. Inulin Clearance Test
Neither reabsorbed nor secreted by renal tubules.
Inulin clearance value is equal to GFR.
Administered intravenously to measure GFR.
Not in practice.
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21. Test to Measure Tubular Functions
Urine concentration test.
Determines the concentration ability of renal tubules.
Procedure
 No food or water after meal at 6 PM.
 Next day at 7 AM, collect urine and discard it.
 At 8 AM, collect urine specimen.
 Measure the osmolality of urine.
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22. Interpretation
Urine osmolality >850 mOsm/kg water (renal
concentration ability normal).
Lower osmolality of urine indicates
Chronic renal failure
Acute tubular necrosis
Nephrogenic diabetes insipidus etc.
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23. Measurement of Urine & Plasma
Osmolality Ratio
Ratio between urine osmolality and plasma osmolality is
1:1 – 3:1 (Normal condition).
Low ratio indicates renal tubular dysfunction.
In Diabetes insipidus, the ratio of 0.2:1 – 0.7:1.
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24. PSP Excretion Test
This test measures tubular activity as well as renal blood
flow.
Excretion of less than 23% of the dye during this period
regardless of the amount excreted in 2 hours indicates
impaired renal function.
It is also used to determine the function of both kidneys
separately.
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26. Biochemical changes in plasma in renal
failure
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Increased Decreased
Potassium Sodium
Urea Bicarbonate
Creatinine Calcium
Hydrogen ions
Phosphate
Magnesium

27. Markers Used for Clearance Tests
Exogenous markers
Inulin
51Cr-labelled EDTA
91Tec-Labelled EDTA
125I-iodothalamate
Iohexol
Idoacetate
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Endogenous markers
Urea
Creatinine
b2-Microglobulin
Retinol Binding Protein
a1-Microglobulin
Cystatin C

28. References
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