1. RENAL FUNCTION TEST

2. INTRODUCTION
 The kidneys are two bean shaped organs lying on each side of the vertebral column slightly above the
level of umbilicus.
 Each kidney contains approx. 1 million nephrons.
 A Nephron consist :-
 OUTER LAYER
(the cortex)
-glomeruli
-PCT & DCT
-CD
 INNER LAYER
(the medulla)
-Straight portion of tubules
-LOH
-vasa recta
-terminal CD

3. FUNCTIONS OF KIDNEY
 Formation of urine as the waste product
 Excretion of end products of protien and nucleic acid metabolic substances
 Regulation of salt & water balance
 Regulation of acid-base balance
 Production of Hormones

4. Why test renal function?
 To asses the functional capacity of kidney.
 Early detection of possible renal impairment.
 Severity and progression of the impairment.
 Monitor response to treatment.
 Monitor the safe and effective use of drugs which are excreted in the
urine

5. When should we assess renal function?
 Older age
 Family history of Chronic Kidney disease (CKD)
 Decreased renal mass
 Low birth weight
 Diabetes Mellitus (DM)
 Hypertension (HTN)
 Autoimmune disease
 Systemic infections
 Urinary tract infections (UTI)
 Nephrolithiasis
 Obstruction to the lower urinary tract
 Drug toxicity

6. MACROSCOPIC EXAMINATION
 Color
Normal-pale yellow in color due to pigments urochrome,urobilin, Cloudiness may be caused
by excessive cellular material or protein, crystallization or precipitation of salts upon standing at
room temperature or in the refrigerator.
If the sample contains many red blood cells, it would be cloudy as well as red.
Normal Deep yellow---- conc. Of urochrome pigment
Red Blood, Hemoglobulinuria, myoglobinuria, beetroot
Orange rifampicin
Yellow Concentrated urine, ( dehydration, jaundice, B complex, sulfasalazine)
Green Methylene blue
Black Severe hemoglobinuria, methyldopa
Brown Bilirubin, phenothiazides

7.  VOLUME
Normal- 800 ml -2.5 L/day
 Oliguria- Urine Output < 300ml/day
Seen in
 Acute glomerulonephritis
 Renal Failure
 Polyuria- Urine Output > 2.5 L/day
Seen in
 Increased water ingestion
 Diabetes mellitus and insipidus.
 Anuria- Urine output < 100ml/day
Seen in renal shut down

8.  Specific Gravity
 Normal ranges 1.002 – 1.025
 Varies with quantity of urine
Low SG
 CRF
 diabetes insipidus
 Absence of ADH
 Renal tubular demage
High SG
 Dehydration
 diabetes mellitus
 Albuminuruia
 Acute nephritis

9.  pH
 Urine pH ranges from 4.5 to 8
 Normally it is slightly acidic lying between 6 – 6.5.
 After meal it becomes alkaline.
 On exposure to atmosphere, urea in urine splits causing NH4
+ release
resulting in alkaline reaction.

10.  1. Urine analysis
 2. Tests for assessment of glomerular function
 3. Tests to measure renal plasma flow
 4. Tests for assessment of tubular function

11. 1. Urine Analysis
 Urine examination is an extremely valuable and most easily performed
test for the evaluation of renal functions.
 It includes physical or macroscopic examination, chemical examination
and microscopic examination of the sediment.

12. 2. TEST FOR ASSESSMENT OF GLOMERULAR FILTERATION
 Clearance test
Creatinine clearance
Urea clearance
Inulin clearance
 Dilution and concentration test
 Serum electrolyte level

13. 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.
𝑼×𝑽𝑷
U = concentration of urea in urine (in mg/dL)
V = Volume of urine in ml/min
P = Concentration of urea in blood (in mg/dL)
 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.

14. Interpretation of results for urea clearance
 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 conc. 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.
 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.

15. 2.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.

16. Calculation of creatinine clearance test
 Ccr= 𝑼 𝑽
P
Corrected formula
 Ccr= 𝑼 𝑽 × 𝟏.𝟕𝟑𝒎𝟐/𝑨
P
Where, A: body surface area of the subject.

17. Staging of kidney disease based on GFR values
STAGE DESCRIPTION GFR
(ml/min/1.73m2)
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. 3. 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.

19. 3. Tests to measure renal plasma flow
i. Para-amino hippurate (PAH)
 PAH is filtered at glomeruli & secreted by the tubules.
 PAH is completely removed during a single blood circulation through kidneys
at low blood conc.(2mg or less/100ml) of plasma.
 PAH clearance at low blood levels measures renal plasma flow (RPF).
RPF= 574ml/min

20. ii) Filtration Fraction(FF)
 Filtration fraction is the fraction of plasma passing through the kidneys which
is filtered at the glomerulus and is obtained by dividing the Inulin clearance by
PAH clearance.
 NORMAL RANGE:- 0.16 to 0.21 in an adult.
 FF= CIM = GFR
CPAH RPF

21. 4. Test to Measure Tubular Functions
A. Urine concentration test.
Determines the concentration ability of renal tubules.
 Procedure
1. No food or water after meal at 6 PM.
2. Next day at 7 AM, collect urine and discard it.
3. 3At 8 AM, collect urine specimen.
4. Measure the osmolality of urine
 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.

22. B. 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.

23. C. Urine Dilution
 Urine dilution test is done to assess the ability of kidneys to eliminate water.
 This function is tested by measuring urinary output after ingesting a large volume of
water.
 This test is not advisable for patients with adrenal insufficiency

24. D. Urine Acidification
 Urine acidification test is done to check the ability of kidney toproduce acidic urine
which is the function of tubules.
 For this test, patient is asked to empty the bladder.
 The pH of urine is measured which should be between 4.6 to 5.0.
 In patients with RENAL TUBULAR ACIDOSIS , pH does not fall below 5.3 even after
dose of ammonium chloride