Renal function tests

1. Renal Function Tests
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
R.D. Gardi Medical College, Ujjain, Madhya Pradesh.
Email: dr.goothy@gmail.com

2. To asses functional
capacity of the kidney
To detect renal
impairment as early as
possible
Detect kidney disease
well before the
symptoms appear
Determine the etiology
of renal disease
RENAL
FUNCTION
TESTS

3. Classification of Renal Function Tests
 To screen for kidney disease
1. Complete urine analysis
2. Plasma urea and creatinine
3. Plasma electrolytes

4. Classification of Renal Function Tests
 To assess glomerular function
1. Glomerular filtration rate
2. Clearance tests
3. Glomerular permeability
4. Proteinuria

5. Classification of Renal Function Tests
 To assess tubular function
1. Reabsorption studies
2. Secretion tests
3. Concentration and dilution tests
4. Renal acidification

6. Physical characteristics of urine
 Volume
Urine out put is 1.5 lit/day
Urine volume may be increased in excess water intake, diuretic
therapy, diabetes mellitus, chronic renal diseases.
Urine volume may be decreased in excess sweating, dehydration,
edema, kidney damage.

7. Physical characteristics of urine
 Color
Pale yellow in color due to uribilinogen
Dark yellow color- Jaundice
Red- blood
White - Chyluria

8. Physical characteristics of urine
 Osmolality and specific gravity
Osmolality varies from 60-1200msomol/L
Specific gravity varies from 1.003- 1.030

9. Physical characteristics of urine
 Urinary pH
Varies from 4.5-8.0

10. Physical characteristics of urine
 Abnormal urinary constituents
Proteins, glucose, ketones, bilirubin, bile salts, blood etc. may
present depending on the disorder.

11. Physical characteristics of urine
 Microscopic examination
Casts, cells and crystals may be present in urine
RBC, WBC, and epithelial cells may present
Calcium oxalate, phosphate, uric acid, and cysteine crystals may
present

12. Physical characteristics of urine
 Bacteriological examination
Bacteria, pus cells may be present in urinary tract infections

13. Physical characteristics of urine
 urine output
normal1.5 lit/day
Oliguria <400ml/day
Anuria <100ml/day
Polyuria >3000ml/day

14. Physical characteristics of urine
 Urine output
Normal1.5 lit/day
Oliguria <400ml/day
Anuria <100ml/day
Polyuria >3000ml/day

15. Chemical characteristics of urine
 Reaction to litmus
pH of urine varies from 5.5-7.5
If a protein-rich diet is consumed, urine becomes more acidic due to
the production of sulfuric and phosphoric acids from amino acids.
If the diet is vegetable-rich, urine will be alkaline because the organic
acids in vegetables are converted to bicarbonate.

16. Chemical characteristics of urine
 Proteins
PROTEINURIA IS IMPORTANT INDEX OF RENAL DISEASE
Normal urine- protein concentration is very low and can not be
detected by usual tests.
Altered glomerular permeability causes filtration of proteins

17. Chemical characteristics of urine
 Blood
Hematuria is seen in nephritis and post renal hemorrhage
Hemoglobinuria is due to an abnormal amount of hemolysis
Hemastix strips are available for rapid testing of blood in urine

18. Chemical characteristics of urine
 Reducing sugars (Glycosuria)
Benedicts test is used for sugar estimation in urine
Diabetes mellitus

19. Chemical characteristics of urine
 Ketone bodies
Acetoacitic acid
Beta hydroxy butyric acid
Acetone
Ketonuria is seen in diabetes mellitus, starvation, persistent vomiting,
and alkalosis
Ketostix strips are available for rapid test of ketone bodies

20. Chemical characteristics of urine
 Bile salts
Present in urine during early phases of obstructive jaundice
Their presence is identified by Hay’s test

21. Chemical characteristics of urine
 Bile pigments
Bilirubin, Biliverdin
Present in urine during obstructive jaundice
Their presence is identified by Fouchet’s test

22. Chemical characteristics of urine
 Urobilinogen
Hepatocellular jaundice- urobilinogen is absent in urine
The earliest sign of recovery is the reappearance of urobilinogen
in urine
Their presence is identified by Ehrlich test

23. Chemical characteristics of urine
 Non protein nitrogen
Includes urea, creatinine and uric acid
In kidney dysfunction, these compounds concentration is
increased in plasma
Of the three creatinine estimation is most specific and sensitive
index of renal function

26. Markers of glomerular filtration rate
 Measurement of clearance is predominantly a test of GFR
Measurement of GFR provides information about the severity of
renal damage
Decrease in the renal function is due to loss of functional
nephrons
Normal GFR for young adults is 120-130 ml/min

27. Plasma clearance
 The plasma clearance of any substance is defined as the volume
of plasma completely cleared of that substance by the kidneys
per minute
It refers not to the amount of the substance removed but to the
volume of plasma from which that amount was removed.
Plasma clearance is actually a more useful measure than urine
excretion.

28. Plasma clearance
 it is more important to know what effect urine excretion has on
removing materials from body fluids than to know the volume and
composition of discarded urine.
Plasma clearance expresses the kidneys’ effectiveness in
removing various substances from the internal fluid environment.

30. Plasma clearance
 The plasma clearance rate varies for different substances,
depending on how the kidneys handle each substance.
Let us consider how three common patterns of renal handling
influence clearance rates for the involved substance.

31. Plasma Clearance Rate for a Substance Filtered But
Not Reabsorbed or Secreted
 No normally occurring chemical in the body has the characteristics of substance X.
All substances naturally present in the plasma, even wastes, are reabsorbed or
secreted to some extent.
However, inulin (do not confuse with insulin), a harmless foreign carbohydrate
produced abundantly is freely filtered and not reabsorbed or secreted—an ideal
substance X.
Inulin can be injected and its plasma clearance determined as a clinical means of
finding out the GFR.

34. Plasma Clearance Rate for a Substance Filtered But
Not Reabsorbed or Secreted
 Although determination of inulin plasma clearance is accurate and straightforward, it is not
very convenient because inulin must be infused continuously throughout the determination to
maintain a constant plasma concentration.
Therefore, the plasma clearance of an endogenous substance, creatinine, is often used
instead to find a rough estimate of the GFR.
 Creatinine, an end product of muscle metabolism, is produced at a relatively constant rate. It
is freely filtered and not reabsorbed but is slightly secreted.
Accordingly, creatinine clearance is not a completely accurate reflection of the GFR, but it
does provide a close approximation and can be more readily determined than inulin clearance.

35. Creatinine coefficient
 Urinary creatinine expressed in mg/kg body weight
The value elevated in muscular dystrophy
Normal range 20-28 mg/kg in males
15-21 mg/kg for females

36. Cystatin C as a filtration marker
 More advantages than serum creatinine
0.8-1.2 mg/L normal level
Excellent GFR marker
Blood levels are not dependent on age, sex, muscle mass or
inflammatory processes

37. Plasma Clearance Rate for a Substance Filtered and
Reabsorbed
 Some or all of a reabsorbable substance that has been filtered is returned to the
plasma.
The plasma clearance rate of a reabsorbable substance is always less than the GFR.
For example, the plasma clearance for glucose is normally zero. All the filtered glucose
is reabsorbed with the rest of the returning filtrate, so none of the plasma is cleared of
glucose.
 For a substance that is partially reabsorbed, such as urea, only part of the filtered
plasma is cleared of that substance. With about 50% of the filtered urea being passively
reabsorbed, only half of the filtered plasma, or 62.5 mL, is cleared of urea each minute

40. Clearance Rate for a Substance Filtered and Secreted
 Tubular secretion allows the kidneys to clear certain materials from
the plasma more efficiently.
 Only 20% of the plasma entering the kidneys is filtered. The
remaining 80% passes unfiltered into the peritubular capillaries.
The only means by which this unfiltered plasma can be cleared of
any substance during the trip through the kidneys before being
returned to the general circulation is by secretion.

41. Clearance Rate for a Substance Filtered and Secreted
 An example is H+.
Not only is filtered plasma cleared of nonabsorbable H+, but the
plasma from which H+ is secreted is also cleared of H+.
The plasma clearance rate for a secreted substance is always
greater than the GFR.

43. Clearance Rate for a Substance Filtered and Secreted
 Just as inulin can be used to determine the GFR, plasma clearance of another foreign
compound, the organic anion para-aminohippuric acid (PAH), can be used to measure
renal plasma flow.
Like inulin, PAH is freely filterable and nonreabsorbable.
It differs, however, in that all the PAH in the plasma that escapes filtration is secreted
from the peritubular capillaries by the organic anion secretory pathway in the proximal
tubule
The plasma clearance for PAH is a reasonable estimate of the rate of plasma flow
through the kidneys.

44. Clearance Rate for a Substance Filtered and Secreted
 Typically, renal plasma flow averages 625 mL/min, for a renal blood
flow (plasma plus blood cells) of 1140 mL/min—more than 20% of the
cardiac output.
If you know the rates of inulin clearance (GFR) and PAH clearance
(renal plasma flow) you can easily determine the filtration fraction,

46. Blood urea levels
 Normal serum urea is 20-40 mg/dl
 End product of protein metabolism
As age advances, serum concentration increases
Lower limit is normal for young adults
Upper limit is normal for elderly
Late pregnancy and in starvation the urea levels may decrease

47. Markers of glomerular permeability
 Glomerular proteinuria
 Plasma proteins are absent in normal urine
When glomeruli damages, they become more permeable and plasma
proteins appear in urine
Smaller molecules of albumin pass through
Albuminuria is pathological

48. Markers of glomerular permeability
300 mg/day = Benign proteinuria
300-1000 mg/day = pathological proteinuria
>1000 mg/day = glomerular proteinuria

49. Tests for tubular function
Specific gravity of urine
1.015-1.025
Decreased in excessive water intake, chronic nepohritis, diabetes
insipidus
Earliest manifestation of renal disease is difficulty in concentrating
the urine

50. Tests for tubular function
Osmolality of urine
60-1200 msomol/kg
A random urine sample has osmolality of 600 msomol/kg
After 12 hours of fluid restriction it increases to 850msomol/kg

51. Tests for tubular function
Concentration test
Measure specific gravity after 12 hours fast
If specific gravity is >1.022, patient has adequate renal function
In normal persons, specific gravity can be as high as 1.032
As disease progress, the urine specific gravity is fixed at 1.010

52. Tests for tubular function
Dilution test
Bladder is emptied at 7 am
Water load is given ( 1200ml over the next 30 minutes)
Hourly urine samples collected next 4 hours
Volume, specific gravity and osmolality measured
Normal person excrete all the water load within 4 hours
Specific gravity of atleast one sample should fall to 1.003
More sensitive test than concentration test

53. Tests for tubular function
Urine acidification test
Urine pH should be less than 5.4 after administration of 0.1g/kg body
weight of NH4Cl

54. Radiology and renal imaging
1. Plain radiograph of abdomen
2. Intravenous pyelograhy
3. Ultrasonography
4. CT
5. Radionuclide studies
6. MRI
7. PET

55. Renal biopsy
• Percutaneously using Vim Silverman needle