Renal function test for Medical, Paramedical and Allied Health sciences students

1. RENAL FUNCTIONAL
TESTS
By
Dr. Santhosh Kumar N
Associate Professor
Department of Biochemistry

2. RENAL FUNCTIONS
Excretory functions
To eliminate non-volatile
waste metabolites from blood
Absorption of useful solutes
by tubule cells
Homeostatic function
Maintaining Water & electrolytes
balance –regulate blood volume & BP
Regulation of acid-base Balance
(Body pH )
Endocrine function
Production of hormones -
Erythropoietin, Renin & Calcitriol
Main line of defense against
acidosis & alkalosis
Renal medulla is also a site for
gluconeogenesis

3. Endocrine function of kidneys
Macula densa
(Juxtaglomerular cells)
acts as a sensor of the Na+
levels in the tubular fluid
Low Na+ levels produced
renin
leads to the production
of angiotensin-II &
Aldosterone.
Interstitial cells in the
peritubular capillary
bed of the kidneys
Produce erythropoietin
in response of hypoxia
act as stem cells in the
bone marrow to increase
the RBC production
Activation of
Vit-D
(calcitriol).
1,25-DHC
Inactivated
25-OH
cholecalciferol to
24, 25- dihydroxy
cholecalciferol by
24-hydroxylase

4. – Renal blood flow
– Glomerular filtration rate
– Renal glomeruli function
– Renal tubular functions and
– Urinary output
To assess the glomerular function & integrity, and tests to identify the underlying
cause of the renal disease.
RFTs give information regarding

5. RENAL FUNCTION TEST
(To screen for kidney disease )
To screen for
kidney disease
To assess renal functions
Based on glomerular
filtration
Measure RPF
(renal plasma flow)
Based on Tubular functions
Complete urine
analysis
Estimation of
blood urea &
serum creatinine
& S.Electrolytes
a) Urea clearance
test
b) Creatinine
clearance test
c) Inulin clearance
test
d) Cystatin-C
-PAH (Para- mino
Hippurate) Test
- Filtration
Fraction
a) Concentration tests
b) Dilution tests
c) PSP excretion test
d) Renal acidification

6. Tests to identify the etiology of renal diseases
 Complete urine analysis
• Physical characteristics- volume, color, odor, appearance sp.gravity and pH
• Chemical characteristics –checking for the presence of Protein &, blood in urine
 Estimation of blood urea & serum creatinine
 Estimate the serum electrolytes by ISE method

7. GFR cannot be measured directly , it is estimated from the clearance of filtration markers
Creatinine Clearance Test:
 Volume of plasma that would be completely cleared of creatinine in 1min
 It is close to the GFR
 It is helpful to assess the renal glomerular function.
Estimation of Glomerular Filtration Rate (GFR)

8. U=Urine creatinine conc. in mg /dl
V= Volume of urine excreted per min
(ml/ min)
P= Plasma creatinine in mg/dl
Biological reference values
• Males: 85-125ml/min
• Females: 80 -118ml/min

9. Advantages of creatinine clearance
– Endogenous product
– Not dependent on protein intake
– Neither absorbed nor secreted by renal tubules
– Early indicator of impairment of kidney function
Clinical significance of creatinine clearance :
• Increased : muscle dystrophy, hyper catabolic states & starvation
• Decreased : advanced renal failure

10. Creatinine coefficient
• It is more precise & is used to assess muscle mass of an individual
• To check the accuracy of 24hr urine sample collection
Creatinine coefficient = mg of creatinine in 24hr urine/ body weight (Kg)
Reference values:
Males :20 to 28 mg/kg/day
Females :15 to 21 mg/kg/day

11. Cystatin-C as a GF marker:
• Low mol wt protein(13kD) acting as cysteine protease inhibitor in the body
• Produced at a constant rate & freely filtered through glomeruli
• Completely reabsorbed by the tubules
• Reference blood: 0.8 to 1.2mg/L
– Unaffected by age, sex, muscle mass, diet & inflammatory process , unlike
creatinine
– It is a very good marker for estimation of GFR

12. Urea Clearance Test
• Volume of plasma that would be completely cleared of urea in 1 min
• 40% is reabsorbed by the tubules after filtration.
• Not useful for estimation of GFR, by itself
• Clearance is highly dependent on urine flow rate
• Hydrated state leads to high urine flow resulting in clearance of urea ˃70% of GFR
• In dehydrated state, urea may be ˂ 30%

13. U = conc. of urea in urine (mg/100ml)
V= volume of urine excreted per min ( ml/min)
B or P = the conc. of urea in blood (mg/dl)
*maximum urea clearance= 75 ml/min
*Urea clearance is lowed in acute renal failure & chronic nephritis

14. Inulin Clearance Test
100ml of sterile 10% solution of inulin is
given as slow IV drip within 2 hrs
Urine specimen formed during this period
is collected totally
Blood sample is taken at the middle of the
test.
Inulin is estimated by resorcinol giving a
red color

15. TESTS FOR
TUBULAR FUNCTION

16. Assessment of the concentration & diluting ability of the kidneys depends upon
• U. specific gravity & osmolarity used to measure the conc. & diluting ability of the tubules.
Adequate GFR
Presence of antidiuretic hormone
Healthy tubular cells
Tubular mass
Renal plasma flow

17. Urinary specific gravity
• Simplest test of tubular function
• Specific gravity depends on the concentration of solutes,
• Cases of Proteinuria the Sp.gravity is elevated

18. Measurement of Osmolality
• Osmolality depends on the no. of osmotically active particles.
• Measured with an osmometer (based on the depression of the freezing point of the
sample)
• Normal urine osmolality : 60 to 1200 mOsm/Kg
Plasma osmolality: 285 to 300 mOsm/Kg
• Measurement of plasma /urine osmolality is more helpful (Normal ratio of
osmolality plasma /urine is from 3 to 4.5)

19. Urine Concentration test
Patient is allowed no food or water
after a meal at 6pm
Next day at 7am, the bladder is
emptied and specimen is discarded
A second specimen is collected at 8am
and the sp.gravity is measured
If the sp.gravity is more than 1.018 (Osmolality
should exceed 750mOsm/kg) patient has adequate
renal function
-The urine sp.gravity is around 1.010 (300mOsm/kg)
–isosthenuria
-Increased excretion of urine at night is an early
indication of tubular dysfunction

20. Urine dilution test
Patient is not allowed no drink water after
midnight
Next day at 7am, the bladder is emptied
and more water load is given (1.2L
over the next 30min)
Hourly urine samples are collected for the
next 4hrs separately.
Volume, sp.gravity and osmolality of
each sample are measured
-It is more sensitive and less harmful then
concentration test
Normal Renal functions –
- more than 80% of water is voided within 4hr.
- 1.005 or less Sp.gravity and 50mOsm/kg
Osmolality

21. • Impaired Renal functions
- less than 80% of water is excreted in 4hr and Specific gravity is 1.010.
- Dehydration
- Tubular defect
- Decreased secretion of ADH (Polyuria of diabetes insipidus)

22. Phenol sulphthalein (PSP) excretion test
• PSP test measures Primarily tubular activity & renal blood flow.
15-min PSP test:
• Sensitive test.
• The amount of dye excreted in the first 15 min is taken as the measure of renal function.
• When 6mg of PSP in 1ml of saline is injected IV, normal kidneys will excretes 30 to 50 %
of the PSP dye during the first 15min.
• Excretion of PSP less than 25%, it indicates impaired renal function.

23. Acid load test (urine acidification test) /ammonium chloride
loading test
• Occasionally used for the diagnosis of renal tubular acidosis
• 100mg of Ammonium chloride /kg b.wt is administered orally in gelatin capsule to cause
metabolic acidosis
• The capacity of the kidneys is assessed for the production of acidic urine
• Urine samples are collected hourly for the following 8hr

24. Clinical interpretation
• In normal: the urine pH is falls below 5.5 in at least one sample (5.5 to 7.5)
• Renal tubular acidosis – decrease does not occur, which remains between 5.7 to 7
Metabolic acidosis arises due to diminished tubular secretion of H+ ions

25. Case report - 01
A 6 year old boy was brought to paediatric OPD by mother with complaints of
puffiness of face, generalized swelling of body with decreased urine output. His lab
investigations revealed
Report Normal Ranges
Blood urea: 55 mg/dl (15-45 mg/dl)
Serum creatinine: 1.6 mg/dl (0.7-1.4 mg/dl)
Serum total protein: 5.0 g/dl (6-8 gm/dl)
Serum albumin: 2.5 g/dl (3.5 – 5 gm/dl)
Serum cholesterol: 400 mg/dl (150-200mg/dl)
Urine albumin: + + + +
Urine blood: Negative
Q: a) What is the probable diagnosis?
b) What are the causes for this condition?
c)Explain the biochemical basis of hypercholesterolemia in the above condition
d) Explain the biochemical basis of generalized edema

26. a) What is the probable diagnosis?
Nephrotic syndrome
b) What are the causes for this condition?
- Kidney diseases such as nephropathy and focal glomerulosclerosis.
- Secondary causes: diabetes mellitus (diabetic nephropathy) and amyloidosis
c) Explain the biochemical basis of hypercholesterolemia in the above
condition
Loss of albumin in urine leads to increased synthesis of globulins to balance the
total proteins. Hence serum lipoproteins is excessively syntheised
d) Explain the biochemical basis of generalized edema
Loss of albumin in urine leads to decrease in effective osmotic /oncotic pressure
and decrease in return of water into the vessels and accumulation of water in
tissues leads to edema

27. Case report - 02
This is a laboratory report of patient. Comment on the report & write your
probable diagnosis.
Report Normal Ranges
Blood urea : 80 mg/dl (15-45 mg/dl)
Serum creatinine : 3.0 mg/dl (0.7-1.4 mg/dl)
Serum total protein : 5.5 g/dl (6-8 gm/dl)
Serum albumin : 3.5 g/dl (3.5–5 gm/dl)
Serum total cholesterol: 160.0 mg/dl (150-200mg/dl)
Urine albumin: + +
Urine blood : Positive
Q: a) What is the probable diagnosis?
b) How do you interpret this report?
c) What are the causes for this condition?

28. a) What is the probable diagnosis?
 Glomerulonephritis
b) How do you interpret this report
• Inflammation and subsequent damage of the glomeruli leading to hematuria, proteinuria,
and azotemia
• Other clinical features: pyuria (white blood cells present in urine), edema, oliguria & High
blood pressure (hypertension)
C) What are the causes for this condition?
 It is the third most common cause of end-stage renal disease & systemic conditions like
Diabetic kidney disease, hypertension & Lupus (A chronic inflammatory disease)
 Streptococal infection causing immune mediated injury to glomerular filtration membrane
leads to the damage of glomerular basement membrane.

29. “Your Greatest
Resource Is Your
Time”.
Next is TFTs