functions of kidney and the various tests to assess them

1. Excretion of urea and other metabolic wastes
Maintaining water, electrolytes and acid base balance
Retention of substances vital to the body
Activation of vitamin D
Production of Erythropoietin
Production of renin
Nephron is the functional unit of kidney
-glomeruli and tubules
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2. 3

3. Based on functions
a) Tests measuring GFR
b) Tests to study tubular function
Based on clinical application
Routine
a) Complete urine analysis
b) Measurement of NPN in blood
c) Measurement of Serum electrolytes
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4.  Measurement of GFR
 - clearance tests
 Markers of glucose permeability
 - proteinuria
 Measurement of tubular function
 Urine and plasma osmoality
 Concentration and dilution tests
 Tests to assess renal acidification
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5.  excretes metabolic waste products such as urea,
creatinine and uric acid
 maintains water and electrolyte balance with the
help of anti diuretic hormone and renin –
angiotensin – aldosterone mechanism
 maintains acid base balance by reabsorbion of
sodium as NaHCO3 in exchange for potassium
and hydrogen ion
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6.  It produces erythropoietin which helps in
promoting erythropoiesis in bone marrow
 play vital role in calcium metabolism
 helps to maintain serum calcium level with
the help of parathormone and vitamin D.
Renal enzymes 1alpha-hydroxylase converts
25-hydroxy cholecalciferol to 1,25 dihydroxy
cholecalciferol (calcitriol) which promotes
intestinal calcium absorption.
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7. Urine – volume
 When it is unusually more than 2500 ml / 24
hours it is called polyuria. It can be due to
 Increase in water loss
 Increase in solute excretion causing osmotic
water loss
 Increase in water loss due to either diminished
tubular dysfunction with decreased concentration
ability or ADH deficiency. ADH deficiency results
in diabetes insipidus. In this case urine specific
gravity will be lowered
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8.  In case of diabetic mellitus, there will be polyuria
due to glycosuria. In this case urine specific
gravity will be increased
 When urine output is less then 400 ml / 24 hrs, it
is called oliguria. If no urine is passed, then it is
called anuria
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9. Diminished performance of kidney is due to
 Renal diseases such as
 acute glomerulonephritis, tubular necrosis
etc.,
 Obstruction to the urine outflow
 e.g. tumour in the bladder, renal stones
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10. Diminished perfusion can be due to
 Diminished blood volume (eg. Dehydration)
 Diminished blood flow (eg. Cardiac failure)
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11.  Normally it is pale yellow or amber
colour
 Hematuria or hemoglobinuria produce a
dark brown colour.
 Reddish due to drugs
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Colour of the urine

12. pH of urine
 usually acidic pH 5.5-7.5
specific gravity
 normally varies from 1.016 – 1.025
 osmolality – 60-1200mosm/kg
 Odour – No odour
 foul smell indicates bacterial infection
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13.  detectable amount of protein in urine
indicates glomerular leak and is the first sign
of glomerular injury
 Normally the urinary excretion of albumin is
less than 30 mg/ 24 hrs. when the excretion
is between 30-299 mg/24 hrs, it is called
microalbuminuria.
 If it is more than 300 mg/24 hrs, it is called
macroalbuminuria. In case of severe damage
to glomeruli hematuira occurs.
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14. 15

15. Renal Clearance Test
 The renal clearance of a substance is
defined as the volume of plasma from
which the substance is completely cleared
by the kidneys per minute.
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16. Creatinine clearance test – is based on the rate
of excretion of creatinine, at a steady level.
For this test, 24 hr or 5 hr urine is collected.
Volume of urine, the urinary creatinine and
the plasma creatinine concentration are
measured.
 Creatinine clearance in ml/min
CCr = UV/P
 U= concentration of creatinine in urine
(mg/dl)
 P = plasma creatinine concentration (mg/dl)
 V = volume of urine passed per minute
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17. Normal value
 Men : 75-125 ml/dl
 Women : 65-115 ml/dl
 It is decreased in renal dysfunction and
indicates decreased glomerular filtration rate
 Clearance test is useful in the early stages of
renal disease where blood urea, serum
creatinine are elevated. That condition is
known as azotemia or uremia
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18. Creatinine is an endogenous product
Not varies with diet and only10% is
secreted by the tubules
Early detection
upto 75% of CCr - N function of kidneys
Cockcroft-Gault equation can be used
CCr = (140-age in yrs) xwt in kg(0.85
in females) x PCr in mg/dl.
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19.  Urea varies with protein diet and 40%
reabsorbed.
 So urea clearance < GFR
 No. of ml of blood which contains urea excreted
in a minute by the kidneys
 Calculation U x V/P
 U – mg urea /100 ml of urine
 V – ml of urine / mt
 P – mg urea / 100 ml plasma
 Normal Value – 75 ml/mt
 < 75% of N – Renal dysfunction
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20. 21

21. 22

22.  Specific gravity of urine
 Osmolality of urine is more valid than sp. gravity
 In Proteinuria sp. Gravity is elevated.
 Serum osmolality 285-300 mosm/kg
 Random urine osmolality - 600 mosm/kg
 Diabetes insipidus urine osmolality - 300
mosm/kg.
 ratio of urine/ serum osmolality 3-4.5
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23. Urine concentration (or) fluid deprivation test
After 15 hrs of withholding fluid intake the
first urine is discarded
a second specimen is collected
osmolality more than 850 mosm/kg
or specific gravity more than 1.022 indicates
normal renal function.
In renal failure urine specific gravity is fixed
at 1.010.
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24. 25

25.  Dilution test
 After overnight fluid restriction bladder is
emptied and a waterload of 1200 ml is
given.
 Osmolality fall to 50 mosm/kg
 or specific gravity to 1.003 indicates normal
renal function.
 Urine specimens are collected hourly for
next four hours
 In renal tubular disease, there will be a
fixed specific gravity
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26. Blood investigation
 Blood urea
 Serum creatinine
 Serum uric acid
 Na+
 K+
 Cl-
 HCO3
 PH
 PCO2
 PO2
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27. Urine investigation
 Protein
 Blood
 Sugar
 pH
 Specific gravity
 Creatinine clearance
 Osmolality
 Ca+
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28. It is indicated in hypercholeremic acidosis
Due to tubular defects or defects in ion pumps
Ammonium chloride 0.1 g / kg body weight
NH4 Cl NH4+Cl- NH4 Urea
Cl-+ H+ HCl
Urine sample collected hourly from 2 – 8 hrs
In one sample PH – 5.3
NH4 - 30 – 80 millimole /hr
CRF –pH may be low, NH3 excretion less
RTA - pH 5.3 is not achieved.
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30. Fractional excretion of HCo3
urine HCo3 x plasma creatinine x 100
= --------------------------
Plasma Hco3 x urine creatinine
Normal < 15%
> 20% - Type 2 (Proximal) RTA
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31. Fractional excretion of Po4
∆ of hypophosphatamia eg. X linked
hypophosphotamic rickets
Tubular maximum phosphate / GFR
Normal range 0.80 – 1.35 mmol/L
Tmp/CFR = TRP x plasma P if TRP is < 0.86
if TRP is > 0.86 TMP/GFR=0.30xTRP (1-
(0.8xTRP)] x plasma Po4
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32. Children & infants – high range
Decreased in x-linked hypophosphatemic
rickets
osteogenic osteomalaia
(failure of inactivation of phosphatonin- a
phosphauric hormone)
hyperparathyroidism
Increase d in hypoparathyroidism
Reduced phosphate reabsorption in
hypercalciuric stone, renal tubular
dysfunction
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