Renal function tests are very useful for effective clinical evaluation of renal failure for effective management. So it is useful for medical and allied professional students and clinical practitioners.
5. Kidney Synthesizes erythropoietin
which stimulates erythropoiesis.
Activation of 25-OH cholecalciferol
to 1,25 dihydroxy cholecalciferol
(Calcitriol) by 1-alpha hydroxylase
enzyme in the kidney which
promotes calcium absorption in the
6. Nephron is the functional unit of kidney which
has two components :
Glomerulus is the filtration unit and tubules
are reabsorbing unit.
7. Through Bowman’s capsule, an ultra-filtrate
which is devoid of cells and protein formed
Albumin does not pass through the membrane.
So in case of glomerular damage, albumin
appears in urine.
Glomerular filtration depends on renal blood
supply and functional state of nephrons.
8. Glomerular filtration rate (GFR) is :
1. Decreased in hemorrhagic shock, anaphylactic
shock due to decreased perfusion
2. In glomerulonephritis due to dysfunction of
Decrease in GFR leads to retention and
accumulation of waste products such as urea,
creatinine and uric acid in the plasma.
9. Plasma creatinine: Normal level is 0.6-1.2
It is a better indicator of GFR as it is not
influenced by diet or protein catabolism as in
case of urea.
It is inversely related to GFR.
Plasma urea : Normal plasma urea level is 15-
Plasma urea nitrogen is 7-18 mg/dl.
10. PAH is filtered at the glomerulus as well as
secreted by the tubules
Completely removed by the kidney by
single passage of blood through the kidney
Renal perfusion flow(RBF)= Upah/ppah x V
V= volume of urine (ml/min)
normal – 600 ml min
12. It is also an index of GFR.
Pre renal failure - dehydration.
urea is increased more than
creatinine because it is reabsorbed
by the tubular cells.
In renal failure, both will increase.
Post renal uremia-both will increase
13. Clearance is defined as the
volume of blood or plasma in ml
that is completely cleared of a
substance (in case of creatinine
clearance creatinine is cleared)
per unit time and is expressed as
ml per min.
14. Creatinine clearance = UV/P
U=concentration of creatinine in urine (mg/dl)
P=concentration of creatinine in plasma
V- volume of urine passed per minute
24 hours urine is collected and the total volume
is divided by 1440 .
15. Inulin clearance : It is the reference method for
determination of GFR. It is not routinely done
because it is given exogenously and the
maintenance of its blood level requires
It is lower than inulin clearance because urea is
reabsorbed in the tubules.
16. Marker should be freely filtered
It should be neither secreted nor reabsorbed
and it’s blood level should be constant.
Creatinine being an endogenous substance its
level is maintained, freely filtered but a small
amount is secreted by the tubules (10% of
creatinine excreted is tubular component).
17. Normal level is 0.5-1.0 mg/L.
Cystatin C is produced at a constant rate and is
freely filtered by glomerulus.
It is completely reabsorbed by the tubules and
degraded in the tubules.
The blood level is not dependent upon age, sex,
muscle mass or inflammatory processes.
It is a better indicator of GFR than creatinine
Extremely sensitive to minor changes in GFR
during the course of chronic kidney disease.
18. Normal value: male: 75-125 ml/min
Female: 65-115 ml/min
Decreased creatinine clearance is a very
sensitive indicator of reduced glomerular
filtration rate (GFR).
In old age, the clearance is decreased.
It is helpful in the early detection of functional
impairment of kidney and also for monitoring
the patients with renal insufficiency.
19. GFR mL/minute = [(140 – age in
years) × (wt, kg)]/ 72 × P (mg/L) ×
0.85 (if subject is female).
If converting to SI units (GFR in
micromoles per liter) is desired,
replace 72 in the denominator with
20. GFR (mL/minute/(1.73 m2)) = 186
× (serum creatinine [mg/dL]–1.154)
× (age in years)-0.203 × (0.742 if
female) × (1.210 if
If converting to SI units (GFR in
micromoles per liter) is desired,
replace 186 with 32,788.
21. Estimates GFR adjusted for body surface
Designed for use with laboratory
Is more accurate than creatinine clearance
measured from 24-hour urine collections
or estimated by the Cockcroft-Gault
23. The glomerular membrane is impermeable to
Low molecular proteins are filtered reabsorbed
and catabolized by tubular cells.
Albumin excretion is less than 30 mg/24 hours.
Urine test for albumin is negative in normal
24. It may be due to
1.Increase in filtered load due to glomerular
damage and vascular permeability. It is called
2.Increased concentration of low molecular weight
proteins in circulation resulting in Overflow
3.Decrease in the tubular reabsorption of proteins
resulting in tubular proteinuria.
25. Early morning urine specimen or 24hrs
urine specimen tested for albumin.
Benign proteinuria- 300mg/day
Pathological proteinuria- 300-1000
Glomerular proteinuria - > 1 gm/day.
In nephrotic syndrome massive
proteinuria is seen >3 gm/day.
26. If albumin is detected in a urine sample collected
at random, over 4 hours, or overnight, the test may
be repeated and/or confirmed with urine that is
collected over a 24-hour period (24-hour urine).
The quantity of albumin in urine is 30-300 mg/day
in micro albuminuria.
It is an early indication of nephropathy in diabetic
patients and hypertensive patients.
It is also expressed as albumin creatinine ratio
Albumin creatinine ratio – 30-300mg albumin /gm
of creatinine -0.03- 0.3
27. Over flow proteinuria
Hemoglobinuria in hemolytic diseases
Myoglobinuria in muscle crush injury
Bence- Jones protein in multiple myeloma
Due to decreased functional nephrons the
remaining nephrons over-work .
Tubular reabsorption of proteins is
impaired causing tubular proteinuria.
Proximal renal tubular damage -increased
excretion of β- microglobulin.
28. Urine specific gravity
Normal value is 1.016-1.022
Fixed specific gravity at 1.010 is seen in chronic
kidney disease due to tubular dysfunction.
Specific gravity is increased in diabetes
mellitus, adrenal insufficiency
Specific gravity is decreased in diabetes
insipidus (ADH insufficiency).
29. Normal range is 400-850 mOsm/kg
Plasma osmolality is 285-295 mOsm/kg.
Normally the urine- plasma osmolality ratio is
Urine osmolality - decreased in diabetes insipidus
and the ratio is lesser than 1.
Concentrating ability of distal tubules and
collecting ducts decreased.
Due to renal defect (nephrogenic diabetes
insipidus which do not response to ADH )
Central diabetes insipidus due to ADH deficiency.
31. For the test, patient should stop taking any fluid for
8 hours (Caution - dehydration).
In normal subjects urine osmolality will be more
than 800 mOsm/kg, plasma osmolality should not
exceed 295 mOsm/kg and the ratio will be more
In diabetes insipidus, the ratio is below 1 (0.2-0.7).
water deprivation with ADH stimulation, urine
osmolality - more than 800mOsm/kg - central
D.Insipidus but in nephrogenic diabetes
insipidus,less than 300mOsm/kg.
32. Urine dilution test
The patient is not allowed to drink any
fluid after mid night.
Bladder is emptied at 7 am and water load
(1200 ml over the next 30 min) is given.
Hourly urine samples are collected for
next four hours.
The specific gravity of at least one sample
should fall to 1.003 and osmolality to 50
This test is more sensitive and less harmful
than concentration test.
33. Enteric coated capsules containing ammonium
chloride at a dose of 0.1 g / kg body wt is given.
In the liver, NH3 is converted to urea and HCl is
produced which is excreted by kidney.
Urine is collected hourly from 2 to 8 hours after
At least one sample should have a pH of 5.3 .
In type I distal renal tubular acidosis, urinary pH
rarely falls below 6 and never falls below 5.3.
34. Phenolsulfonthalein test dye 6 mg in 1 ml
saline is given intravenously and urine samples
are collected at 15, 30, 60, 120 minutes.
If 15 minute urine contains 25% or more, the
test is normal.
If it is less than 23%, it indicates impaired
renal excretory function.
Normally 40-60% in 1 hour and 20-25% in the
second hour excreted.
35. More than 2500 ml / 24 hours it is called polyuria.
It can be due to : 1. Increase in water loss due to
either diminished tubular dysfunction with
decreased concentration ability or Anti diuretic
hormone deficiency. In ADH deficiency ( diabetes
insipidus), Urine specific gravity will be lowered
2. Due to excessive solute loss and osmotic diuresis -
In case of diabetic mellitus due to glucosuria, there
will be polyuria. In this case urine specific gravity
will be increased
36. Color of the urine
Normally it is pale yellow or
Hematuria or hemoglobinuria
produce a dark brown color.
By microscopy, hematuria can be
detected by the presence of
intact red blood cells.
It can be due to stone, tumor,
37. pH of urine
usually acidic- pH 6 (4.5-8-pH )
normally varies from 1.016 to
On average fluid intake, 300-900
Odor foul smell indicates
38. When urine output is lesser then 400 ml /
24 hours, it is called oliguria. If no urine is
passed, then, it is called anuria.
Oliguria, anuria can be the result of
Diminished perfusion of kidney ( cardiac
failure, Hypotension, shock),
Renal disease such as acute
glomerulonephritis, tubular necrosis,
Obstruction to the outflow e.g. bilateral
tumor in the bladder, renal stones,
prostate enlargement etc.
39. Urine investigations
Protein , Blood , Sugar, pH ,
specific gravity, osmolality,
Blood urea – 15 – 40 mg/dl
Serum creatinine – 0.6 – 1.2
Serum uric acid - 4- 7 mg/dl in
men , 3-6 mg/dL in women
44. A daily phosphate excretion of <3.2 mmol (100 mg)
and a fractional excretion of phosphate <5% (normal
value is 15–20%) allow diagnosis of non-
renal phosphate loss.
A urinary phosphate excretion >3.2 mmol (100 mg) or
a fractional excretion >5% is indicative of renal
Fractional excretion of phosphate (FeP) is associated
with end-stage renal disease patients with CKD 3b
FGF23 (Phosphotonin)is secreted from bones and acts
on the kidneys to induce phosphaturia and suppress
active vitamin D synthesis
It maintain phosphate homeostasis.
45. Decreased in X-linked hypophosphatemic
Osteogenic osteomalaia - (failure of
inactivation of phosphatonin)
Increased in hypoparathyroidism
Reduced phosphate reabsorption in
hypercalciuric stone, renal tubular dysfunction
46. Metabolized in tubules
Urinary measurement of beta 2
microglobulin provide a sensitive index
of assessing tubular integrity
beta2 microglobulin in urine is
In serum or plasma samples is
47. Fractional excretion of Na
= Urine Na / serum Na x 100
Urine creatinine / Sr.creatinine
< 1% in prerenal azotemia
> 1.5% in acute tubular necrosis
> 3% in postrenal failure
48. RFI (mmol/L) =
Urine Na x serum creatinine
/ urine creatinine
Prerenal failure < 1 mmol/L
Post renal failure and nephrotoxic
renal failure > 3 mmol/L
49. Urea , creatinine , uric acid , creatinine
clearance, eGFR, cystatin
Sodium, potassium, bicarbonate, chloride
Serum albumin ,total protein
CBC and Urinalysis
Urine albumin creatinine ratio
Sr. AST, ALT ALP, bilirubin