Organ function tests

Renal Function Test

An Introduction to the Urinary System
Anatomy of Nephron
 Kidney

 Urine excreted daily in adults: 1.5 L

 Kidney only 1% of total body weight.
 Reflects two processes
 Ultrafiltration (GFR): 180 L/day
 Reabsorption: >99% of the amount filtered
 The Function of Urinary System
A) Excretion & Elimination:
removal of organic wastes products
from body fluids (urea, creatinine,
uric acid, sulphates, phosphates)
B) Homeostatic regulation:
Water -Salt Balance
Acid - base Balance
C) Endocrine function:
Hormones- Renin, Erythropoietin &
Vitamin D3
 Renal threshold

 Renal threshold of a substance is the concentration in

blood beyond which it is excreted in urine.
 Renal threshold for glucose is 180 mg/dL

 Tubular maximum (Tm): maximum capacity of the

kidneys to absorb a particular substance.
 Tm for glucose is 350 mg/min
 Where can it break?

 Pre-renal- e.g. decreased intravascular volume

 Renal (intrarenal)- e.g. acute tubular necrosis

 Post-renal (obstruction)- e.g. ureteral obstruction

 Signs and Symptoms of Renal Failure

 Symptoms of Uremia (nausea, vomiting, lethargy)

 Disorders of Micturation (frequency, nocturia, dysuria)
 Disorders of Urine volume (polyuria, oliguria, anuria)
 Alterations in urine composition (haematuria, proteinuria,
bacteriuria, leukocytouria, calculi)
 Pain
 Oedema (hypoalbuminaemia, salt and water retention)
 Why Test Renal Function?

 To identify renal dysfunction.

 To diagnose renal disease.
 To monitor disease progress.
 To monitor response to treatment.
 To assess changes in function that may impact on
therapy (e.g. Digoxin, chemotherapy).
Biochemical Tests of Renal Function

1. Measurement of GFR
2. Renal tubular function tests
3. Urinalysis
Biochemical Tests of Renal Function

 Measurement of GFR
 Clearance tests ( Inulin, Creatinine & Urea)
 Plasma creatinine
 Urea, uric acid and β2-microglobulin, cystatin C
 1. Measurement of GFR
Clearance tests ( Inulin, Creatinine & Urea)

➢ Clearance is defined as the quantity of blood or plasma

completely clear of a substance per unit of time.

(U  V)
C=
P
 Measurement of GFR
Clearance tests ( Inulin, Creatinine & Urea)

➢Inulin
➢The Volume of blood from which inulin is cleared
or completely removed in one minute is known as
the inulin clearance and is equal to the GFR.

➢Measurement of inulin clearance requires the

infusion of inulin into the blood and is not suitable
for routine clinical use
 Creatinine
➢1 to 2% of muscle creatine spontaneously converts to
creatinine daily and released into body fluids at a
constant rate.
➢ Plasma levels (0.7-1.4 mg/dl)
➢Creatinine clearance may be measured as an
indicator of GFR.
 Creatinine clearance and clinical utility
➢The most frequently used clearance test.

➢ Small quantity of creatinine is reabsorbed by the

tubules and other quantities are actively secreted by the
renal tubules.

➢ Creatinine clearance is approximately 7% greater

than inulin clearance.
 Creatinine clearance and clinical utility
➢An estimate of the GFR can be calculated from the creatinine
content of a 24-hour urine collection, and the plasma concentration
within this period.
➢The volume of urine is measured, urine flow rate is calculated
(ml/min) and the assay for creatinine is performed on plasma and
urine to obtain the concentration in mg per dl or per ml.

➢Creatinine clearance in adults is normally about of 120 ml/min.

 Plasma Urea

Urea is the major nitrogen-containing metabolic

product of protein catabolism in humans,
✓Its elimination in the urine represents the major
route for nitrogen excretion.
✓More than 90% of urea is excreted through the
kidneys, with losses through the GIT and skin
✓Plasma urea concentration is often used as an
index of renal glomerular function
 Plasma Urea
✓Urea production is increased by a high protein
intake, and it is decreased in patients with a low
protein intake or in patients with liver disease.
✓Serum urea of healthy adults is 15-40 mg/dl.
✓Renal diseases with various glomerular, tubular,
interstitial or vascular damage can cause ↑ in
plasma urea concentration
 Plasma Urea
Clinical Significance

 Elevated levels of urea in blood are referred to

as uremia or azotemia.
 Causes of urea plasma elevations:
➢ Prerenal: renal hypoperfusion
➢ Renal: acute tubular necrosis

➢ Postrenal: obstruction of urinary flow

 Uric acid

➢In human, uric acid is the major product of the catabolism

of the purine

➢In humans, approximately 75% of uric acid excreted in the

urine; most of the reminder is secreted into the GIT.

➢Hyperuricemia is defined by serum or plasma uric

acid concentrations higher than 7.0 mg/dl in men
or greater than 6.0 mg/dl in women
 Plasma β2-microglobulin
➢β2-microglobulin is a small peptide (molecular weight
11.8 kDa),
➢It is present on the surface of cells and in low
concentrations in the plasma.
➢It is completely filtered by the glomeruli and is
reabsorbed and catabolized by proximal tubular cells.
➢The plasma concentration of β2-microglobulin is a good
index of GFR in normal people, being unaffected by diet or
muscle mass.
➢It is increased in certain malignancies and inflammatory
diseases.
 Cystatin C

➢ Protease inhibitor (mol wt. 13 kDa)

➢ Freely filtered at glomerulus
➢ Reabsorbed and degraded by proximal tubule
➢ Plasma concentration reflects GFR
 2. Renal tubular function tests

 Urine concentration (deprivation) Test

 Urine dilution test
 Urine acidification test
 Urine Concentration (deprivation) Test

 Fluid intake is withheld for 15 hrs.

 First urine sample in the morning is collected and
osmolality or specific gravity is measured.
 Normal: Osmolality >850 mOsmol/kg or
Sp. Gravity > 1.025
 Urine dilution test

 In dilution test, after emptying the bladder, 1 to 1.2 L of

water is given to patient.
 Then, urine specimens are collected every hour for next 4
hours.
 Normal: Osmolality< 100 mOsmol/kg or
Sp. Gravity < 1.005
 Urine acidification test/ Acid load test

 Used for the diagnosis of renal tubular acidosis

(metabolic acidosis).
 Ammonium Chloride is administered orally in gelatin
capsule (100 mg/kg body weight) to cause metabolic
acidosis.
 Then Capacity of kidney is assessed for the production of
acidic urine by collecting urine samples hourly for the
following 8 hours.
 Urinalysis

 Fresh urine sample

1. Physical examination
2. Chemical examination
3. Microscopic examination
 Physical Examination

 Appearance - Clear, turbid (Infection, nephrotic

syndrome, proteinuria)
 Colour – light yellow, Coloured ( Haematuria, jaundice)
 pH- 4.5-8
 Specific Gravity- 1.015-1.035
 Chemical Examination

 Protein
 Glucose
 Ketone bodies
 Bilirubin
 Blood
 Nitrites
 Microscopic Examination

 Cells – RBCs, WBCs, epithelial

 Casts – Granular, red cell, WBC
 Crystals- Phosphates, urates, oxalates