Kidney Function Tests. Main Functions of the Kidney. 1- Excretion of metabolic waste products & foreign chemicals 2- Regulation of water & électrolyte balance 3- Regulation of acid - base balance 4- Regulation of arterial blood pressure
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1- Excretion of metabolic waste products & foreign chemicals
2- Regulation of water & électrolyte balance
3- Regulation of acid - base balance
4- Regulation of arterial blood pressure
5- Production of erythropoietin & activation of vitamin D
6- Other metabolic functions (as gluconeogenesis, etc..)
1- Pre-renal diseases
2- Glomerular diseases
3- Tubular & interstitial diseases
4- Obstructive uropathies
Volume depletion (reduced volume of blood to the glomeruli)
and/or relative hypotension
Associated with inflammation on histological examination
Active urine sediment with RBCs, WBCs, granular, red cell & other cellular casts
Variable degree of proteinuria (mild to moderate in most cases).
Not associated with inflammation on histological examination
Proteinuria (moderate to severe . Most cases heavy proteinuria)
An inactive urine sediment with few RBCs &WBCs cells or casts.
The tubular and interstitial diseases affecting the kidney can be divided into
those that produce acute and chronic disease:
Obstruction to the flow of urine can occur anywhere from the renal pelvis to
The nephrotic syndrome is caused by renal diseases that increase the permeability across the
glomerular filtration barrier.
It is classically characterized by four clinical features, but the first two are used diagnostically
because the last two may not be seen in all patients.
1- Proteinuria: Urinary protein excretion greater than 50 mg/kg per day (heavy proteinuria)
2- Hypoalbuminaemia: Serum albumin concentration less than 3 g/dL (30 g/L)
4- Hyperlipidemia: increased cholesterol in blood
Nephrotic syndrome is diagnosed by:
Plasma Proteins Electrophoresis
1- Assessment of Glomerular Functions
2- Assessment of Tubular Functions
Assessment of glomerular filtration rate (GFR) is
used an index of glomerular functions
Measurement of GFR
Is The first step in the production of urine
Glomerular Filtration Rate (GFR)
The amount of filtrate that flows out of all the renal
corpuscles of both kidneys every minute
In the normal adult, this rate is about 120 ml/minute
i.e. about 180 liters / day
GFR provides a useful index of the number of functioning glomeruli
GFR can be estimated
by measuring the urinary excretion of a substance that is completely filtered from the blood by the glomeruli and it is not secreted, not reabsorbed & not metabolized by the renal tubules.
U X V
Clearance (ml/min) = __________________________________
Measurement of glomerular Filtration Rate
U is the concentration of substance in urine (in mmol/L)
V is urine flow rate (in ml/min)
P is the concentration of substance in bloodinmmol/L)
Inulin clearance test
Measurement of inulin clearance requires the infusion of inulin into the blood and is not suitable for routine clinical use
Advantage of inulin clearance test over creatinine clearance test:
Small quantity of creatinine is reabsorbed by the tubules and other quantities are actively secreted by the renal tubules So creatinine clearance is approximately 7% greater than inulin clearance.
The difference is not significant when GFR is normal but when the GFR is low (less 10 ml/min), tubular secretion makes the major contribution to creatinine excretion and the creatinine clearance significantly overestimates the GFR (gives values greater than real ).
Blood Urea X V
Blood Uric Acid X V
Blood Uric Acid X Vcont.
Plasma X Vβ2-microglobulin
1- A small protein
2- Present on the surface of most cells and in low concentrations in the plasma.
3- Completely filtered by the glomeruli & is reabsorbed & catabolized by proximal tubular cells.
Results of measuring blood levels of β2-microglobulin:
1- Is a good index of GFR in normal people (as it is not affected by diet or muscle mass)
2- Since it is normally reabsorbed and catabolized in the tubules, β2-microglobulin blood level
provides a sensitive method of assessing tubular functions.
It is increased in certain malignancies and inflammatory diseases.
Renal tubular functions is assessed by:
Osmolality: weight of solutes/ weight of solvent
Urine osmolality: Concentration of all solutes (weight of all solutes / weight of urine)
So, urine osmolality serves as general marker of tubular function.
Results of urine osmolality
A patient with polyuria due to chronic renal failure is unable to produce
either a dilute or concentrated urine
Instead urine osmolality is generally within 50 mmol/kg of the plasma
Proteinuria X V
Normal protein amount n urine is < 200 mg/24hours urine collection
Quantitative urine protein measurements should always be made on complete
24-hour urine collections.
Types of proteinuria
1- Diabetic nephropathy
2- Nephrotic syndrome
Low molecular weight molecules such as smaller proteins (ß2-microglobulin, immunoglobulin light chains, retinol-binding protein ) & amino acids have molecular weights that are generally less than 25,000 in comparison to the 69,000 molecular weight of albumin.
Smaller molecules (including smaller proteins & amino acids) can be filtered across the glomeruli & are then almost completely reabsorbed in the proximal tubule.
Interference with proximal tubular reabsorption can lead to increased excretion of these smaller proteins & amino acids (aminoaciduria)
N.B. aminoaciduria due to inborn errors of amino acids metabolism must be excluded to diagnose tubular defects.
1- Immunoglobulin light chains in multiple myeloma
2- lysozymesin acute myelomonocyticleukemia & in rhabdomyolysis
3- Hemoglobin in intravascular hemolysis