KIDNEY FUNCTION KIDNEY FUNCTION TESTINGTESTINGDR. MALIK ALQUB MD. PHD.

An Introduction to the Urinary System

Produces urine

Transports urine towards bladder

Temporarily store urine

Conducts urine to exterior

The Function of Urinary System

Excretion & Elimination: removal of organic wastes products

from body fluids (urea, creatinine, uric acid)

Homeostatic regulation:

Water -Salt Balance

Acid - base Balance Enocrine function:

Hormones

A(

B(

C(

excretion of excess electrolytes, nitrogenous wastes and organic acids

The maximal excretory rate is limited or established by their plasma

concentrations and the rate of their filtration through the glomeruli

The maximal amount of substance excreted in urine does not exceed the

amount transferred through the glomeruli by ultrafiltration except in the

case of those substances capable of being secreted by the tubular cells.

The excretory functionA(

B) Homeostatic Functions

Regulate blood volume and blood pressure: by adjusting volume of water lost in urine releasing renin from the juxtraglomerular apparatus

• Regulate plasma ion concentrations:

– sodium, potassium, and chloride ions (by controlling quantities lost in urine)

– calcium ion levels

Blood volume is associated with Salt volume.

The greater the blood volume the greater the blood pressure.

Removing water lowers blood pressure

1) Water -Salt Balance

The kidneys control this by excreting H+ ions and reabsorbing HCO3 (bicarbonate).

2 (Acid-Base Balance (Help stabilize blood pH)

If plasma pH is low (acidic). 

H+ secretion in the urine and HCO3¯ reabsorption back to the plasma increases  thus urine becomes more acidic,and the plasma more alkaline.

If plasma pH is high (alkaline). 

H+ secretion in the urine and HCO3¯ reabsorption back to the plasma decreases  thus urine becomes more alkaline,and the plasma more acidic.

B) Homeostatic Functions

C) The endocrine function Kidneys have primary endocrine function since they produce hormones

(erythropoietin, renin and prostaglandin).

Erythropoietin is secreted in response to a lowered oxygen content in the

blood. It acts on bone marrow, stimulating the production of red blood cells.

Renin the primary stimuli for renin release include reduction of renal

perfusion pressure and hyponatremia. Renin release is also influenced by

angiotension II and ADH.

The kidneys are primarily responsible for producing vitamin D3

In addition, the kidneys are site of degradation for hormones such as

insulin and aldosterone,

KIDNEY STRUCTURE

AND

URINE FORMATION

Each kidney consists of one million functional units: Nephrone

A) Glomerulus B) Glomerular CapsuleC) Renal Tubule proximal convoluted tubule • loop of Henle • distal convoluted tubule D)  Collecting Duct 

Nephron structure

   Blood pressure inside of the glomerulus is very high.  Because of differences in the resistance between the afferent and efferent arterioles. Forces the fluids and some solids out of the blood into the glomerular capsule.

The Glomerulus

Urine formation requiers:

Urine Formation

Glomerular Filtration Due to differences in pressure water, small molecules move from the glomerulus capillaries into the glomerular capsule

Tubular reabsorption   many molecules are reabsorbed from the nephron into the capillary (diffusion, facilitated diffusion, osmosis, and active transport)i.e.  Glucose is actively reabsorbed with transport carriers.If the carriers are overwhelmed glucose appears in the urine indicating diabetes

Tubular secretionSubstances are actively removed from blood and added to tubular fluid (active transport)ie.  H+, creatinine, and some drugs are moved by active transport from the blood into the distal convoluted tubule

a(

b(

c(

Urine Formation

Glomerular Filtration

The first step in the production of urine is called glomerular filtration.

Filtration: the forcing of fluids and dissolved substances through a membrane by pressure occurs in the renal corpuscle of the kidneys across the endothelial capsular membrane (Bowman's) capsule.

- The resulting fluid is called the filtrate.

- Filtration is a passive process.

- The total filtration rate of the kidneys is mainly determined by the difference between the blood pressure in the glomerular capillaries and the hydrostatic pressure in the lumen of the nephron

Glomerular Filtration Rate (GFR) Affected by:

1). Total filtration surface area

2). Membrane permeability

3). Net Filtration Pressure (as NFP goes up so does the GFR)

The amount of filtrate that flows out of all the renal corpuscles of both kidneys every minute

is called the glomerular filtration rate (GFR).

In the normal adult, this rate is about 120 ml/min; about 180 liters/Day

Glomerular Filtration Rate

Biochemical Tests of Renal Function

Measurement of GFR Clearance tests Plasma creatinine Urea, uric acid and β2-microglobulin

Renal tubular function tests Osmolality measurements Specific proteinurea Glycouria Aminoaciduria

Urinalysis Appearance Specific gravity and osmolality pH osmolality Glucose Protein Urinary sediments

When should you assess renal function?

Older age Family history of Chronic Kidney disease (CKD) Decreased renal mass Low birth weight Diabetes Mellitus (DM) Hypertension (HTN) Autoimmune disease Systemic infections Urinary tract infections (UTI) Nephrolithiasis Obstruction to the lower urinary tract Drug toxicity

Biochemical Tests of Renal Function

Measurement of GFR Clearance tests Plasma creatinine Urea, uric acid and β2-

microglobulin

In acute and chronic renal failure, there is effectively a loss of

function of whole nephrons

Filtration is essential to the formation of urine tests of

glomerular function are almost always required in the

investigation and management of any patient with renal disease.

The most frequently used tests are those that assess either the

GFR or the integrity of the glomerular filtration barrier.

Biochemical Tests of renal function

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, reabsorbed or metabolized by the renal

tubules.

Clearance is defined as the (hypothetical) quantity of blood or plasma completely cleared of a

substance per unit of time.

Clearance of substances that are filtered exclusively or predominantly by the glomeruli but

neither reabsorbed nor secreted by other regions of the nephron can be used to measure GFR.

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

GFR =(U V)

P

inulin

inulin

V is not urine volume, it is urine flow rate

Measurement of glomerular

filtration rate

Biochemical Tests of Renal Function

Measurement of GFR Clearance tests Plasma creatinine Urea, uric acid and β2-

microglobulin

1 to 2% of muscle creatine spontaneously converts to creatinine

daily and released into body fluids at a constant rate. Endogenous creatinine produced is proportional to muscle

mass, it is a function of total muscle mass the production

varies with age and sex Dietary fluctuations of creatinine intake cause only minor

variation in daily creatinine excretion of the same person. Creatinine released into body fluids at a constant rate and its

plasma levels maintained within narrow limits Creatinine

clearance may be measured as an indicator of GFR.

Creatinine

The most frequently used clearance test is based on the

measurement of creatinine.

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.

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,

The accurate measurement of creatinine clearance is difficult, especially in outpatients,

since it is necessary to obtain a complete and accurately timed sample of urine

Creatinine clearance clinical utility

The 'clearance' of creatinine from plasma is directly related to the

GFR if:

The urine volume is collected accurately

There are no ketones or heavy proteinuria present to interfere

with the creatinine determination.

It should be noted that the GFR decline with age (to a greater extent

in males than in females) and this must be taken into account when

interpreting results.

Creatinine clearance and clinical

utility

Use of Formulae to Predict Clearance

• Formulae have been derived to predict Creatinine Clearance (CC) from Plasma creatinine.

• Plasma creatinine derived from muscle mass which is related to body mass, age, sex.

• Cockcroft & Gault Formula CC = k[(140-Age) x weight(Kg))] / serum Creatinine (µmol/L)

k = 1.224 for males & 1.04 for females• Modifications required for children & obese subjects

• Can be modified to use Surface area

Biochemical Tests of Renal Function

Measurement of GFR Clearance tests Plasma creatinine Urea, uric acid and β2-

microglobulin

Catabolism of proteins and nucleic acids results in formation of

so called nonprotein nitrogenous compounds.

Protein

Proteolysis, principally enzymatic

Amino acids

Transamination and oxidative deamination

Ammonia

Enzymatic synthesis in the “urea cycle”

Urea

Measurement of nonprotein

nitrogen-containing compounds

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

Urea is filtered freely by the glomeruli

Plasma urea concentration is often used as an index of renal glomerular

function

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.

Plasma Urea

Many renal diseases with various glomerular, tubular, interstitial or vascular damage can

cause an increase in plasma urea concentration.

The reference interval for serum urea of healthy adults is 5-39 mg/dl. Plasma

concentrations also tend to be slightly higher in males than females. High protein diet causes

significant increases in plasma urea concentrations and urinary excretion.

Measurement of plasma creatinine provides a more accurate assessment than urea

because there are many factors that affect urea level.

Nonrenal factors can affect the urea level (normal adults is level 5-39 mg/dl) like:

Mild dehydration,

high protein diet,

increased protein catabolism, muscle wasting as in starvation,

reabsorption of blood proteins after a GIT haemorrhage,

treatment with cortisol or its synthetic analogous

Plasma Urea

Clinical Significance

States associated with 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

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

nucleosides, adenosine and guanosine.

Purines are derived from catabolism of dietary nucleic acid (nucleated cells,

like meat) and from degradation of endogenous nucleic acids.

Overproduction of uric acid may result from increased synthesis of purine

precursors.

In humans, approximately 75% of uric acid excreted is lost in the urine;

most of the reminder is secreted into the GIT

Uric acid

Renal handling of uric acid is complex and involves four sequential steps:

Glomerular filtration of virtually all the uric acid in capillary plasma

entering the glomerulus.

Reabsorption in the proximal convoluted tubule of about 98 to 100%

of filtered uric acid.

Subsequent secretion of uric acid into the lumen of the distal portion

of the proximal tubule.

Further reabsorption in the distal tubule.

Hyperuricemia is defined by serum or plasma uric acid concentrations higher

than 7.0 mg/dl (0.42mmol/L) in men or greater than 6.0 mg/dl (0.36mmol/L)

in women

Uric acid

β2-microglobulin is a small peptide (molecular weight 11.8 kDa),

It is present on the surface of most 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.

Since it is normally reabsorbed and catabolized in the tubules, measurement

of β2-microglobulin excretion provides a sensitive method of assessing

tubular integrity.

Plasma β2-microglobulin

Biochemical Tests of Renal Function

Renal tubular function tests Osmolality measurements Specific proteinurea Glycouria Aminoaciduria

Renal tubular function tests

• To ensure that important constituents such as water, sodium, glucose and a.a. are not lost from the body, tubular reabsorption must be equally efficient

• Compared with the GFR as an assessment of glomerualr function, there are no easily performed tests which measure tubular function in quantitative manner

• Investigation of tubular function:

1. Osmolality measurements in plasma and urine; normal urine: plasma osmolality ratio is usually between 1.0-3.0

2. Specific proteinuria

3. Glycosuria

4. Aminoaciduria

Proteinuria may be due to:

1. An abnormality of the glomerular basement membrane.

2. Decreased tubular reabsorption of normal amounts of filtered proteins.

3. Increased plasma concentrations of free filtered proteins.

4. Decreased reabsorption and entry of protein into the tubules consequent to tubular epithelial

cell damage.

Measurement of individual proteins such as β2-microglobulin have been used in the early

diagnosis of tubular integrity.

With severe glomerular damage, red blood cells are detectable in the urine (haematuria), the red

cells often have an abnormal morphology in glomerular disease.

Haematuria can occur as a result of lesions anywhere in the urinary tract,

Assessment of glomerular integrity

The glomerular basement membrane does not usually allow passage of

albumin and large proteins. A small amount of albumin, usually less than 25

mg/24 hours, is found in urine.

Urinary protein excretion in the normal adult should be less than 150

mg/day.

When larger amounts, in excess of 250 mg/24 hours, are detected,

significant damage to the glomerular membrane has occurred.

Quantitative urine protein measurements should always be made on

complete 24-hour urine collections.

Albumin excretion in the range 25-300 mg/24 hours is termed

microalbuminuria

Proteinuria

Normal < 150 mg/24h. TYPES OF PROTEINURIA 

Glomerular proteinuria  Tubular proteinuria  Overflow proteinuria 

Proteinuria

Glomerular proteinuria

Glomerular proteinuria — Glomerular proteinuria is due to increased filtration of macromolecules (such as albumin) across the glomerular capillary wall. The proteinuria associated with diabetic nephropathy and other glomerular diseases, as well as more benign causes such as orthostatic or exercise-induced proteinuria fall into this category. Most patients with benign causes of isolated proteinuria excrete less than 1 to 2 g/day

Tubular proteinuria

 Low molecular weight proteins — such as ß2-microglobulin, immunoglobulin light chains, retinol-binding protein, and amino acids — have a molecular weight that is generally under 25,000 in comparison to the 69,000 molecular weight of albumin. These smaller proteins can be filtered across the glomerulus and are then almost completely reabsorbed in the proximal tubule. Interference with proximal tubular reabsorption, due to a variety of tubulointerstitial diseases or even some primary glomerular diseases, can lead to increased excretion of these smaller proteins

Overflow proteinuria 

 Increased excretion of low molecular weight proteins can occur with marked overproduction of a particular protein, leading to increased glomerular filtration and excretion. This is almost always due to immunoglobulin light chains in multiple myeloma, but may also be due to lysozyme (in acute myelomonocytic leukemia), myoglobin (in rhabdomyolysis), or hemoglobin (in intravascular hemolysis

Biochemical Tests of Renal Function

Urinalysis Appearance Specific gravity and osmolality pH Glucose Protein Urinary sediments

Urinalysis is important in screening for disease is routine test for every patient, and not just

for the investigation of renal diseases

Urinalysis comprises a range of analyses that are usually performed at the point of care rather

than in a central laboratory.

Urinalysis is one of the commonest biochemical tests performed outside the laboratory.

Examination of a

patient's urine should not

be restricted to

biochemical tests.

Urinalysis

Biochemical testing of urine involves the use of commercially available disposable strips When the strip is manually immersed in the urine specimen, the reagents react with a specific component of urine in such a way that to form color

Colour change produced is proportional to the concentration of the component being tested for.

To test a urine sample:

fresh urine is collected into a clean dry container

the sample is not centrifuged

the disposable strip is briefly immersed in the urine specimen;

The colour of the test areas are compared with those provided on a colour chart

Urinalysis using disposable strips

Chemical AnalysisChemical Analysis

Urine DipstickUrine Dipstick

GlucoseGlucose

BilirubinBilirubin

KetonesKetones

Specific GravitySpecific Gravity

BloodBlood

pHpH

ProteinProtein

UrobilinogenUrobilinogen

NitriteNitrite

Leukocyte EsteraseLeukocyte Esterase

Fresh sample = Valid sample. fresh urine is collected into a clean dry container the sample is not centrifuged

Appearance: - Blood Colour (haemoglobin, myoglobin,) Turbidity (infection, nephrotic syndrome)

Urinalysis

Blue Green Pink-Orange-Red

Red-brown-black

Methylene Blue Haemoglobin Haemoglobin

Pseudomonas Myoglobin Myoglobin

Riboflavin Phenolpthalein Red blood cells

Porphyrins Homogentisic Acid

Rifampicin L -DOPA

Melanin

Methyldopa

– This is a semi-quantitative measure of concentration.

– A higher specific gravity indicates a more concentrated urine.

– Assessment of urinary specific gravity usually just confirms the impression gained by

visually inspecting the colour of the urine. When urine concentration needs to be

quantitated,

Urinalysis: Specific gravity

Urinalysis: Osmolality measurements in plasma and urine– Osmolality serves as general marker of tubular function. Because the ability

to concentrate the urine is highly affected by renal diseases.

– This is conveniently done by determining the osmolality, and then

comparing this to the plasma.

– If the urine osmolality is 600mosm/kg or more, tubular function is usually

regarded as intact

– When the urine osmolality does not differ greatly from plasma (urine:

plasma osmolality ratio=1), the renal tubules are not reabsorbing water

pH-Urine is usually acidic

-Measurement of urine pH is useful in suspected drug toxicity, abuse.., or where there is an unexplained metabolic acidosis (low serum bicarbonate or other causes…).

Urine sediments-Microscopic examination of sediment from freshly passed urine involves looking for

cells, casts, fat droplets

-Blood: haematuria is consistent with various possibilities ranging from malignancy through urinary tract infection to contamination from menstruation.

-Red Cell casts could indicate glomerular disease

-Crystals

-Leucocytes in the urine suggests acute inflammation and the presence of a urinary tract infection.

Urinalysis

-are cylindrical structures produced by the kidney and present in the urine in

certain disease states. - They form in the distal convoluted tubule and collecting ducts of nephrons,

then dislodge and pass into the urine, where they can be detected by

microscope.- They form via precipitation of Tamm-Hrsfall mucoprotein which is

secreted by renal tubule cells, and sometimes also by albumin.

Urinary casts

Red blood cell cast in urineWhite blood cell cast in urine

Urinary casts. (A) Hyaline cast (200 X); (B) erythrocyte cast (100 X); (C) leukocyte cast (100 X); (D) granular cast (100 X)

Urinary crystals. (A) Calcium oxalate crystals; (B) uric acid crystals (C) triple phosphate crystals with amorphous phosphates ; (D) cystine crystals.

• Crystals

- Water homeostasis is determined by several interrelated processes:

1. Water intake and water formed through oxidation of food stuffs.

2. Extra-renal water loss: insensible water loss the via faeces, and sweating.

3. A solute load to be excreted that is derived from ingested minerals and

nitrogenous substances.

4. The ability of the kidneys to produce concentrated or dilute urine.

5. Other factors such as vomiting and diarrhoea become important in various

disease states;

loss of ability to produce concentrated urine is a feature of virtually all types

of chronic renal diseases.

Urine volume

To maintain water homeostasis, the kidneys must produce urine in a volume

precisely balances water intake and production to equal water loss through extra

renal routes.

Minimum urine volume is determined by the solute load to be excreted whereas

maximum urine volume is determined by the amount of excess water that must be

excreted

Urine volume

Causes of polyurea

Increased osmotic load, e.g due to glucose

Increased water ingestion

Diabetes insipidus: - Failure of ADH production results

in marked polyuria (diabetes insipidus), which stimulates

thirst and greatly increases water intake

Nephrogenic diabetes insipidus: The kidneys’ lack of

response to ADH has similar effect ( failure of the

tubules to respond to Vassopressin (ADH

MAJOR CAUSES OF KIDNEY DISEASE   The causes of acute or chronic kidney disease are

traditionally classified by that portion of the renal anatomy most affected by the disorder. Renal function is based upon four sequential steps, which are isolated to specific areas of the kidney or surrounding structures: First, blood from the renal arteries and their

subdivisions is delivered to the glomeruli. The glomeruli form an ultrafiltrate, nearly free of

protein and blood elements, which subsequently flows into the renal tubules.

The tubules reabsorb and secrete solute and/or water from the ultrafiltrate.

The final tubular fluid, the urine, leaves the kidney, draining sequentially into the renal pelvis, ureter, and bladder, from which it is excreted through the urethra.

Prerenal disease

 The two major causes of reduced renal perfusion are volume depletion and/or relative hypotension. This may result from true hypoperfusion due to bleeding, gastrointestinal, urinary, or cutaneous losses, or to effective volume depletion in heart failure, shock, or cirrhosis.

Prerenal disease is most commonly associated with an acute time course. However, among patients with chronic kidney disease, the addition of a prerenal process may result in acute renal dysfunction

Glomerular disease 

 There are numerous idiopathic and secondary (due to neoplasia, autoimmunity, drugs, genetic abnormalities, and infections) disorders that produce glomerular disease. Two general patterns (with considerable overlap in some diseases) are seen: A nephritic pattern, which is associated with

inflammation on histologic examination and produces an active urine sediment with red cells, white cells, granular and often red cell and other cellular casts, and a variable degree of proteinuria.

A nephrotic pattern, which is not associated with inflammation on histologic examination and is associated with proteinuria, often in the nephrotic range, and an inactive urine sediment with few cells or casts.

Tubular and interstitial disease   As with vascular disease, the tubular and

interstitial diseases affecting the kidney can be divided into those that produce acute and chronic disease: Hereditary, systemic, toxic, and drug-induced causes predominate. The most common acute tubulointerstitial

disorders are acute tubular necrosis, which typically occurs in hospitalized patients.

The major chronic tubulointerstitial disorders are polycystic kidney disease

Obstructive uropathy

Obstruction to the flow of urine can occur anywhere from the renal pelvis to the urethra. The development of renal insufficiency in patients without intrinsic renal disease requires bilateral obstruction (or unilateral obstruction with a single functioning kidney) and is most commonly due to prostatic disease (hyperplasia or cancer) or metastatic cancer. The time course can be acute or chronic

Nephrotic syndrome

 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: Nephrotic range proteinuria — Urinary protein

excretion greater than 50 mg/kg per day Hypoalbuminemia — Serum albumin

concentration less than 3 g/dL (30 g/L) Edema Hyperlipidemia