Renal Function Tests Flashcards
What are the functions of the urinary system?
(3)
Excretion and elimination
Homeostatic regulation
Endocrine function
What does the urinary system excrete?
(3)
Urea
Creatinine
Uric acid
What does the urinary system have homeostatic control over?
(2)
Water-Salt balance
Acid-base balance
What hormones does the urinary system have control over?
(3)
EPO
Renin
1-25 VitD
What does acidic urine mean
High amount of H+ ions in the urine -> body trying to get rid of these H+ ions
What are the three basic renal processes
Glomerular filtration
Tubular reabsorption
Tubular secretion
What happens if glomerular filtration rate is low?
This means waste products will build up in blood and there will be less of these products in urine
This means the glomeruli filter less blood
How high is glomerular filtration usually?
180L/day
Why is glomerular filtration rate so high?
Lots of opportunity to precisely regulate extracellular fluid composition and get rid of unwanted substances (ECF is being regulated not the urine)
Explain in your own words how renal filtration works?
Renal system filters ECF and blood -> waste forms urine and is excreted
How much urine is excreted daily?
1.5L
What is the relationship between urine and cardiac output
Urine excretion = 20% of cardiac output
What is plasma renal flow?
600ml/Minute
What is GFR also called
Ultrafiltration
How much is reabsorbed after glomerular filtration
99%
What is urine in terms of filtration?
The ultrafiltration of blood
What percentage of urea is reabsorbed and why?
Only 50.6% is reabsorbed as it is a very small molecule
What percentage of creatinine is reabsorbed?
0% is reabsorbed it is all excreted in urine
What gets filtered/passes through the glomeruli
(7)
H2O
Electrolytes
Glucose
Urea
Creatinine
Insulin
Small molecular weight proteins
What is not filtered/will not pass through the glomeruli?
(2)
Large molecular weight proteins
Blood cells
What drives the reabsorption of glucose and amino acids?
Active transport carriers
How does the renal system control secretion
Secretion of waste products involves transport across capillary membranes and kidney tubules
The kidney has an excretion role, what does this do?
Excretion is needed for the maintenance of blood volume, pH, ion concentrations
What are the two types of substances removed by the renal system?
By-products of metabolism
Foreign substances, e.g. drugs/environmental toxins
What by-products of metabolism are removed by the renal system
(3)
Creatinine from muscle metabolism
Urea from protein metabolism
Urate from purine metabolism
What foreign substances are removed by the renal system?
(2)
Saccharin in artificial sweetener
Benzoate in diet soda
How does the kidney regulate blood plasma?
The kidney regulates blood plasma (and interstitial fluid) volume (and therefore blood pressure)
What is the glomerular filtration rate (GFR)?
The volume of filtrate produced by both kidneys each minute
Approx 120 mls/min or 180L/day
How would you know something was wrong with the renal system?
No urine
No EPO
What would no EPO production mean?
Anaemia will result
What are the three types of renal problems?
Pre-renal
Renal
Post-renal
What are some examples of pre-renal causes of kidney failure?
(2)
Decreased extracellular fluid volume
Myocardial ischemia
What is a cause of renal caused kidney failure?
Acute tubular necrosis
What are the causes of postrenal kidney failure?
Ureteral obstruction (stones)
What does it mean if there is a pre-renal cause of kidney failure?
This means the kidney is healthy
There is a problem with circulation etc
What does it mean if there is a post-renal cause of kidney failure?
This means the kidney is healthy
There is a problem with the ureters, urethra
What are the signs and symptoms of renal failure?
(6)
Azotaemia (increase in blood urine nitrogen)
Disorders of micturation
Disorders of urine volume
Alterations in urine composition
Pain
Oedema
What is azotaemia?
Increase in blood urine nitrogen
What does azotaemia cause?
Uraemia
What is uraemia?
Build up of toxic chemicals due to the kidneys becoming damaged - build up of urea
What are the symptoms of uraemia
(3)
Nausea
Vomiting
Lethargy
What are the symptoms of disorders of micturation?
(4)
Increased frequency
Nocturia
Retention
Dysuria
What are the three disorders of urine volume?
Polyuria
Oliguria
Anuriai
What are some examples of alterations in urine composition
(5)
Haematuria
Proteinuria
Bacteriua
Leujocyturia
Calculi
What causes oedema (due to renal failure)?
(2)
Hypoalbuminemia
Salt and water retention
Why might renal failure cause pain?
Due to the presence of stones
What are renal function tests used for?
(3)
To detect renal damage
To monitor functional damage
To distinguish between impairment and failure
Why is urine light yellow?
Urobilin (urochrome) which is a Hb breakdown product
Describe how bilirubin becomes urobilin
(4)
Bile is converted to urobilinogen in the gut by microbes
Some of this urobilinogen remains in the large intestine and is converted to stercobilin which gives faeces its brown colour
Some of the urobilinogen is reabsorbed into the bloodstream and then delivered to kidney
When urobilinogen is exposed to air, it is oxidised to urobilin, giving urine its yellow colour
What is analysed in urinalysis?
Appearance
Specific gravity and osmolarity
pH
Glucose
Protein
Urinary sediments?
How is GFR measured?
Clearance tests
Plasma creatinine
What are the three types of renal tests
Urinalysis
Measurements of GFR
Tubular Functions Tests
What are urinalysis dipsticks
(2)
Sticks which usually have up to 10 test areas
They measure semi-quantatively urinary nitrites, pH, protein, glucose, ketones, urobilinogen, bilirubin, leukocytes and blood (haemoglobin)
What lab tests can be carried out to test renal function?
GFR
Creatinine clearance
Plasma creatinine
Plasma urea
Plasma sodium
Plasma potassium
Urine volume
Urine urea
Urine sodium
Urine protein
Urine glucose
Haematuria
What is oliguria?
Low urine output
What is anuria?
Lack of urine
What is polyuria?
Frequent uria
How are nitrogenous wastes produced?
Produced from the catabolism of amino acids and nucleic acids
How are nitrogenous wastes eliminated from the body?
(2)
First is the removal of the amino (-NH2) group and its combination with H= to form ammonia (NH3) in the liver
Ammonia is toxic so it is converted to urea in the liver
What is urea called in US?
Blood urea nitrogen
How is urea excreted?
(3)
Filtered at glomerulus
40% is reabsorbed
More is reabsorbed if the rate of tubular flow is slow (due to renal hypoperfusion)
What might increase plasma urea?
(7)
GI bleed
Trauma
Renal hypoperfusion
Decreased ECFV
Acute renal impairment
Chronic renal disease
Post-renal obstruction (calculus tumour)
What is plasma creatinine?
(3)
Waste product of muscle metabolism
Increases in concentration as GFR decreases
Not proportional to renal damage
When is urea excretion high
When dehydrated
What renal test results indicates dehydration?
Normal creatinine but high urea
Is creatinine proportional to renal health?
No its not proportional to renal damage
What is important about plasma creatinine levels?
The change in values within an individual patient is usually more important than the absolute value
What happens to plasma creatinine in chronic renal disease?
(2)
It may increase to 1000 umol/L
The plot of plasma creatinine concentration vs time can predict when intervention is required in end stage renal failure
What is normal creatinine levels proportional to?
(2)
Normal creatinine is proportional to muscle mass
Men have a higher RR than females, muscly men have a higher range than females
What does it mean if plasma creatinine value doubles
This means GFR and renal function has probably fallen to half of normal
What is uric acid also called
Urate
What is uric acid/urate
(2)
The end product of purine metabolism
The kidneys excrete two-thirds of uric acid produced daily, remaining one third is excreted in stool
Where do we get purines from?
(2)
Dietary sources such as organs (liver, kidney), sweetbreads, sardines, anchovies, lentils, muschrooms, spinach and asparagus
Get it from the breakdown of body proteins
What happens if uric acids build up?
(3)
High levels of uric acid in the blood forms urate crystals
Gout occurs when urate crystals accumulate in your joint
This causes inflammation and intense pain of a gout attack
What is the principle behind GFR measurement
Measurement is based on the concept of clearance
The determination of the volume of plasma from which a substance is removed by glomerular filtration during it’s passage through the kidney
What is renal clearance?
The ability of the kidneys to remove molecules from plasma and excrete those molecules in the urine
Renal clearance = (filtration + secretion) - reabsorption
Write a note on GFR
(5)
The volume of fluid filtered into Bowman’s space per unit time
Its the best overall index of kidney function
It can be regulated
Gold standard techniques not practical for the entire chronic kidney disease population.
More practical than creatinine clearance, more sensitive
What is used to estimate GFR
Urinary clearance of filtration markers
What are two characteristics of ideal filtration markers?
Freely filtered
Neither secreted nor absorbed by kidney tubule
What is the gold standard exogenous substance used to estimate GFR
Inulin (found in garlic)
IV infusion
But difficult to assay
Give two substances other than inulin used to estimate GFR
Cr51 - EDTA
I^125 - iothalamate
Write a note on how creatinine clearance is used as a marker of GFR
(5)
The subject collected all the urine produced over 24 hours into a container
A portion of urine is used to measure the creatinine concentration, Ucreat (= Urinary creatinine)
A blood sample during the same 24 hours is required for the measurement of Pcreat (=Plasma creatinine)
Many subjects find it difficult to make a complete urine collection over this length of time. Urine goes into the toilet rather than in to the container
Variation of up to 20% has been shown
Why is creatinine clearance so hard for subjects to measure?
Many subjects find it difficult to make a complete urine collection over this length of time. Urine goes into the toilet rather than in to the container
Variation of up to 20% has been shown
What are the units for creatinine clearance
Mls/min
What is Ucreat
Urine creatinine concentration (umol/L)
What is Pcreat
Plasma creatinine concentration (umol/L)
How does a healthy person’s creatinine clearance compare to their GFR
In healthy it is 10-30% higher than GFR
What might increase the tubular secretion of creatinine
Chronic renal disease
What might inhibit the tubular secretion of creatinine
Drugs e.g. salicylate, cimetidine
Overall why is creatinine clearance an unreliable test
Problems with collection
Drugs or chronic renal disease can affect GFR
What are the four main tests carried out for renal function and comment on if they are practical or not?
Glomerular filtration rate = impractical
Creatinine clearance = unreliable
Plasma creatinine = specific but insensitive
Plasma urea = subject to problems
What is eGFR and how is it worked out
(3)
Estimated Glomerular Filtration Rate
Equations based on serum creatinine but taking into account non-renal influences improve its relationship with GFR
Equation includes serum creatinine, age, gender, race and body size
Give an example of an eGFR equation
Modification of Diet in Renal Disease Study = MDRD equation
CKD-EPI Equation -> Chronic Kidney Disease Epidemiology Collaboration
Compare the CKD-EPI and GFR equations
The CKD_EPI equation was shown to perform better than the MDRD equation espiecially at higher GFR, with less bias and greater accuracy
Define renal failure
A deterioration in renal function leading to a complex of symptoms and signs
What are the two signs of renal failure
Azotaemia
Uraemia
What is azotaemia
Increase in nitrogenous substances e.g. urea and creatinine
What is uraemia
Symptoms of confusion etc associated with azotaemia
What are the two types of kidney disease
Acute Kidney Injury
Chronic Kidney Disease
What is the difference between acute kidney injury and chronic kidney disease
AKI = quick onset, occurs over hours/days
CKD = progressive loss in kidney function over a period of months or years
What was acute kidney injury previously called
Acute renal failure (ARF)
How is acute kidney injury defined?
As an abrupt decline in renal function, clinically manifesting as a reversible acute increase in nitrogen waste products - measured by serum urea and serum creatinine levels or inability of the kidneys to produce sufficient amounts of urine - over the course of hours to weeks
What generally causes acute kidney injury
(4)
Generally it occurs because of damage to the kidney caused by decreased renal blood flow (renal ischemia) from any cause (e.g. low blood pressure)
Exposure to substances harmful to the kidney
An inflammatory process in the kidney
An obstruction of the urinary tract which impedes the flow of urine
What may acute kidney injury lead to?
(5)
Metabolic acidosis
High potassium levels
Uraemia
Changes in body fluid balance
Effects on other organs systems, including death
What risk is increased later in life by having suffered from AKI
Risk of chronic kidney disease is greatly increased
How is AKI managed
Treatment of the underlying cause and supportive care, such as renal replacement therapy
How many stages to chronic kidney disease are there?
Five stages
How is chronic kidney disease classified?
Based on measured or estimated GFR
What GFR indicates stage 1 CKD
GFR of more than 90
What GFR indicates stage 5 CKD
GFR less than 15
What is stage 1 CKD
Kidney damage (protein in urine) and normal GFR
What is stage 2 CKD
Kidney damage and mild decrease in GFR
What is stage 3 CKD
Moderate decrease in GFR
What is stage 4 CKD
Severe decrease in GFR
What is stage 5 CKD
Kidney failure - End stage renal disease (dialysis or kidney transplant needed)
What are the signs and symptoms of renla failure
(6)
Symptoms of uraemia caused by azotaemia
Disorders of micturation (frequency, nocturia, retention, dysuria)
Disorders of urine volume (poyluria, oliguria, anuria)
Alterations in urine composition (haematuria, proteinuria, bacteriua, leucjoxyturia, calculi)
Pain
Oedema
What happens when extracellular fluid volume falls
Blood pressure falls
What happens when blood volume and pressure is really low
Not adequate flow to brain and other organs
Why do the kidneys work with the cardiovascular system?
To maintain pressure in acceptable range
What causes the production of renin
(3)
Low blood pressure
Low blood volume
Low sodium
What is angiotensinogen converted into and by what?
Angiotensinogen is converted into angiotensin I by renin
What is angiotensin I converted into and by what
Angiotensin I is converted into Angiotensin II by angiotensin converting factor
What blocks angiotensin converting enzyme
ACE-I
What are ACE-Is?
Ace Inhibitors
A group of medicines that are mainly used to treat certain heart and kidney conditions; however, they may be used in the management of other conditions such as migraine and scleroderm
What does angiotensin II act on
Systemic vasoconstriction
Renal vasoconstriction
What affects does angiotensin II have on the kidney
(2)
Affects renal vasoconstriction which decreases blood flow which decreases glomerular filtration
This causes the retention of sodium and water and increases loss of potassium ion
All of these increase blood pressure
What affects does aldosterone have?
(3)
Increases sodium/potassium exchange
This results in increased retention of sodium and H2O but the increased loss of potassium ions
This increases blood pressure
How is total blood volume measured
300 milliosmoles/L
What are milliosmole?
Measure of osmolarity: the total number of dissolved particles (glucose, protein, etc) per liter of solution
What is sodium
(4)
Na
Major extracellular cation
10 mmol/L intracellularly
140 mmol/L extracellularly (blood)
How much sodium should we intake a day?
100-200 mmol/day
How much sodium is excreted in the faeces, sweat, renal?
10 mmol/day in faeces
10-20 mmol/day in sweat
The rest matches intake
Describe the relationship between sodium and water
Where sodium goes, water follows
Write about the regulation of water
(2)
Thirst regulates input
Anti-diuretic hormone (vasopressin) regulates water output
Write a note about the regulation of sofium
Renin-angiotensin-aldosterone (RAA)
Natriuretic peptides
Both regulate output
What is antidiuretic hormone ADH also called?
Vasopressin
What is Antidiuretic hormone?
(4)
Hormone from posterior pituitary
Released in response to high osmolarity
Released in response to low volume -> low volume over-rides low osmolality
Increases permeability of kidney distal tubule
What does ADH control
Renal water excretion
Its also a potent vasoconstrictor
What does low ADH mean?
High urine volume
Low urine osmolality
What does high ADH mean?
Low urine volume
High urine osmolality
Give one cause of increased osmolality
Hypernatraemia
What may cause hypernatraemia
Dehydration
What is RAA
Renin-angiotension-aldosteron
What causes release of renin
Low renal perfusion
What causes low renal perfusion?
Hypovolaemia
Heart failure
Shock
What does Angioitensin II do>
Releases aldosterone from adrenal gland
What does aldosterone do?
Acts in the proximal tubule
Reabsorbs sodium and excretes potassium
i.e. it controls urine sodium excretion
What would ACE inhibitors be used to treat?
Hypertension
What do diuretics do?
(5)
Excrete more urine
Lower blood volume
Lower blood pressure
Excessive potassium loss (important for muscles)
Many different kinds
How do the kidneys help maintain normal blood pH
(2)
Kidneys help with response to alkalosis or acidosis
They excrete H+, reabsorb bicarbonate indirectly through carbonic anhydrase
What buffers are found in blood
NH3 (ammonia)
PO4^-3
Explain in your own words how the kidneys keep the blood at the correct pH
(3)
If extracellular fluid becomes acidic, kidneys remove H+ and conserve bicarbonate (HCO3)
HCO3- acts as buffer
If fluid becomes too alkalinic, kidneys remove HCO3 and conserve H+
How does the body maintain ion balance
Key ions kept normal via balance of dietary intake and urine loss
Sodium, Potassium and Calcium well regulated
What are electrolytes
Substances that become ions in solution and acquire the capacity to conduct electricity
Why is electrolyte balance important?
Its essential for normal function of our cells and our organs (intracellular and extracellular)
Maintenance of osmotic gradients is important as these affect and regulate the hydration of the body, blood pH and are critical for nerve and muscle function
What are electrolytes related to in the body?
(4)
Fluid balance
pH
Membrane potential
Tissue excitability
List the six important electrolytes
Sodium
Potassium
Chloride
Bicarbonate
Calcium
Phosphate (these two are for bone, muscle contraction etc)
Write a note on sodium
(3)
Major role in regulating the amount of water in the body
The passage of sodium in and out of cells is necessary for many body functions like transmitting electrical signals in the brain and in the muscle
The sodium levels are measured to detect whether there’s the right balance of sodium and liquid in the blood to carry out those functions
Write a note on potassium
(3)
Its essential to regulate how the heart beats
When potassium levels are too high or too low, it can increase the risk of an abnormal heartbeat
Low potassium levels are also associated with muscle weakness
Write a note on chloride
(2)
It helps maintain a balance of fluids in the body
If there’s a large loss of chloride, the blood may become more acidic and prevent certain chemical reactions from occurring in the body that are necessary for it to keep working properly
Write a note on bicarbonate
(3)
Prevents the body’s tissues from getting too much or too little acid
The kidney and lungs balance the levels of bicarbonate in the body
So if bicarbonate levels are too high or low, it might indicate that there’s a problem with those organs
Describe the reabsorption of sodium
(4)
60-70% is reabsorbed together with bicarbonate and water
25-30% is reabsorbed in the ascending loop of Henle
Only a small fraction of the original filter load is presented to the distal tubule
The distal tubule absorbs sodium under the influence of aldosterone, here the sodium is coupled to the exchange of potassium and/or hydrogen ions that ultimately determine the amount of sodium excreted in the urine
How is sodium absorbed by the distal tubule
Only a small fraction of the original filter load is presented to the distal tubule
The distal tubule absorbs sodium under the influence of aldosterone, here the sodium is coupled to the exchange of potassium and/or hydrogen ions that ultimately determine the amount of sodium excreted in the urine
What causes hypernatremia
Excess water loss (severe vomiting, diarrhea, or polyuric state)
Increased renal sodium conservation
What causes hyponatremia
Decreased tubular reabsorption as a result of inappropriate diuretic therapy, primary or secondary hypoaldosteronism
Describe the absorption of potassium
(3)
Potassium is filtered at the glomerulus
Approximately 90% is reabsorbed in the proximal tubule and the ascending loop of Henle
10% reaches the distal tubule where the regulation of body potassium occurs through secretion in exchange for sodium under the influence of aldosterone
What may cause hyperkalaemia
Due to transcellular shift intake in intake, and or decrease in output
What may cause hypokalaemia
Increased loss, transcellular shift, or decreased intake of potassium
What are some complications of untreated hypokalaemia or hyperkalaemia?
High morbidity and mortality
What is the chemical formula for the bicarbonate ion
HCO3-
Write a note on the bicarbonate ion
(3)
Its the chemical species that comprises almost all the CO2 produced by the body
They are completely filtered by the glomeruli with approximately 90% reabsorption in the proximal tubule and a further 10% in the distal tubule
The threshold for this system is approximately 26 mmol/L; at concentrations above this level bicarbonate is excreted in the urine
What increases bicarbonate concentration of serum?
(2)
Increases in metabolic alkalosis
In compensated respiratory acidosis
What decreases serum bicarbonate?
(2)
Metabolic acidosis
Compensated respiratory alkalosis
Write a note on chloride (Cl-)
(3)
The major anion involved in extracellular fluid balance and makes up about two-thirds of the inorganic anion in plasma
Chloride is measured routinely along with other electrolytes, sodium, potassium and carbon dioxide and results are used to calculate the anion gap
When chloride is selectively depleted most common seen in vomiting, nasogastric suction, the patient developed a metabolic alkalosis. the anion gap is much increased
What happens in renal insuffiency?
(4)
Happens in kidney disease
Nephrons are destroyed/reduced renal function
Clinical manifestations include salt and water retention, uraemia, high plasma urea, elevated plasma (H+) acidosis, and K+ which is dangerous to the heart
Dialysis is needed
What is dialysis
(2)
A machine used for the treatment of renal insufficiency
Molecules diffuses through selectively permeable membrane
What is haemodialysis
This removes solutes (waste particles) and fluid from the blood across a semipermeable membrane in a filter (dialyzer)
