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2.2 Clinical Chemistry > Renal Function Tests > Flashcards

Renal Function Tests Flashcards

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1
Q

What are the functions of the urinary system?
(3)

A

Excretion and elimination

Homeostatic regulation

Endocrine function

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2
Q

What does the urinary system excrete?
(3)

A

Urea
Creatinine
Uric acid

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3
Q

What does the urinary system have homeostatic control over?
(2)

A

Water-Salt balance
Acid-base balance

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4
Q

What hormones does the urinary system have control over?
(3)

A

EPO
Renin
1-25 VitD

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5
Q

What does acidic urine mean

A

High amount of H+ ions in the urine -> body trying to get rid of these H+ ions

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6
Q

What are the three basic renal processes

A

Glomerular filtration
Tubular reabsorption
Tubular secretion

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7
Q

What happens if glomerular filtration rate is low?

A

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

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8
Q

How high is glomerular filtration usually?

A

180L/day

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9
Q

Why is glomerular filtration rate so high?

A

Lots of opportunity to precisely regulate extracellular fluid composition and get rid of unwanted substances (ECF is being regulated not the urine)

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10
Q

Explain in your own words how renal filtration works?

A

Renal system filters ECF and blood -> waste forms urine and is excreted

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11
Q

How much urine is excreted daily?

A

1.5L

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12
Q

What is the relationship between urine and cardiac output

A

Urine excretion = 20% of cardiac output

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13
Q

What is plasma renal flow?

A

600ml/Minute

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14
Q

What is GFR also called

A

Ultrafiltration

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15
Q

How much is reabsorbed after glomerular filtration

A

99%

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16
Q

What is urine in terms of filtration?

A

The ultrafiltration of blood

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17
Q

What percentage of urea is reabsorbed and why?

A

Only 50.6% is reabsorbed as it is a very small molecule

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18
Q

What percentage of creatinine is reabsorbed?

A

0% is reabsorbed it is all excreted in urine

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19
Q

What gets filtered/passes through the glomeruli
(7)

A

H2O
Electrolytes
Glucose
Urea
Creatinine
Insulin
Small molecular weight proteins

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20
Q

What is not filtered/will not pass through the glomeruli?
(2)

A

Large molecular weight proteins

Blood cells

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21
Q

What drives the reabsorption of glucose and amino acids?

A

Active transport carriers

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22
Q

How does the renal system control secretion

A

Secretion of waste products involves transport across capillary membranes and kidney tubules

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23
Q

The kidney has an excretion role, what does this do?

A

Excretion is needed for the maintenance of blood volume, pH, ion concentrations

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24
Q

What are the two types of substances removed by the renal system?

A

By-products of metabolism

Foreign substances, e.g. drugs/environmental toxins

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25
Q

What by-products of metabolism are removed by the renal system
(3)

A

Creatinine from muscle metabolism
Urea from protein metabolism
Urate from purine metabolism

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26
Q

What foreign substances are removed by the renal system?
(2)

A

Saccharin in artificial sweetener
Benzoate in diet soda

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27
Q

How does the kidney regulate blood plasma?

A

The kidney regulates blood plasma (and interstitial fluid) volume (and therefore blood pressure)

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28
Q

What is the glomerular filtration rate (GFR)?

A

The volume of filtrate produced by both kidneys each minute

Approx 120 mls/min or 180L/day

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29
Q

How would you know something was wrong with the renal system?

A

No urine
No EPO

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30
Q

What would no EPO production mean?

A

Anaemia will result

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31
Q

What are the three types of renal problems?

A

Pre-renal

Renal

Post-renal

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32
Q

What are some examples of pre-renal causes of kidney failure?
(2)

A

Decreased extracellular fluid volume

Myocardial ischemia

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33
Q

What is a cause of renal caused kidney failure?

A

Acute tubular necrosis

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34
Q

What are the causes of postrenal kidney failure?

A

Ureteral obstruction (stones)

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35
Q

What does it mean if there is a pre-renal cause of kidney failure?

A

This means the kidney is healthy
There is a problem with circulation etc

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36
Q

What does it mean if there is a post-renal cause of kidney failure?

A

This means the kidney is healthy
There is a problem with the ureters, urethra

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37
Q

What are the signs and symptoms of renal failure?
(6)

A

Azotaemia (increase in blood urine nitrogen)

Disorders of micturation

Disorders of urine volume

Alterations in urine composition

Pain

Oedema

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38
Q

What is azotaemia?

A

Increase in blood urine nitrogen

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39
Q

What does azotaemia cause?

A

Uraemia

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40
Q

What is uraemia?

A

Build up of toxic chemicals due to the kidneys becoming damaged - build up of urea

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41
Q

What are the symptoms of uraemia
(3)

A

Nausea
Vomiting
Lethargy

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42
Q

What are the symptoms of disorders of micturation?
(4)

A

Increased frequency
Nocturia
Retention
Dysuria

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43
Q

What are the three disorders of urine volume?

A

Polyuria
Oliguria
Anuriai

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44
Q

What are some examples of alterations in urine composition
(5)

A

Haematuria
Proteinuria
Bacteriua
Leujocyturia
Calculi

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45
Q

What causes oedema (due to renal failure)?
(2)

A

Hypoalbuminemia
Salt and water retention

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46
Q

Why might renal failure cause pain?

A

Due to the presence of stones

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47
Q

What are renal function tests used for?
(3)

A

To detect renal damage

To monitor functional damage

To distinguish between impairment and failure

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48
Q

Why is urine light yellow?

A

Urobilin (urochrome) which is a Hb breakdown product

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49
Q

Describe how bilirubin becomes urobilin
(4)

A

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

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50
Q

What is analysed in urinalysis?

A

Appearance
Specific gravity and osmolarity
pH
Glucose
Protein
Urinary sediments?

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51
Q

How is GFR measured?

A

Clearance tests
Plasma creatinine

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52
Q

What are the three types of renal tests

A

Urinalysis
Measurements of GFR
Tubular Functions Tests

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53
Q

What are urinalysis dipsticks
(2)

A

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)

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54
Q

What lab tests can be carried out to test renal function?

A

GFR
Creatinine clearance
Plasma creatinine
Plasma urea
Plasma sodium
Plasma potassium
Urine volume
Urine urea
Urine sodium
Urine protein
Urine glucose
Haematuria

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55
Q

What is oliguria?

A

Low urine output

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56
Q

What is anuria?

A

Lack of urine

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57
Q

What is polyuria?

A

Frequent uria

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58
Q

How are nitrogenous wastes produced?

A

Produced from the catabolism of amino acids and nucleic acids

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59
Q

How are nitrogenous wastes eliminated from the body?
(2)

A

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

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60
Q

What is urea called in US?

A

Blood urea nitrogen

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61
Q

How is urea excreted?
(3)

A

Filtered at glomerulus

40% is reabsorbed

More is reabsorbed if the rate of tubular flow is slow (due to renal hypoperfusion)

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62
Q

What might increase plasma urea?
(7)

A

GI bleed
Trauma
Renal hypoperfusion
Decreased ECFV
Acute renal impairment
Chronic renal disease
Post-renal obstruction (calculus tumour)

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63
Q

What is plasma creatinine?
(3)

A

Waste product of muscle metabolism
Increases in concentration as GFR decreases
Not proportional to renal damage

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64
Q

When is urea excretion high

A

When dehydrated

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65
Q

What renal test results indicates dehydration?

A

Normal creatinine but high urea

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66
Q

Is creatinine proportional to renal health?

A

No its not proportional to renal damage

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67
Q

What is important about plasma creatinine levels?

A

The change in values within an individual patient is usually more important than the absolute value

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68
Q

What happens to plasma creatinine in chronic renal disease?
(2)

A

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

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69
Q

What is normal creatinine levels proportional to?
(2)

A

Normal creatinine is proportional to muscle mass

Men have a higher RR than females, muscly men have a higher range than females

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70
Q

What does it mean if plasma creatinine value doubles

A

This means GFR and renal function has probably fallen to half of normal

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71
Q

What is uric acid also called

A

Urate

72
Q

What is uric acid/urate
(2)

A

The end product of purine metabolism

The kidneys excrete two-thirds of uric acid produced daily, remaining one third is excreted in stool

73
Q

Where do we get purines from?
(2)

A

Dietary sources such as organs (liver, kidney), sweetbreads, sardines, anchovies, lentils, muschrooms, spinach and asparagus

Get it from the breakdown of body proteins

74
Q

What happens if uric acids build up?
(3)

A

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

75
Q

What is the principle behind GFR measurement

A

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

76
Q

What is renal clearance?

A

The ability of the kidneys to remove molecules from plasma and excrete those molecules in the urine

Renal clearance = (filtration + secretion) - reabsorption

77
Q

Write a note on GFR
(5)

A

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

78
Q

What is used to estimate GFR

A

Urinary clearance of filtration markers

79
Q

What are two characteristics of ideal filtration markers?

A

Freely filtered
Neither secreted nor absorbed by kidney tubule

80
Q

What is the gold standard exogenous substance used to estimate GFR

A

Inulin (found in garlic)
IV infusion
But difficult to assay

81
Q

Give two substances other than inulin used to estimate GFR

A

Cr51 - EDTA
I^125 - iothalamate

82
Q

Write a note on how creatinine clearance is used as a marker of GFR
(5)

A

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

83
Q

Why is creatinine clearance so hard for subjects to measure?

A

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

84
Q

What are the units for creatinine clearance

A

Mls/min

85
Q

What is Ucreat

A

Urine creatinine concentration (umol/L)

86
Q

What is Pcreat

A

Plasma creatinine concentration (umol/L)

87
Q

How does a healthy person’s creatinine clearance compare to their GFR

A

In healthy it is 10-30% higher than GFR

88
Q

What might increase the tubular secretion of creatinine

A

Chronic renal disease

89
Q

What might inhibit the tubular secretion of creatinine

A

Drugs e.g. salicylate, cimetidine

90
Q

Overall why is creatinine clearance an unreliable test

A

Problems with collection
Drugs or chronic renal disease can affect GFR

91
Q

What are the four main tests carried out for renal function and comment on if they are practical or not?

A

Glomerular filtration rate = impractical
Creatinine clearance = unreliable
Plasma creatinine = specific but insensitive
Plasma urea = subject to problems

92
Q

What is eGFR and how is it worked out
(3)

A

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

93
Q

Give an example of an eGFR equation

A

Modification of Diet in Renal Disease Study = MDRD equation

CKD-EPI Equation -> Chronic Kidney Disease Epidemiology Collaboration

94
Q

Compare the CKD-EPI and GFR equations

A

The CKD_EPI equation was shown to perform better than the MDRD equation espiecially at higher GFR, with less bias and greater accuracy

95
Q

Define renal failure

A

A deterioration in renal function leading to a complex of symptoms and signs

96
Q

What are the two signs of renal failure

A

Azotaemia
Uraemia

97
Q

What is azotaemia

A

Increase in nitrogenous substances e.g. urea and creatinine

98
Q

What is uraemia

A

Symptoms of confusion etc associated with azotaemia

99
Q

What are the two types of kidney disease

A

Acute Kidney Injury
Chronic Kidney Disease

100
Q

What is the difference between acute kidney injury and chronic kidney disease

A

AKI = quick onset, occurs over hours/days

CKD = progressive loss in kidney function over a period of months or years

101
Q

What was acute kidney injury previously called

A

Acute renal failure (ARF)

102
Q

How is acute kidney injury defined?

A

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

103
Q

What generally causes acute kidney injury
(4)

A

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

104
Q

What may acute kidney injury lead to?
(5)

A

Metabolic acidosis
High potassium levels
Uraemia
Changes in body fluid balance
Effects on other organs systems, including death

105
Q

What risk is increased later in life by having suffered from AKI

A

Risk of chronic kidney disease is greatly increased

106
Q

How is AKI managed

A

Treatment of the underlying cause and supportive care, such as renal replacement therapy

107
Q

How many stages to chronic kidney disease are there?

A

Five stages

108
Q

How is chronic kidney disease classified?

A

Based on measured or estimated GFR

109
Q

What GFR indicates stage 1 CKD

A

GFR of more than 90

110
Q

What GFR indicates stage 5 CKD

A

GFR less than 15

111
Q

What is stage 1 CKD

A

Kidney damage (protein in urine) and normal GFR

112
Q

What is stage 2 CKD

A

Kidney damage and mild decrease in GFR

113
Q

What is stage 3 CKD

A

Moderate decrease in GFR

114
Q

What is stage 4 CKD

A

Severe decrease in GFR

115
Q

What is stage 5 CKD

A

Kidney failure - End stage renal disease (dialysis or kidney transplant needed)

116
Q

What are the signs and symptoms of renla failure
(6)

A

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

117
Q

What happens when extracellular fluid volume falls

A

Blood pressure falls

118
Q

What happens when blood volume and pressure is really low

A

Not adequate flow to brain and other organs

119
Q

Why do the kidneys work with the cardiovascular system?

A

To maintain pressure in acceptable range

120
Q

What causes the production of renin
(3)

A

Low blood pressure
Low blood volume
Low sodium

121
Q

What is angiotensinogen converted into and by what?

A

Angiotensinogen is converted into angiotensin I by renin

122
Q

What is angiotensin I converted into and by what

A

Angiotensin I is converted into Angiotensin II by angiotensin converting factor

123
Q

What blocks angiotensin converting enzyme

A

ACE-I

124
Q

What are ACE-Is?

A

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

125
Q

What does angiotensin II act on

A

Systemic vasoconstriction

Renal vasoconstriction

126
Q

What affects does angiotensin II have on the kidney
(2)

A

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

127
Q

What affects does aldosterone have?
(3)

A

Increases sodium/potassium exchange

This results in increased retention of sodium and H2O but the increased loss of potassium ions

This increases blood pressure

128
Q

How is total blood volume measured

A

300 milliosmoles/L

129
Q

What are milliosmole?

A

Measure of osmolarity: the total number of dissolved particles (glucose, protein, etc) per liter of solution

130
Q

What is sodium
(4)

A

Na
Major extracellular cation

10 mmol/L intracellularly
140 mmol/L extracellularly (blood)

131
Q

How much sodium should we intake a day?

A

100-200 mmol/day

132
Q

How much sodium is excreted in the faeces, sweat, renal?

A

10 mmol/day in faeces
10-20 mmol/day in sweat
The rest matches intake

133
Q

Describe the relationship between sodium and water

A

Where sodium goes, water follows

134
Q

Write about the regulation of water
(2)

A

Thirst regulates input
Anti-diuretic hormone (vasopressin) regulates water output

135
Q

Write a note about the regulation of sofium

A

Renin-angiotensin-aldosterone (RAA)
Natriuretic peptides
Both regulate output

136
Q

What is antidiuretic hormone ADH also called?

A

Vasopressin

137
Q

What is Antidiuretic hormone?
(4)

A

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

138
Q

What does ADH control

A

Renal water excretion

Its also a potent vasoconstrictor

139
Q

What does low ADH mean?

A

High urine volume
Low urine osmolality

140
Q

What does high ADH mean?

A

Low urine volume
High urine osmolality

141
Q

Give one cause of increased osmolality

A

Hypernatraemia

142
Q

What may cause hypernatraemia

A

Dehydration

143
Q

What is RAA

A

Renin-angiotension-aldosteron

144
Q

What causes release of renin

A

Low renal perfusion

145
Q

What causes low renal perfusion?

A

Hypovolaemia
Heart failure
Shock

146
Q

What does Angioitensin II do>

A

Releases aldosterone from adrenal gland

147
Q

What does aldosterone do?

A

Acts in the proximal tubule
Reabsorbs sodium and excretes potassium

i.e. it controls urine sodium excretion

148
Q

What would ACE inhibitors be used to treat?

A

Hypertension

149
Q

What do diuretics do?
(5)

A

Excrete more urine
Lower blood volume
Lower blood pressure
Excessive potassium loss (important for muscles)
Many different kinds

150
Q

How do the kidneys help maintain normal blood pH
(2)

A

Kidneys help with response to alkalosis or acidosis

They excrete H+, reabsorb bicarbonate indirectly through carbonic anhydrase

151
Q

What buffers are found in blood

A

NH3 (ammonia)

PO4^-3

152
Q

Explain in your own words how the kidneys keep the blood at the correct pH
(3)

A

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+

153
Q

How does the body maintain ion balance

A

Key ions kept normal via balance of dietary intake and urine loss

Sodium, Potassium and Calcium well regulated

154
Q

What are electrolytes

A

Substances that become ions in solution and acquire the capacity to conduct electricity

155
Q

Why is electrolyte balance important?

A

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

156
Q

What are electrolytes related to in the body?
(4)

A

Fluid balance
pH
Membrane potential
Tissue excitability

157
Q

List the six important electrolytes

A

Sodium
Potassium
Chloride
Bicarbonate

Calcium
Phosphate (these two are for bone, muscle contraction etc)

158
Q

Write a note on sodium
(3)

A

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

159
Q

Write a note on potassium
(3)

A

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

160
Q

Write a note on chloride
(2)

A

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

161
Q

Write a note on bicarbonate
(3)

A

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

162
Q

Describe the reabsorption of sodium
(4)

A

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

163
Q

How is sodium absorbed by the distal tubule

A

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

164
Q

What causes hypernatremia

A

Excess water loss (severe vomiting, diarrhea, or polyuric state)

Increased renal sodium conservation

165
Q

What causes hyponatremia

A

Decreased tubular reabsorption as a result of inappropriate diuretic therapy, primary or secondary hypoaldosteronism

166
Q

Describe the absorption of potassium
(3)

A

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

167
Q

What may cause hyperkalaemia

A

Due to transcellular shift intake in intake, and or decrease in output

168
Q

What may cause hypokalaemia

A

Increased loss, transcellular shift, or decreased intake of potassium

169
Q

What are some complications of untreated hypokalaemia or hyperkalaemia?

A

High morbidity and mortality

170
Q

What is the chemical formula for the bicarbonate ion

A

HCO3-

171
Q

Write a note on the bicarbonate ion
(3)

A

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

172
Q

What increases bicarbonate concentration of serum?
(2)

A

Increases in metabolic alkalosis

In compensated respiratory acidosis

173
Q

What decreases serum bicarbonate?
(2)

A

Metabolic acidosis

Compensated respiratory alkalosis

174
Q

Write a note on chloride (Cl-)
(3)

A

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

175
Q

What happens in renal insuffiency?
(4)

A

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

176
Q

What is dialysis
(2)

A

A machine used for the treatment of renal insufficiency

Molecules diffuses through selectively permeable membrane

177
Q

What is haemodialysis

A

This removes solutes (waste particles) and fluid from the blood across a semipermeable membrane in a filter (dialyzer)

2.2 Clinical Chemistry (28 decks)

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