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Module 104 - Nutrition, metabolism & excretion > T2 L7 Measurement of renal function > Flashcards

T2 L7 Measurement of renal function Flashcards

1
Q

What are the 2 reasons to measure renal function?

A

1) Identify a renal impairment in a patient

2) Modification of dosages of drugs which are cleared by the kidneys

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2
Q

What patients are at risk of developing renal failure?

A 
Extremes of age: neonates & elderly
Polypharmacy
Specific disease states
Patients receiving long-term analgesia
Transplant patients
Drug therapy
Patients undergoing imaging procedures
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3
Q

What specific disease states increase the risk of developing renal failure?

A 
Hypertension
Diabetes
Chronic heart failure
Rheumatoid arthritis
Renal disease
Recurrent urinary tract infections
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4
Q

Why are transplant patients at increased risk of developing renal failure?

A

They are given anti-rejection drugs which can affect the liver & kidney function

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5
Q

Why are patients undergoing imaging procedures at increased risk of renal failure?

A

The radiocontrast agents can be nephrotoxic

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6
Q

What methods are used to monitor a patient’s renal function?

A

Patients clinical condition - clinical assessment & use of bedside clinical data
Modern imaging techniques
Biochemical data

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7
Q

What signs are symptoms are shown if fluid balance is affected?

A

Oedema

Breathlessness

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8
Q

What signs are symptoms are shown if electrolyte regulation is affected?

A

Abnormal ECG - absent P waves, broad QRS complex, peaked T waves

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9
Q

What signs are symptoms are shown if EPO production is affected?

A

Pallor

Fatigue

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10
Q

What signs are symptoms are shown if vitamin D3 is affected?

A

Osteomalacia

Bone pain

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11
Q

What signs are symptoms are shown if excretion is affected?

A

Raised blood urea & creatinine concentrations

Pruritis

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12
Q

What signs are symptoms are shown if acid-base balance is affected?

A

Low blood pH & bicarbonate levels

Deep & rapid respiration

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13
Q

What bedside clinical data can be used to assess a patient’s renal function?

A

Weight charts
Fluid balance charts
Degree of oedema
Results of urine dipstick testing - urinalysis for protein, blood, glucose

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14
Q

What are some types of renography?

A

Gamma camera plana scintigraphy
Positron emission tomography (PET)
Single photon emission computerised tomography (SPECT)

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15
Q

What is biochemical data useful for?

A

Identifying renal impairment
Evaluation of the ability of the kidneys to handle water & solutes
Modifying dosages of drugs which are cleared by the kidneys

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16
Q

What would an ideal marker of kidney function be?

A

Naturally occurring molecule
Not metabolised
Only excreted by the kidney
Filtered by not secreted or reabsorbed by the kidney

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17
Q

Why are plasma or serum creatinine late markers?

A

The kidneys have to lose 50% or more of their function for these to show up

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18
Q

What is plasma creatinine?

A

Breakdown product of creatine phosphate in the muscle
Generally produced at a constant rate
Filtered at glomerulus with some secretion into proximal tubule

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19
Q

What is the normal range of plasma creatinine in the plasma?

A

40-1200umol/L

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20
Q

What can increase plasma creatinine?

A

Large muscle mass
Dietary intake
Drugs which interfere with analysis such as methyldopa, dexamethasone, cephalosporins
Drugs which inhibit tubular secretion - cimetidine, trimethoprim, aspirin
Ketoacidosis - affects analysis
Ethnicity - higher creatine kinase activity in black population

21
Q

What can decrease plasma creatinine?

A 
Reduced muscle mass such as elderly
Cachexia / starvation
Immobility
Pregnancy
Severe liver disease - liver is a source of creatinine.
22
Q

What is plasma urea?

A

Indicator of renal function & failure
Liver produces urea in the urea cycle as a waste product of protein digested
Filtered at glomerulus, secreted & absorbed in tubule

23
Q

What is the normal range of serum urea?

A

2.5-7.5mmol/L

>20mmol/L indicates moderate to severe renal failure

24
Q

What can increase blood urea nitrogen?

A 
High protein diet
Hypercatabolic conditions - severe infections, burns, hyperthyroidism
Gastrointestinal bleeding
Muscle injury
Drugs
Hypovolaemia
25
Q

What can decrease blood urea nitrogen?

A

Malnutrition
Liver disease
Sickle cell anaemia due to increased GFR
SIADH

26
Q

What does it mean if a substance is filtered at the glomerulus but not reabsorbed?

A

Excretion rate = rate it was filtered

Freely filtered but not reabsorbed or secreted

27
Q

What does it mean if a substance is filtered and some of the filtered portion is reabsorbed?

A

Excretion rate = filtration rate - reabsorbed
Typical of electrolytes
Freely filtered & partly or mostly reabsorbed

28
Q

What does it mean if a substance is filtered & completely reabsorbed?

A

No excretion
Glucose and amino acids
Freely filtered & fully absorbed

29
Q

What does it mean if a substance is primarily secreted into the tubule?

A

Substance is rapidly & effectively cleared such as PAH

Freely filtered, not reabsorbed, full secreted

30
Q

What is clearance?

A

Volume of plasma completely cleared of a given substance in unit time
Virtual volume of blood that would be totally cleared of a solute in a given time
Solute comes from blood perfusing kidneys

31
Q

What 3 functions does renal clearance provide information about?

A

Glomerular filtration
Tubular reabsorption
Tubular secretion
Rate at which kidneys excrete solute into urine = rate at which solute disappears from blood plasma

32
Q

What are the drawbacks of measuring renal clearance?

A

It is a measurement of overall nephron function
Gives the sum of all transport processes occurring along nephrons
No information about precise tubular sites of mechanisms of transport

33
Q

What is the glomerular filtration rate?

A

Rate at which filtrate is produced by the kidneys
Can be estimated by measurement of clearance of creatinine.
More accurate estimation provided by measurement of inulin clearance which is filtered but not secreted into tubule.

34
Q

What is inulin?

A

Plant polysaccharide

35
Q

Why is inulin clearance used for measurement of GFR?

A

It is freely filtered so plasma & tubular concentrations are the same
It is not secreted or reabsorbed
Rate of excretion in urine = rate of filtration by kidneys

36
Q

What does it mean if a substance has a clearance greater than inulin?

A

It must also be being secreted

37
Q

What does it mean if a substance has a clearance less than inulin?

A

It is being reabsorbed or not filtered freely at the glomerulus

38
Q

What are the drawbacks of using inulin to measuring GFR?

A

Inulin must be administer by IV to get relatively constant plasma or serum levels
Chemical analysis of inulin in serum & urine is technically demanding
Could use radiolabelled compounds instead - these may bind to proteins & distort results

39
Q

How are problems of IV infusion of GFR marker avoided?

A

By using an endogenous substance with inulin like properties such as creatinine

40
Q

Describe the results from measuring creatinine clearance

A

Filtered at glomerulus & secreted into proximal tubule
Using equation gives over-estimate of GFR by 20%
Colorimetry methods used to measure creatinine under-estimate clearance by 20% so the euros cancel each other out

41
Q

What are the benefits of using creatinine clearance?

A

Cheap
Easy
Reliable
Avoids IV infusion - only needs venous blood & urine samples

42
Q

When should you measure creatinine clearance?

A

Before breakfast

43
Q

How do you adjust the creatinine clearance to account for body surface area?

A

Corrected creatinine clearance = (measured CrCl x 1.73) / BSA (body surface area in m2)

44
Q

What are the 2 formulas used to estimate GFR using serum creatinine?

A

Cockcroft-gault formula

MDRD (modification of diet in renal disease) formula

45
Q

What are the estimated GFR ranges?

A

Males: 97-137ml/min
Females: 88-128ml/min

46
Q

Why is the clearance of PAH used to estimate RPF?

A

It is not normally present in the blood

When PAH is given almost all is cleared from the kidney in one passage

47
Q

What happens to the PAH that by-passes the tubule?

A

It travels from the efferent arteriole –> peritubular capillaries –> venous renal blood –> not secreted

48
Q

What are biomarkers of renal disease?

A

Indicators of renal function such as serum creatinine or BUN only increase after a significant loss of renal function
Urinary albumin/protein excretion can be used as an indicator of chronic kidney disease

49
Q

What proteins are released into the urine that are used for biomarkers?

A 
Kidney injury molecule
Interleukin
Fatty-acid binding proteins
Neutrophil gelatinise-associated lipocalin
Cystatin C

Module 104 - Nutrition, metabolism & excretion (31 decks)

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