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Renal Biochemistry > Biochemical Assessment of Renal Function > Flashcards

Biochemical Assessment of Renal Function Flashcards

1
Q

Describe the kidneys?

A

paired retroperitoneal organs, bean-shaped,
weighing 120-170g

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2
Q

Describe the resting cardiac output that flows to the kidneys?

A

25% - 180L of filtrate but only 1-2L of
urine produced/day

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3
Q

What is the vasculature of the kidneys?

A

supplied by renal artery, drained by the renal
vein

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4
Q

Innervation of the kidneys?

A

renal plexus

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5
Q

What is the functional unit of the kidney?

A

nephron

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6
Q

Describe the structural components of the nephron?

A
  1. Glomerulus
  2. Proximal convoluted tubules
  3. Loop of Henle
  4. Distal convoluted tubules
  5. Collecting duct
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7
Q

Describe the functions of the different parts of the nephron?

A
  1. glomerulus - filtration
  2. proximal tubule - where main reabsorption occurs
  3. distal tubule - secretion
  4. collecting duct - water reabsorption
  5. loop of Henle - concentration of filtrate
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8
Q

What are the 3 basic renal processes?

A
  1. Glomerular filtration
  2. Tubular reabsorption
  3. Tubular secretion
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9
Q

What are the endocrine functions of the kidneys?

A
  1. synthesis of hormones - 1,25-dihydroxyvitamin D3, renin and angiotensin and erythropoietin
  2. response to hormones
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10
Q

What are the excretory function of the kidneys?

A
  1. Protein metabolism
  2. NA metabolism
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11
Q

What are the homeostatic functions of the kidney?

A
  1. acid-base (isohydria)
  2. electrolyte (isoionia)
  3. fluid (isovolumia)
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12
Q

What is the metabolic function of the kidneys?

A

Gluconeogenesis during starvation

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13
Q

What does normal renal function depend on?

A
  1. number of functioning nephrons
  2. blood supply
  3. hormone secretion and feedback
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14
Q

Describe acute renal failure?

A

rapid loss of renal function

  • usually but not always oliguric : (<400ml/24hr)
  • retention of urea, creatinine, H+, K+, proteinuria
  • potentially reversible
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15
Q

What is polyuria?

A

passing abnormally large amounts of urine

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16
Q

What is anuria?

A

failure of the kidneys to produce urine

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17
Q

What is oliguria?

A

urine output below normal

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18
Q

What is the cause of pre-renal ARF?

A

reduced renal perfusion
- blood loss, hypovolaemia

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19
Q

What is the cause of post-renal ARF?

A

ureteric/urethral obstruction
- stones or malignancy

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20
Q

What is the cause of renal ARF?

A

intrinsic kidney tissue damage
- glomerulonephritis, nephrotoxins

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21
Q

Describe chronic renal failure?

A

progressive irreversible destruction of
kidney tissue
- major effects of CRF are due to loss of
functional nephrons
- some patients may be asymptomatic until very
low levels of GFR
- most patients will require dialysis or
transplant

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22
Q

What is the purpose of renal functions tests?

A
  1. detecting presence of renal disease.
  2. assessment of progression of renal disease
    - less valuable in determining the causes
    of renal disease
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23
Q

What are the early indicators of chronic renal failure?

A
  1. Diabetes
  2. High blood pressure
  3. Cardiovascular disease
  4. Heamaturia or proteinuria
  5. Chronic use of known nephrotoxic agents
  6. Seriously sick patients
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24
Q

What are the types of renal function tests?

A
  1. glomerular function
  2. tubular function
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25
Q

What are glomerular function tests?

A

a measure of the filtration rate (GFR)
- index of number of functioning nephron

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26
Q

How are glomerular function tests done?

A

clearance tests : [urine in sample] & [plasma in sample]

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27
Q

What are the characteristics of the substances measured in glomerular function tests? i.e. an ideal marker

A
  1. endogenous substance
  2. freely filtered by the glomerulus
  3. not metabolized by the tubules
  4. [substance] remains constant during the period of urine collection
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28
Q

What is the clearance equation?

A

clearance = [urine] x flow rate/[plasma]

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29
Q

What is the gold standard for measuring GFR?

A

urinary inulin clearance
- inulin has all the properties of an ideal marker
NB: inulin - plant CHO

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30
Q

What is creatinine?

A

a product of energy (ATP) yielding reactions made by muscles as part of regular everyday activity

  • phosphocreatine in muscles
  • meets most of the criteria for an ‘ideal’ substance
  • up to 10% Cr is actively secreted into the urine by renal tubules
31
Q

What is the issue with a 24 hour timed urine collection period?

A

delays the availability of the result and increases the potential for collection errors

32
Q

Which time period for urine collection is better: 24 or 12 hours?

A

they are both accurate

33
Q

What are the problems with using Creatinine Clearance?

A

as the GFR falls, Cr Cl overestimates the true GFR because it is also secreted by the peritubular capillaries
- overestimates the GFR by 10 - 20%

34
Q

What is the reference range for creatinine clearance?

A

~120ml/min in adults (gender dependent)
- decreases with age (6.5ml/min/1.73m2 for
each decade of life)

35
Q

What is plasma creatinine?

A

the amount of creatinine in your blood
- an increased level may be a sign of poor kidney function

36
Q

When is plasma creatinine used?

A

only useful when GFR is very low
- levels out of reference range when GFR has declined by
more than 50%

37
Q

Plasma level are affected by?

A
  1. Muscle mass
  2. Diets
  3. Exercise
  4. Drugs
38
Q

What is eGFRcr?

A

measures how much blood these filters clean every minute based on your body size - calculated GFR : when formulae have been used

39
Q

What is the Cockcroft and Gault equation?

A

Ccr = (140 - age) x weight (kgs) x (0.85 if pt female)/0.81 x serum [creatinine]

40
Q

What is MDRD study equation?

A

GFR (ml/min/1.73m2 = 175 x [Crs (micro mol) x0.0113] - 1.154 x [age] - 0.203 x [1.212 if black] x 0.742 if female]

  • takes into account ethnicity but does not incorporate weight
41
Q

What is the normal estimate of eGFR?

A

>60ml/min/1.73m2

42
Q

Describe isotope labelled clearance?

A
  • the most accurate, very expensive
  • 99m Tc or 51Cr-EDTA
  • 2 samples taken 1-3hrs after administration
  • GFR calculated from plasma clearance
43
Q

Urea is formed from?

A

AA ⇢ NH3 ⇢ urea

44
Q

Describe plasma urea (BUN)?

A
  • inferior to plasma [creatinine] as a measure of renal function - 50% of filtered urea is reabsorbed, more if flow rate decreases (dehydration) - affected more by diet than [creatinine]
45
Q

What does a creatinine > 20 indicate?

A

pre or post renal azotemis

46
Q

What is glomerular proteinuria?

A

Abnormal permeability of the glomerular capillaries to protein

47
Q

What is selective glomerularlis?

A

only intermediate-sized proteins leak (<100kDa)

48
Q

What is non-selective glomerular proteinuria?

A

range of differently sized proteins including larger proteins (Ig)

49
Q

What is microalbuminuria?

A

small quantities of albumin in the urine ranging from 30 - 300 mg/24 hrs or spot urine 30- 300mg/L (2/3 visits over a 4 month period)

50
Q

What are the levels of spot urine albumin in males and females?

A

Creat >2.5mg/mmol (male) or 3.5mg/mmol (female)

51
Q

Microalbuminuria is an indication of?

A
  1. diabetes nephropathy
  2. vascular endothelial dysfunction
  3. hypertension
52
Q

Describe the autoantibody test for renal function tests?

A

titres against self-destructive ab

  • Anti-GBM + ANA
53
Q

What are tubular function tests?

A

chemical analysis of urine

54
Q

Renal tubular disorders may affect?

A
  1. ability to concentrate urine
  2. ability to excrete an appropriately acidified urine
    1. reabsorption of aa, gluc, phosp etc
55
Q

What is urinalysis?

A

screening tool that tests for physical properties using dipstics

56
Q

What physical properties are tested during urinalysis?

A
  1. Sg and osmolality
  2. pH, WBC
  3. Glucose
  4. Protein
  5. Ketones
  6. urobilinogen
  7. Nitrites
57
Q

Describe the osmolality in a healthy person?

A

osmolality of urine is >3x the osmolality of serum (mmol/kg)

58
Q

What do renal concentrating tests measure?

A

[urine] produced in response either to fluid deprivation or to IM injection of vasopressin (DDAVP).

59
Q

Describe the process of fluid deprivation?

A
  1. Starting at 10pm, no fluid
  2. Urine/blood samples collected between 8am- 3pm the next day; pt weighed every 2hrs
  3. If weight loss of 3-5% of total body weight occurs, test should be stopped.
60
Q

What is the normal reaction to fluid deprivation?

A
  1. No rise in plasma osmolality (285-295)
  2. Rise in urine osmolality to > 800
61
Q

Describe the process of the DDAVP test?

A
  1. Pt allowed to drink a moderate amount of water after the fluid deprivation tests
  2. used to identify type/cause of DI
  3. IM injection of DDAVP given
  4. samples collected hourly for the next 3hrs
62
Q

Describe the interpretation of the DDAVP test?

A

+ response = diabetes insipidus of HP origin

  • response = nephrogenic diabetes insipidus
63
Q

What are urinary acidification tests?

A

tests that assess the capacity of the tubules to produce an acid urine after induction of metabolic acidosis - useful in diagnosis of RTA

64
Q

Describe the use of ammonium chloride in urinary acidification tests?

A
  1. 7g NH4Cl/100ml administered by mouth
  2. hourly collection of urine & arterial blood in the next 5hrs
  3. If urine pH does not fall below 5.3 in one sample ⇒ RTA type 1
65
Q

What is reabsorptive proteinuria?

A

LMW proteins appear in urine (<70kDa)

66
Q

What is secretory tubular proteinuria?

A
  1. Tamm-Horsfall protein (120kDa)
  2. N-acetyl β-glucosamidase
67
Q

What is the interpretation of tubular proteinuria?

A

urine protein of >2.5g/day – Nephrotic syndrome

68
Q

Describe Glycosuria, aminoaciduria & phosphoturia?

A
  1. described as Fanconi syndrome (acidosis is present)
  2. urine gluc >5mmol/L when plasma gluc is normal
  3. in children need to screen for IEM
69
Q

How do you screen for IMD with reducing sugars?

A

using Clinitest tablets (except sucrose)

⇒ chromatography

70
Q

How do you screen for IMD with amino aciduria?

A
  • by TLC
  • confirmed with HPLC
71
Q

What are renal stones?

A

relative insolubility of urine constituents in water leading them to crystallize out – calculi

  • radiological examination required to localize the stone, pts ‘cut for stone
72
Q

What are the predisposing factors of renal stones?

A
  1. dehydration
  2. changes in urine pH
  3. specific microorganisms
72
Q

What are the predisposing factors of renal stones?

A
  1. dehydration
  2. changes in urine pH
  3. specific microorganisms
73
Q

State the metabolic and endocrine disturbances in chronic renal failure?

A
  1. Retention of nitrogenous waste products (uraemic toxins)
  2. Na, K & water imbalances
  3. Acid-base disturbance
  4. Ca2+,PO 4- , Mg2+& renal osteodystrophy
  5. Gonadal function
  6. Anaemia

Renal Biochemistry (1 decks)

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