Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Renal and Urology > Disorders of Renal Function > Flashcards

Disorders of Renal Function Flashcards

1
Q

Describe renal clearance

A

-Rate at which a substance is removed from the blood stream (theoretical)
=a(urine)= c(urine) x v(urine)
=amount of ion cleared per minute= conc of urine x volume of urine
-Volume of plasma completely cleared of a substance per unit time
=V(plasma)= c(urine) . V(urine)/ c(plasma)
=clearance of ion from plasma= amount of ion cleared per min/ concentration of ion in plasma

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is GFR?

A
  • Volume filtered by glomeruli, per unit time

- Clearance (for a substance that is completely lost from the plasma to the urine)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do we calculate GFR?

A

-GFR= UO + V(vein)/min
=UO= V(ureter) per min
*Conc V(vein)= 0 as substance completely lost from plasma
-GFR= c(urine) . UO/ c(plasma) mL/min

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the conditions for the substances measured to calculate GFR?

A
  • Must not alter GFR
  • Freely filtered at glomerulus
  • Not reabsorbed/ actively secreted in nephron
  • Not metabolised/ produced by kidney
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why do we measure GFR?

A
  • Provides an assessment of global renal function
  • Pathology causing loss/ damage to glomeruli affects kidney generally- GFR loss correlated with general loss of function
  • Guides management in CKD
  • Rate of decline predicts need for renal replacement therapy
  • Used to guide dosing of potentially toxic (renally cleared) drugs
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Examples of exogenous substances used in measuring GFR

A

*invasive and time-consuming so rarely used

-Inulin (fructose polymer, MW 5 kDa)
=Continuous IV infusion combined with timed urine collections
=Not generally used outside research

-Radioisotope tracers
=15Cr-EDTA, or 125I-iothalamate
=Single injection, followed by serial blood tests
=Again rarely used outside research

-Iohexol
=Non-radioactive contrast agent
=Single injection, followed by serial blood tests
=Sometimes used in paediatrics (unusually low muscle mass)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Examples of endogenous substances used in measuring GFR

A

-Creatinine
=Small molecule (113 Da)
=Produced at relatively constant rate (muscle metabolism)
=Some active tubular secretion
=Long-established role in GFR measurement

-Cystatin C
=Small protein (13kDa), inhibitor of proteases
=Produced by all nucleated cells
=No significant tubular secretion/ absorption
=10-20x more expensive to measure (than creatinine)
=Relatively new method of measuring GFR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe creatinine clearance

A

-Plasma creatinine measurement
-24hr urine collection
=Inconvenient for patient, inaccurate (not complete/ mis-timed), imprecise
-At very low GFR further inaccuracy
=less creatinine filtered, amount creatinine secreted proportionally larger

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Can we measure plasma creatinine alone?

A
  • Reciprocal relationship with GFR

- But very large inter-individual differences (muscle mass, age, gender, ethnicity)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the Cockcroft-Gault equation?

A

-Plasma creatinine
-Requires weight, age, sex
-Often used to adjust dosing for renally-excreted drugs with potential toxicity
-eGFR= (140-age)(weight)/ (Crx)
=x for men= 0.81, women= 0.85

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the MDRD?

A
  • Modified Diet in Renal Disease

- Equation only applicable to those with low GFR, shown to be inaccurate at “healthy” GFR (and very low GFR)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is EPI?

A

-Updated eGFR equation by CKD Epidemiology Collaboration
-Generates more reliable eGFR at 60-90 ml/min/1.73m2
-May mean that progressive renal disease spotted earlier
Recommended by NICE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When do the equations lose applicability?

A
  • Children, pregnancy, very elderly?
  • Muscle mass extremes (frail, amputee, heavily built)
  • Rapidly-changing renal function (overestimate in acute)
  • Very low GFR
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does eGFR contribute to classification of CKD?

A
  • CKD= progressive and irreversible loss of kidney function caused by irreversible damage to increasing numbers of nephrons
  • Early treatment delays progression
  • Classification also includes urinary albumin: creatinine ratio (ACR)
  • Diagnosis usually requires eGFR consistently to be less than 60 mL/min/1.73m2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What can CKD be diagnosed above 60mL/min/1.73m2?

A
  • Persistent proteinuria/ microalbuminuria
  • Haematuria
  • Renal anatomical/ genetic abnormality (biopsy-proven GN, or PKCD)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is Acute Kidney Injury (AKI)?

A

An abrupt loss of renal function, commonly characterised by acute:
-Oliguria
-Increases in plasma urea and creatinine
Often accompanied by a loss of in ability to regulate water, electrolyte and acid-base balance
*Acute on chronic kidney injury refers to acute insult on background existing renal impairment

17
Q

What is the clinical criteria for detecting AKI?

A

-Rely on creatinine and UO
-Increase in plasma creatinine of >/26 umol/L within 48 hours, >/50% in the last 7 days
=requires establishing creatinine baseline from previous results so early stage of AKI missed
-UO <0.5mL/kg/hr for >6hrs in adults (8 in children)

18
Q

What are AKI e-alerts?

A

-Lab-computer based algorithm to:
=Determine creatinine baseline
=Calculate magnitude of creatinine rise

19
Q

What are the functions of the renal tubules?

A
  • Essential for electrolyte, water and acid-base homeostasis
  • Reabsorption of water that occurs in distal tubules allows urine to be variably concentrated or diluted, according to need
  • Distal tubules also perform “fine-tuning” of electrolyte homeostasis
20
Q

Describe acid-base homeostasis

A
  • Kidneys play important role in maintaining plasma H+ concentration within tight limits
  • Responsible for excreting H+, re-absorbing and regenerating bicarbonate
    (plasma. ECF bicarbonate buffer)
  • Urine usually significantly more acidic than plasma (5.5 vs 7.35-7.45)
  • Any significant damage to tubules can impair urine acidification
  • However overt rise in urine pH is relatively rare
21
Q

What is Renal Tubular Acidosis (RTA) Type 1?

A
  • Can lead to pH (urine)>5.5
  • Distal tubular cells unable to secrete H+ (abnormally permeable to H+)
  • Many possible causes: autoimmune, paraproteinemia, nephrocalcinosis
22
Q

What is the Ammonium chloride loading test?

A
  • Used to confirm suspected RTA type 1
  • NH4Cl administration leads to metabolic acidosis (so rarely used)
  • Of pH urine >5.5 persists them RTA type 1 confirmed
23
Q

Describe electrolyte homeostasis

A

-Imbalances of plasma electrolytes may be renal in origin
-Renal causes may be identified/ excluded by investigation of plasma and urine
=Hypokalaemia- causes: renal loss, GI loss (vomiting/diarrhoea), shifts into cells
=Spot urine K+ <20mmol/L usually excludes renal loss

24
Q

How can spot urine tests be more efficient?

A
  • 24hr urine collection
  • Measure creatinine (or osmolarity) to correct for variability in urine conc. and blood concentration (fractional excretion)
25
Q

Describe sodium and fluid balance in the tubules

A

-Plasma sodium more an indicator of fluid balance than total body sodium
=hypernatremia reflects water deficit rather than sodium overload
-135-145 range
-Urine Na+ <30mmol/L= tubules appropriately re-absorbing Na and water (pre-renal failure caused by hypotension)
-Urine Na+ >30mmol/L inappropriate loss- tubular dysfunction/damage/inadequate aldosterone action (intrinsic/ established renal failure caused by untreated pre-renal failure)

26
Q

Describe the urine concentrating ability

A
  • Assessed by measuring urine osmolality (and plasma osmolality for comparison)
  • Loss of urine concentration ability may be accompanied by polyuria
27
Q

How can the relative values of osmolality help diagnosis?

A
  • Chronic renal failure- osmolality urine=plasma= end stage: oliguria
  • Acute tubular necrosis (following pre-renal failure)- urine=plasma- initially oliguric, recovery phase often polyuria
  • Diabetes mellitus- urine=/>plasma= osmotic diuresis, polyuria, high glucose overwhelms urine concentration ability
  • Diabetes insipidus- urine
28
Q

How can the water deprivation test by used in suspected diabetes insipidus

A
  • Involves with-holding fluids over several hours
  • Potentially dangerous, must be monitored very closely (true DI= hypernatremia)
  • DI involves failure of action of vasopressin (or ADH)
  • May be cranial (hypothalamic/pituitary pathology), nephrogenic (tubular problem)
  • Normal response: plasma osmolality static, urine osmolality rises (kidney conc urine)
  • DI: plasma osmolality will rise= urine remains dilute
  • Cranial DI should be responsive to DDAVP (synthetic vasopressin)
29
Q

What is a “Point of Care” test?

A
  • Rapid, simple, convenient, cheap
  • Number of tests varies by manufacturer
  • Readout: coloured strip, or printed report
30
Q

What are the types of Point of Care tests?

A
  • Glucose (diabetes?)
  • Ketones (ketoacidosis?)
  • Protein (albumin)- not as sensitive as lab measurement
  • Blood (detects Hb: calculi, bladder ca., glomerulonephritis)
  • Leukocytes (UTI)
  • Nitrites (produced by nitrate-reducing UTI bacteria)
  • Bilirubin (jaundice)
  • Urobilinogen (absent in cholestatic jaundice)
  • pH, specific gravity (related to osmolality)
31
Q

Describe physiological vs. pathological urine protein levels

A

-Glomeruli prevent passage of most large plasma proteins
-Tubules actively re-absorb/ catabolise low MW proteins
=Increased glomerular permeability- increasing urinary albumin, detectable levels of large MW proteins not normally found in urine
=Decreased tubular protein reabsorption= increased conc. of low MW proteins

32
Q

How is proteinuria detected?

A

-Dipstick testing (not as sensitive as lab testing)
-Lab-based albumin/ protein measurement, sometimes 24hr collection but usually a spot urine using creatinine to adjust for urinary concentration
=Protein: creatinine ratio (PCR)
=albumin: creatinine ratio (ACR)- used to classify CKD

33
Q

What is Microalbuminuria?

A
  • Refers to abnormal level of albumin, usually too low for detection by urine dipstick
  • ACR>3.5,g/mmol in men >2.5mg/mmol in women
  • Important for prevention of significant diabetic nephropathy
  • Can occur transiently (post-trauma, surgery, pyrexia, vigorous physical exercise)

Renal and Urology (43 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions