L80 - Biochemical Investigation of Urogenital Diseases I Flashcards Preview

MBBS I CPRS > L80 - Biochemical Investigation of Urogenital Diseases I > Flashcards

Flashcards in L80 - Biochemical Investigation of Urogenital Diseases I Deck (102):
1

Give examples of reabsorption in kidney?

Glucose, amino acids, electrolytes, proteins

2

What are the 2 metabolic functions of the kidney?

Synthetic: glutathione, glyconeogenesis, ammonia

Catabolic: hormones, cytokines

3

Sequence of intermediates in Vitamin D production? Start from Previtamin D3 in skin.

Previtamin D3 [skin] > Vitamin D3

+ Vitamin D2 and D3 from diet

>> 25-hydroxyvitamin D [liver]

>> 1,25- hydroxyvitamin D [Kidney] (active form)

4

What are some endocrine functions of kidney?

Erythropoietin synthesis, activation of vitamin D,
renin release

5

What is the urine formation rate?

~ 1.5 L/day

1 mL/min

6

What is the normal GFR?

100-125mL/min/1.73m^2

7

Equation for filtration fraction?

filtration fraction is the ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF)

FF = RPF/ GFR

8

What is the normal Hematocrit (Hct) level?

Ratio of the volume of red cells to the volume of whole blood

45% to 52% for men and 37% to 48% for women.

9

What is the normal Renal blood flow rate?

1200 mL/min

~ 20% Cardiac Output

10

How much H2O in glomerular ultrafiltrate is reabsorbed by the kidney??

99%

11

How is Minimal Volume of Urine Water calculated?

= Waste product of metabolism (mOsm/day) / Maximal urinary concentration attainable

12

What is the minimal vloume of urine water excreted per day?

about 400 mL/day

13

Lower than ~ 400 mL/day/ minimal volume of urine water excreted leads to what?

Azotaemia is inevitable with daily Urinary Output < 400 mL

14

Purpose of assessing GFR?

assess the severity and course of renal disease

adjust the dosage of drugs primarily excreted by kidney (or highly nephrotoxic)

15

Describe GFR?

Volume of volume of glomerular filtrate produced by BOTH kidneys per unit time

* glomerular filtrate = Volume of fluid filtered from the kidney glomerular capillaries into the Bowman’s capsule*

16

Define renal clearance?

Clearance of a substance:

The volume of plasma
from which that substance is completely cleared by the kidneys per unit time

17

What are the ideal parameters of a substance used to measure GFR?

- Freely filtered at the glomerulus

- Not reabsorbed by the renal tubules

- Not secreted by the renal tubules or other
organs of the body

- Not synthesized or metabolized by the renal
tubules

18

What is the formula for GFR?

M = substance filtered freely

GFR = ( UM x V ) / PM


UM = conc of M in Urine
PM = conc. of M in Plasma

V = volume of Urine per unit time

19

If a substance is ideal for GFR, what is the rate of excretion and filtration of that substance?

Mass excreted / Time = Mass filtered / Time

20

What is the formula betwen mass, volume and concentration?

Mass = volume x concentration

21

If a substance is freely filtered, what is the concentration of it in the filtrate vs in plasma?

conc in filtrate identical to the conc in plasma

22

What does the Maintenance of a normal GFR depend on?

adequate number of nephrons

Intact glomerular function

normal renal perfusion

23

Fall in GFR is associated with raised plasma levels of what?

retention of metabolic wastes

>> raised Creatinine and Urea levels in plasma

24

A decreasing GFR precedes __?

Renal failure in all forms of progressive renal disease

25

Level of GFR is a strong predictor of __?

the time to onset of renal failure

26

Name 3 substances used for GFR measurement?

Inulin
Urea
Creatinine

27

Urine collected over 10 hours = 1 Liter

Urine INULIN concentration = 300 mg/L

Concentration of INULIN in Plasma = 4 mg/L

Calculate GFR?

UV/P = GFR

Volume per hour = 1/10 = 0.1
U = 300mg/L
P = 4mg/L

300 x 0.1 / 4 = 7.5L/ hour = 125 mL/min

28

If inulin was secreted in body, what would the GFR be?

Higher than true GFR

29

Why is inulin not used clinically?

requires infusion of the polysaccharide at a continuous and constant rate for several hours

>> inconvenient and costly

30

Why is Creatinine used over inulin? Limitation?

released into the blood at a relatively constant rate

>> endogenous, no need for intravenous
infusion

31

Limitation of using creatinine for GFR?

Creatinine Clearance only gives an approximation of the true GFR

** small amount of
Creatinine is secreted by the renal tubules

** overestimate the true GFR

32

Why is very accurate GFR not required clinically?

requires blood sampling and timed urine
collections

>> error-prone due to inaccurate timing of urine collection

33

2 ways to measure GFR?

Creatinine in blood (plasma / serum) or

measurement of Creatinine Clearance (CrCl)

34

How does creatinine flow to kidneys?

not protein bound, non-polar, small size (113 D)

freely filtered and carried in blood, filtrate

35

Relationship between Plasma creatinine and GFR?

Plasma CREATININE is inversely related to GFR

36

Show how Plasma CREATININE is inversely related to GFR?

Creatinine Excretion = Creatinine Filtered (GFR x Plasma Creatinine Conc)

GFR x Plasma Creatinine = Constant

so GFR = Constant / Plasma Creatinine

37

Why creatinine not perfect for detecting changes in GFR?

Inability to detect mild to moderate reduction in GFR

GFR has to drop by 40-50% before plasma creatinine levels raise

38

What influences creatinine production?

muscle mass

Difference in Age, gender and ethnic

39

Rise in GFR by how much warrants an investigation

rise in blood Creatinine of ≥ 20% from previous levels

***even if the Creatinine level still remains within the reference interval***

40

What is Flag L and Flag H?

H = abnormally high creatinine

L = abnormally low ''

41

Why is GFR using creatinine not great for giving signs of acute kidney function deterioration?

Early acute kidney injury >> GFR reduced but not enough time for creatinine to accumulate

>> cannot reflect severity of kidney disease

42

Blood level rise causes what to rise?

Renal tubular and gastrointestinal mucosal secretion

43

trimethoprim (UTI drug), H2-blocker cimetidine can influence GFR, how?

increase the level of the
serum creatinine by decreasing creatinine secretion

44

What other biomarkers can interfere with creatinine levels?

very high level of bilirubin and acetoacetate lead to spuriously low and high creatinine results

45

Describe the relationship between GFR and serum creatinine in acute kidney disease?

GFR may fall considerably before serum creatinine is significantly increased

46

What changes in muscle mass and kidney status leads to increased plasma creatinine?

Normal muscle mass + diseased kidneys

Increased muscle mass + normal kidneys

Reduced muscle mass + diseased kidneys

47

What change in muscle mass and kidney status can mask kidney disease and poor function?

Reduced muscle mass + Diseased kidney

The serum creatinine level is low due to low muscle mass, but diseased kidney removes less creatinine >> mask disease

48

Compare a skinny vs muscular person, at the same rate of decline in GFR, the skinny person's serum creatinine level increases at higher or lower GFR than muscular?

Lower

49

Change in creatinine due to: aging?

Decrease

50

Change in creatinine due to: Female Sex

Decrease

51

Change in creatinine due to: Muscular body

Increase

52

Change in creatinine due to: Amputation

Decrease

53

Change in creatinine due to: Obesity

No change

54

Change in creatinine due to: Malnutrition, inflammation, deconditioning

Decrease

55

Change in creatinine due to: Neuromuscular diseases

Decrease

56

Change in creatinine due to: Vegetarian diet

Decrease

57

Change in creatinine due to: Ingestion of cooked meat

Increase

58

What is urea made from?

waste product of amino acid metabolism,
synthesized by the liver from ammonia and CO2

59

Urea clearance depends on what?

Urine Flow Rate

60

Movement of urea in kidneys?

Filtered freely by the glomeruli

readily diffuses back into the circulation through renal tubular membrane

61

Plasma urea Excretory load is dependent on?

protein intake

net body protein metabolism

62

Name 2 conditions that raises plasma urea levels?

Cushing syndrome, severe burn

raised urea levels due to accelerated
protein breakdown

63

How does kidney disease impact plasma urea level?

Kidney disease > decrease Renal perfusion or nephron no.

> More urea diffuse back to plasma > raise plasma urea level

64

Why is urea not good as a GFR indicator?

1. Decrease production or low protein intake >> lower plasma urea level to falsely indicate renal insufficiency

2. GFR has to drop 40% before plasma urea rises

3. Increase production or high protein intake rises plasma GFR > mask renal impairment

65

List factors that raises plasma urea levels?


* High Protein Diet
* Tissue Trauma
* Glucocorticoids
* Tetracycline
* Gastrointestinal Bleeding

66

List factors that lowers plasma urea levels?

* Liver Disease
* Malnutrition

67

What does Renal function test profile?

measurement of Creatinine and Urea conc in serum/plasma

(also Na+, K+, Cl-, HCO3-)

68

Why is RFT convenient but rather insensitive?

significant reduction of GFR but levels still within reference

Subject to various factors independent of renal function

69

Unit of Creatinine clearance?

mL/min

70

Name 1 pro and 2 cons of creatinine clearance as estimation of GFR?

Pro:
- More reliable than formula-predicted GFR

Cons:
- 24-hour urine collection is inconvenient and error-prone
- Measurement Uncertainty may be up to 30%

71

What is Cockroft and Gault formula based on?

plasma / serum Creatinine,

Age, Body Weight, Gender (diff. equations for adults and children)

72

What is good about the MDRD equations for eGFR?

more sensitive than plasma / serum Creatinine

especially in detecting mildly impaired GFR

73

GFR estimated by Cockroft and Gault formula tend to ____ GFR in advanced renal failure?

overestimate GFR in advanced renal failure

74

Cockrodt and Gault formula correlates better with measure GFR provided__?

Renal impairment is not severe and relatively stable

No inhibition of tubular secretion of creatinine by medications

Plasma [creatinine] is not within normal range

75

Difference in what Cockroft and Gault meansures vs MDRD?

MDRD = eGFR
Cockroft = creatinine clearance

76

Name 4 pros of the MDRD eGFR formula?

- No need for timed urine collection
- No need for body weight
- Adjusted for body size (to 1.73m^2 standard)
- Evaluated in subjects with varyinging renal insufficiency

77

Name 1 con of the MDRD eGFR formula?

Not validated in subjects <18 and >70 yrs, pregnant women

78

What is needed to be applied to the MDRD eGFR formula for Asians?

Asian ethnic co-efficient

79

What is the advantage of CKD-EPI over MDRD?

much less bias at
eGFR greater than 60ml/min/1.73m2

80

Name 2 benefits of CKD-EPI?

Minimising the over-diagnosis of CKD with
the MDRD equation

Lower prevalence of
CKD and better risk prediction

81

Out of all the formulas, which one is now used for eGFR?

CKD-EPI equation

82

Name of formula for eGFR in children?

Schwartz formula for estimation of GFR in Children

83

What does the Schwartz formula include as metrics?

serum Creatinine (mg/dL), child’s height (cm) and a Constant (k)

k is a constant that depends on muscle mass

84

Define CKD?

abnormalities of kidney
structure or function, present for >3 months,
with implications for health.

85

How much Albuminuria in CKD?

Albuminuria >30 mg/day

86

Why is Plasma Creatinine & Formula-predicted GFR not good for acute renal failure?

very rapid deterioration in renal function may be underestimated by the
eGFR

87

What is Goulash effect?

80% rise in creatinine after 300g of cooked beef

88

How to limit Goulash effect?

Less variability in early morning creatinine

89

How much does Strenuous exercise increase creatinine?

14%

90

Which patients are harder to measure muscle mass?

oedematous patients
Late pregnancy
severe muscle wasting
amputee
extreme body habitus

91

What diseases can highly affect plasma creatinine?

liver disease

profound hyperbilirubinaemia

92

What drugs can affect creatinine ?

Drugs inhibiting tubular creatinine secretion

(e.g., trimethoprim, cimetidine, probenecid, amiloride)

93

Factors affecting tubular secretion of creatinine?

Only one:
Drugs that induce inhibition of secretion

e.g. fenofibrate

94

Factors affecting extra-renal elimination of creatinine?

Dialysis

Drugs inhibit gut creatinase in bacteria

Increase by large volume losses of extracellular fluid

95

Main use for Cockroft & Gault formula?

Widely accepted for drug-dosing
decisions

96

Main use for Creatinine Clearance by timed urine collection?

For extremes of body composition

97

Gold standard for GFR measurement?

GFR measured by
infusion studies

98

Cystatin C is made where? Affected (or not) by what?

Cysteine protease inhibitor
Synthesized by all nucleated cells and produced at a constant
rate

Not affected by muscle mass, gender and diet

99

What increases Cystatin C by a small amount?

modest increase in production is seen in obesity,
hyperthyroidism, and inflammation

100

Renal circulation of Cystatrin C?

Freely filtered at glomerulus

Reabsorbed and metabolized by proximal tubules

only a minute amount present in urine

101

What does Cystatin C measure/ mark for?

Increases in urinary excretion= marker for PCT injury or dysfunction

102

Con of Cystatin C?

relatively high assay cost

Assay not widely available.

Decks in MBBS I CPRS Class (78):