Measurement of renal function

Question 1

Clinical Assessment

Answer 1

Look for specific kidney functions which are affected: fluid balance, electrolyte balance, EPO production, Vitamin D3, excretion and acid/base balance

Question 2

Use of bedside clinical data

Answer 2

Weight and fluid balance charts
Degree of oedema
Dipstick testing

Question 3

Renography techniques

Answer 3

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

Question 4

Biochemical data useful for identifying renal impairment

Answer 4

Plasma/serum creatinine
Plamsa/serum urea (blood urea nitrogen)
But these usually only increase after 60% loss in renal function

Question 5

Normal range of plasma creatinine

Answer 5

40-120 umol/L

Question 6

What increases plasma creatinine

Answer 6

large muscle mass
drugs that interfere with analysis
drugs which inhibit tubular secretion
ketoacidosis
ethnicity

Question 7

What decreases plasma creatinine

Answer 7

reduced muscle mass
starvation/cachexia
immobility
pregnancy
severe liver disease

Question 8

What is blood urea nitrogen (BUN) increased by

Answer 8

high protein diet
hyper catabolic conditions
GI bleeding
muscle injury
drugs (glucocorticoids/tetracycline)
hypovolaemia

Question 9

What decreases BUN

Answer 9

malnutrition
liver disease
sickle cell anaemia
SIADH

Question 10

What is biochemical data useful for

Answer 10

Identifying renal impairment

Modifying dosages of drugs

Question 11

Definition of clearance

Answer 11

The volume of plasma completely cleared of a given substance in unit time

Question 12

What does clearance tell us about

Answer 12

Filtration
Reabsorption
Secretion
But nothing about precise tubular sites

Question 13

Equation for clearance

Answer 13

{U(x) x V}/P(x)

Question 14

Best substance for measuring GFR (and drawbacks)

Answer 14

Inulin
But - must be administered by IV to get constant plasma or serum levels
Instead creatinine is used

Question 15

Creatinine problems

Answer 15

Some is secreted at PT (over-estimation by 20%)
Colorimetry methods used - Jaffe method (under-estimation by 20%)
Venous blood and urine samples needed
Can be different with muscle diseases/damage or having eaten lots of meat - 24 hour sample is best

Question 16

eGFR

Answer 16

Different equation taking into account age, mass and plasma creatinine - and a multiplier
Called modification of diet in renal disease

Question 17

PAH to measure renal blood flow

Answer 17

Para-aminohippuric acid
Not normally present in blood
90% cleared from kidney in one passage
Some filtered, remainder secreted at PT & 10& bypasses tubule - not secreted at all

Question 18

Blood and urinary markers of early stage kidney disease

Answer 18

Kidney injury molecule 1
IL 18
Fatty acid binding proteins
Neutrophil gelatinise associated lipocalin
Cystatin C