Investigating Disorders of Renal Function

Question 1

what is renal clearance

Answer 1

theoretical concept
rate at which a substance in removed from the blood stream via the kidneys

Question 2

what is sometimes used to calculate GFR in paediatrics

Answer 2

iohexol - non-radioactive contrast agent
injected and then serial blood tests

Question 3

what endogenous substance can be used for GFR other than creatinine and what is its advanatge

Answer 3

cystatin C
no significant tubular secretion (creatinine has some)

Question 4

GFR equation

Answer 4

GFR = (concentration in urine x volume of urine x time it’s collected over)/concentration in plasma

Question 5

what type of urine sample is needed for creatinine clearance (GFR using creatinine)

Answer 5

24 hour urine collection

Question 6

when is creatinine clearance innaccurate

Answer 6

in advanced renal failure where there is very low GFR

Question 7

why is the Cockcroft-Gault equation useful

Answer 7

it is able to adjust a plasma creatinine level for age, weight and sex

Question 8

what is the Cockcroft-Gault equation

Answer 8

eGFR for men = ((140-age) x weight)/creatinine concentration x 0.81
eGFR for women = ((140-age) x weight)/(creatinine concentration x 0.85)

Question 9

what type of GFR is done most commonly in GPs

Answer 9

eGFR (only plasma creatinine measurement required) and MDRD equation

Question 10

at what GFR is MDRD equation accurate

Answer 10

in those with low GFR
not very low or normal

Question 11

what equation is better than the MDRD and why

Answer 11

EPI
it is more reliable in higher GFRs so may be able to spot kidney disease at an earlier stage

Question 12

in what populations can the MDRD and EPI equations not be applied

Answer 12

possibly very elderly
children
pregnancy
muscle mass extremes (frail, amputee, heavily built)
rapidly changing renal function
very low GFR

Question 13

what two things are used to classify CKD

Answer 13

eGFR (MDRD equation)
albumin:creatinine eqution

Question 14

definition of CKD

Answer 14

progressive and irreversible loss of kidney function caused by irreversible damage to increasing numbers of nephrons

Question 15

CKD diagnosis requires

Answer 15

eGFR<60
or eGFR >60 and one of:
- persistent proteinuria
- haematuria
- renal anatomical/genetic abnormality

Question 16

what features are associated with AKI

Answer 16

oliguria (less peeing than normal)
increases in plasma urea and creatinine (as not peeing it out)
loss in ability to regulate water, electrolyte and acid base balance

Question 17

what investigation is used to detect AKI

Answer 17

creatinine (increase from baseline)
and urine output (decrease)
(eGFR doesn’t change quickly enough to detect AKI)

Question 18

what urine output would indicate AKI

Answer 18

<0.5ml/kg/hr for >6 hours in adults
>8 hours in children

Question 19

what change in plasma creatinine indicates AKI

Answer 19

> 26 umol/l increase within 48 hours
50% increase in last 7 days

Question 20

how does the pH of urine compare to plasma

Answer 20

urine is usually significantly more acidic than plasma
urine pH < 5.5
plasma pH 7.35-7.45

Question 21

a urine pH>5.5 can be caused by

Answer 21

renal tubular acidosis type 1

Question 22

a urine Na+ of >30mmol/l suggests

Answer 22

inappropriate Na+ loss due to
- tubular damage
- inadequate ADH

Question 23

how do you measure urine concentrating ability

Answer 23

urine osmolarity

Question 24

positive leukocytes in dipstick suggests

Answer 24

UTI

Question 25

bilirubin postive
uroblinogen negative
on dipstick suggests

Answer 25

cholestatic jaundice