Chempath 18: Assessment Of Renal Function 1

Question 1

What is considered the best measure of Kidney function ?

Answer 1

GFR

Question 2

List 3 criterias that need to be fulfilled for a marker of clearance to be an accurate representation of GFR ?

Answer 2

• The marker is not bound to serum proteins
• The marker is freely filtered by the glomerulus
• The marker is not secreted or reabsorbed by tubular cells

Question 3

Name an endogenous markers that is measured clinically to estimate GFR ?

Answer 3

Creatinine

Question 4

Apart from haematuria what else can cause a +ve dipstick result for blood ?

Answer 4

Myoglobinuria

Seen in rhabdomyolysis

Question 5

What does the measure SG tell you on the urine dipstick ?

Answer 5

Specific gravity

Its a measure of urine concentration

Question 6

Which marker of multiple myeloma can be detected in the urine ?

Answer 6

Bence jones proteins

Question 7

A 50 year old, known alcoholic, presents generally unwell, seemingly intoxicated, with acute kidney injury. Urine microscopy reveals calcium oxalate Chrystals. What is the diagnosis?

Answer 7

Ethylene glycol poisoning (anti-freeze)

Question 8

List 4 different methods of imaging the renal/urological system ?

Answer 8

Ultrasound KUB
IV Urogram (paediatrics looking for anatomical defects)
CT KUB
MRI KUB

KUB = kidney ureter bladder

Question 9

Which mode of imaging is considered gold standard for identification of kidney stones ?

Answer 9

CT KUB

Question 10

Normal GFR

Answer 10

120ml/min

Age related decline of 1mL/min/year

Question 11

What is clearance

Answer 11

Can be used to measure GFR

The volume of plasma that can be completely cleared of a marker substance per unit time

Question 12

How do you calculate clearance

Answer 12

Of 3 criteria fulfilled, clearance = GFR

C = (U x V) / P
Where u = urinary concentration
V = volume
P = plasma concentration

Question 13

What is inulin

Answer 13

Marker used in research tool to measure GFR

Question 14

What are clinically viable measures of GFr

Answer 14

Single injection plasma clearance measurements using

• Cr- EDTA
• Tc - DTPA
• Iohexol

Give injection and measure urine collection using a gamma counter or take blood samples and look at the progressive reduction in radioactivity

Question 15

Give examples of exogenous markers of GFR

Answer 15

Blood urea
Serum creatinine (from muscle cells, small amount of intestinal absorption)
CDK- epidemiology collaboration
Cystatin C

Question 16

What 4 factors affect the rate of generation of creatinine

Answer 16

Muscularity
Age
Sex
Ethnicity

Question 17

What is the best way to measure GFR

Answer 17

Serum creatinine is an insensitive marker
Cystatin C is better
Constant rate infusion is a research tool
EGFR/ creatinine clearance is the best compromise in practice

Question 18

How can we measure urine protein:creatinine ratio

Answer 18

Quantitative assessment of the amount of proteinuria

Spot urine PCR correlates well with 24hr urine collection

Question 19

Types of urine examination

Answer 19

Single sampling:
Dipstick testing
Microscopic investigation
Proteinuria quantification 
Electrolyte estimation 

24 hour collection:
Creatinine clearance estimation
Stone forming elements

Question 20

What diagnosis would be suspected if a patients urine microscopy reveals calcium oxalate crystals

Answer 20

Ethylene glycol poisoning
Gets converted to oxalis acid
Precipitates with calcium in the renal tubules and ureters

Question 21

Different types of renal imaging

Answer 21

Plain KUB films 
IV urogram 
Ultrasound KUB 
CT KUB - 1st choice for kidney stones 
MRI KUB
Functional imaging - static and dynamic renograms

Question 22

name 2 equations that estimate GFR

Answer 22

overestimate - cockroft-gault
underestimate - MDRD

uses age, weight, sex, ethnicity

Question 23

why is inulin only used in research

Answer 23

requires a steady state infusion and difficult to assay