Renal Function Tests

Question 1

why are renal tests carried out?

Answer 1

to assess functional capacity, diagnose and monitor renal impairment and assess effectiveness of treatment

Question 2

what are the prerenal causes of renal impairment?

Answer 2

reduced blood flow due to blood loss or haemolysis

Question 3

what are the renal causes of renal impairment?

Answer 3

damage to renal tissue, glomerular basement membrane or tubules due to diabetic nephropathy or toxic substances

Question 4

what are the post renal causes of renal impairment?

Answer 4

obstruction due to kidney stones or prostatic cancer

Question 5

what renal tests are carried out?

Answer 5

glomerular: serum urea/creatinine, clearance and eGFR
tubular: acidification, osmolarity and urine conc

Question 6

reference range for serum urea

Answer 6

1.7 - 8.3 mmol/L

Question 7

how is serum urea analysed?

Answer 7

nitrogen content of ammonia measured

urea broken down to ammonia by enzyme urease

Question 8

what are the types of serum urea assay?

Answer 8

nesselers reaction
berthelot reaction
kinetic method

Question 9

what is the nesselers reaction?

Answer 9

nesselers reagent containing ionic salt of mercury and potassium
brown end product - spec

Question 10

what is the berthelot reaction?

Answer 10

phenol and sodium hypochlorite creates blue indophenol product - spec

Question 11

what is the kinetic method?

Answer 11

uses enzyme urease and GLDH

Question 12

what does increased urea indicate?

Answer 12

pre renal: low bp, decreased blood flow, increased protein intake
renal: renal disease, glomerular nephritis, renal failure
post renal: kidney stones, tumours, UTI

Question 13

what does decreased urea indicate?

Answer 13

pre renal: liver disease, high fluids, low protein, high protein synthesis

Question 14

what is creatine converted into in the body?

Answer 14

creatine kinase converts creatine into creatinine which is used for energy

Question 15

serum creatine reference ranges?

Answer 15

male 62-115 umol/L

female 53-97 umol/L

Question 16

what reaction is used to test serum creatinine?

Answer 16

jaffe reaction: alkaline picrate solution creates red product

Question 17

what causes a false high serum creatinine result?

Answer 17

jaffe positive substances such as pyruvic acid and hydantoin

Question 18

what is the modified Jaffe procedure?

Answer 18

absorbance is taken at two pH levels adding acetic acid

Question 19

what is the urea:creatinine ratio?

Answer 19

10:1 - 20:1

Question 20

what causes increased urea:creatinine ratio?

Answer 20

prerenal azotemia (low blood delivery)
decrease muscle mass
GIT bleeding, fever, burns

Question 21

what causes decreased urea:creatinine ratio?

Answer 21

low protein intake, severe liver disease

Question 22

what are the glomerular function tests?

Answer 22

clearance test and estimated GFR

Question 23

what is the clearance test equation?

Answer 23

C = (U x V) /P

Question 24

What are the eGFR equations?

Answer 24

cockcroft-gault and MDRD