Lab test for renal failure

Question 1

Describe biochemical features of glomerular disease

Answer 1

Decrease in filtration, causing reduced urine volume, increased plasma creatinine/urea, hyperkalaemia, hyperphosphataemia, and/or metabolic acidosis

Protein- and haematuria

Question 2

Describe biochemical features of tubular disease

Answer 2

Result in reduced resoprtion, presenting as polyuria, metabolic acidosis, proteinuria (small proteins) and glycosuria

Question 3

State the assessments for glomerular function.

Answer 3

Analysis of proteinuria, microalibuminuria, or ACR

Question 4

What does microalbuminuria tell us?

Answer 4

Risk of developing a CVD. Using a 24hr urine sample

Question 5

Match the following: ACR

1. > 3mg/mmol
2. > 70mg/mmol
3. > 30mg/mmol

A. Clinically significant
B. Nephrotic syndrome
C. Glomerular damage
.

Answer 5

1A
2C
3B

Question 6

ACR is used for….

Answer 6

Staging CKD

Screen diabetic patients using random urine samples

Question 7

What are 3 types of proteinuria

Answer 7

Overflow (Bence jones proteins)
Tubular (Low Mw)
Glomerular (high Mw)

Question 8

What is an ideal marker of GFR?

Answer 8

1) freely filtered at the glomerulus, 2) not secreted or reabsorbed by renal tubular cells, 3) easy and cheap to measure

Question 9

State some exogenous markers of GFR

Answer 9

Inulin(gold standard), 51Cr-EDTA (clinical standard, but expensive and hard to measure), 99mTc-DTPA (difficult to measure) and P-aminohippuric acid (renal plasma flow determination)

Question 10

State some endogenous markers of GFR

Answer 10

Urea - underestimates GFR (because some is reabsorbed)
Creatinine - overestimates GFR depeding on muscle mass, ethnicity, age, sex
CystatinC - most accurate but expensive

Question 11

Compare eGFRcreatinine vs eGFRcystatin C

Answer 11

Creatinine

• less accurate as it is affected by more things and not validated in many groups
• Affected by diet
• Cheap

CystatinC

• Expensive but accurate
• Overestimates GFR in hypothyroid, and underestimates GFR in hyperthyroid.

Question 12

What are some tests for tubular function?

Answer 12

• Ability to excrete/retain water
• Ability to maintain acid base balance
• Ability to reabsorb small proteins, glucose and amino acids

Question 13

Ability to excrete/retain water test

Answer 13

Determines kidneys ability to concentrate urine. Tested using urine sodium osmolality and volume, serum sodium & osmolality or fluid deprivation test.

Question 14

Ability to maintain an acid-base balance test

Answer 14

Urine/blood pH, anion gap or serum bicarbonate

Question 15

Ability to maintain electrolyte balance test

Answer 15

Serum sodium & potassium or random urine sodium and potassium to calculate the fractional excretion

Question 16

Ability to reabsorb small proteins, amino acids and glucose test

Answer 16

Used to determine tubular function. Tubular proteinuria can be measured by analysing low molecular weight proteins in urine (microglobins). Whereas serum and urine aminoacids are used to determine the presence of aminoaciduria.