2 lab tests

Question 1

How can you calculate GFR?

Answer 1

GFR= (Ux)(UF)/Px

Question 2

What are 3 exogenous markers that are freely filtered?

Answer 2

• inulin
• lothalamate
• lohexol

Question 3

What are some characteristics of creatinine?

Answer 3

• produced from metabolism of muscle creatine and from dietary meat intake
• freely filtered/not reabsorbed
• small amount secreted in the proximal tubule (why calculations slightly overestimate GFR)

Question 4

What happened to the GFR if the serum creatinine quadrupled?

Answer 4

Quadrupled creatinine= GFR decrease to 1/4 its previous amount (inverse relationship)

Question 5

What are the normal values for serum creatinine in men, women, and chlidren?

Answer 5

• men= 0.9-1.3 mg/dl
• women= 0.8-1 mg/dl (women have less muscle mass)
• chlidren= 0.5-1 mg/dl
  
  • can’t estimate before 2 yo because kidneys are still developing

**blacks, men, and younger adults have more muscle mass and therefore greater creatinine production

Question 6

What factors are taken into account in the Cockcroft-Gault formula?

Answer 6

• serum creatinine
• age
• weight
• gender

**NOT race or body size (will overestimate GFR in an obese/edematous patient)

Question 7

What factors are taken into account in the MDRD formula?

Answer 7

Used by most labs to report GFR (underestimates if GFR >60 ml/min/1.73 m²) based on…

• serum creatinine
• age
• gender
• race

**NO weight adjustment!

Question 8

What factors are taken into account in the CKD-EPI formula?

Answer 8

Much more complicated equation but better at estimating GFR > 60 ml/min/17.3m², based on…

• serum creatinine
• age
• gender
• race

Question 9

What is cystatin C?

Answer 9

• protein produced by all nucleated cells
• freely filtered
• production seems less affected by age and gender than creatinine
• new estimating equations for GFR being formulated based on cystatin C

Question 10

Describe chronic kidney disease

Answer 10

• GFR < 60 ml/min/1.73 m² for > 3 months
  
  • but GFR can be normal!
• other evidence of kidney damage
  
  • proteinuria
• broken into stages I-V (V= worst, need dialysis when GFR <10 ml/min)

Question 11

Can we use equations to estimate acute kidney injury?

Answer 11

NO! Change is too fast, equations need a new steady state to be reached as creatinine rises (then it’s too late…)

**early sign can be decreased urine output

Question 12

What are the RIFLE criteria?

Answer 12

For stratifying acute kidney injury (based on creatinine and urine output criteria):

• Risk
• Injury
• Failure
• Loss of function
• End-stage renal disease

**cannot occur over more than 7 days

Question 13

What are the AKIN criteria?

Answer 13

More classification of acute kidney injury within 48 hours (based on creatinine and urine output criteria)

Question 14

What is KDIGO?

Answer 14

More defining of acute kidney injury from 2012 (still based on creatinine and urine output criteria)

Question 15

Why is creatinine not a good indicator in acute kidney injury?

Answer 15

• takes time for it to rise (typically ~48 hours from time of injury)
• even if GFR decreases to 0, creatinine typically only rises at 1-2 mg/dl/day

**biomarkers are being investigated as a better indicator (“foot prints” of actual organ damage)

Question 16

What is a normal urine protein output? What is the main identifyier of nephrotic syndrome?

Answer 16

• total urinary protein should be less than 150 mg/day
• >3.5 g/24 hours is nephrotic
  
  • low serum albumin and edema too

Question 17

Describe a urine dipstick

Answer 17

• shows a negative and positive reading or protein
• primarily detects albumin
• dependent on urine concentration
• semi-quantitative (color variation based on severity)

Question 18

What is microalbuminuria?

Answer 18

• aka moderately increased albuminuria
• defined as
  
  • 30-300 mg of albumin per 24 hours
  • 30-300 mg of albumin/g of creatinine
  • this is usually below the dipstick threshold
• most of the total urinary protein is made up of tubular protein **albumin in the urine is abnormal!

Question 19

Describe the pathophysiology of overflow, glomerular, and tubular pathology

Answer 19

• overflow
  
  • increased filtration of other proteins (normal albumin filtration)
  • normal reabsorption leads to excess “other” proteins in the urine
• glomerular (basement membrane problem)
  
  • increased filtration of albumin (normal for other proteins)
  • normal reabsorption leads to excess albumin in the urine
• tubular (kidney tubule problem)
  
  • normal filtration
  • blocked reabsorption leads to excess albumin AN “other” proteins in the urine

Question 20

Describe the normal handling of protein in the kidney. Albumin specifically?

Answer 20

• Normally small proteins and a tiny bit of albumin is filtered
  
  • albumin completely reabsorbed
  • small proteins mostly reabsorbed
• Results in a very low amount of protein in the urine
  
  • NO albumin in urine!