2 lab tests Flashcards
How can you calculate GFR?
GFR= (Ux)(UF)/Px
What are 3 exogenous markers that are freely filtered?
- inulin
- lothalamate
- lohexol
What are some characteristics of creatinine?
- 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)
What happened to the GFR if the serum creatinine quadrupled?
Quadrupled creatinine= GFR decrease to 1/4 its previous amount (inverse relationship)
What are the normal values for serum creatinine in men, women, and chlidren?
- 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
What factors are taken into account in the Cockcroft-Gault formula?
- serum creatinine
- age
- weight
- gender
**NOT race or body size (will overestimate GFR in an obese/edematous patient)
What factors are taken into account in the MDRD formula?
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!
What factors are taken into account in the CKD-EPI formula?
Much more complicated equation but better at estimating GFR > 60 ml/min/17.3m2, based on…
- serum creatinine
- age
- gender
- race
What is cystatin C?
- 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
Describe chronic kidney disease
- 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)
Can we use equations to estimate acute kidney injury?
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
What are the RIFLE criteria?
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
What are the AKIN criteria?
More classification of acute kidney injury within 48 hours (based on creatinine and urine output criteria)
What is KDIGO?
More defining of acute kidney injury from 2012 (still based on creatinine and urine output criteria)
Why is creatinine not a good indicator in acute kidney injury?
- 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)
What is a normal urine protein output? What is the main identifyier of nephrotic syndrome?
- total urinary protein should be less than 150 mg/day
- >3.5 g/24 hours is nephrotic
- low serum albumin and edema too
Describe a urine dipstick
- shows a negative and positive reading or protein
- primarily detects albumin
- dependent on urine concentration
- semi-quantitative (color variation based on severity)
What is microalbuminuria?
- 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!
Describe the pathophysiology of overflow, glomerular, and tubular pathology
- 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
Describe the normal handling of protein in the kidney. Albumin specifically?
- 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!
