Asessment of Renal Function /Acute Renal Failure Flashcards
What is the expected GFR and rate of age-related decline of GFR?
GFR (normally = 120mL/minute; 7.2L/hour)
1ml/min per year decline
How is GFR calculated?
If three criteria for markers are fulfilled, then renal clearance = GFR
Clearance = (Urinary Concentration x Volume)/ Plasma Concentration
What is the gold standard measurement of GFR?
Innulin Clearance (Freely filtered material)
(freely filtered, but just not practical as continous infusion required)
What are the markers that make a good marker for GFR calciulation?
- Marker is NOT bound to serum proteins
- Freely filtered by the glomerulus
- NOT secreted or reabsorbed by tubular cells
What are the pros and cons of Urea for measurements of GFR
- Variable (30-60%) reabsorption by tubular cells (you DON’T want any reabsorption…)
- Dependent on nutritional state, hepatic function, GI bleeding
- Very limited clinical value
When/ How is Urea produced?
Produced from Ammonia in catabolic metabolism
What limit the use of Creatinine as a measurement of GFR?
- Creatinine: GFR relationship is non-linear (worse at predicting at lower levels)
Rate of Creatining production is dependant on
* Muscularity (proportional to mass)
* Age
* Sex (higher in men)
* Ethnicity (higher in Afro-Caribbean)
What are the pros of using creatinine as a marker of GFR?
- Constantly released from muscle cells,
- freely filtered and actively secreted into the urine by tubular cells
What is the current calciulation used to get eGFR?
CKD-Epidemiology Collaboration (CDK -EPI)
* Similar/derived from MDRD
* Takes into account serum creatinine, age, sex and race (differently)
What is Cystatin C?
What is its role in Renal Function measurement?
Suggested alternative endogenout marker of renal function
- This is constitutively produced by all nucleated cells at a constant rate and is freely filtered
- Almost completely reabsorbed and catabolised by tubular cells
- NOTE: CKD NICE guidelines have included cystatin C, however, it is not used that frequently
What does urine protein:creatinine ratio measure?
- This is a quantitative assessment of the amount of proteinuria (which is a marker of renal damage)
- Measurement of creatinine corrects for urinary concentration
How can you measure Urine Protein:Creatine ratio?
Two methods to do PCR:
* 24hr urine collection (cumbersome and messy; highly inaccurate without patient education)
* Spot urine measurement
What can be investigated in a 24h urine collection?
Creatinine clearance estimation
* Stone forming elements
* Proteinuria quantification
* Electrolyte estimation
What does Leucocyte esteraste include/exclude on a urine dipstick?
negative result is significant – reliably excludes bacteria presence (positive less so)
Which Proteins are detected on a urine dipstick?
Albumin
(does not detect every protein, including not Bence-Jones Protein)
When are IV urograms performed?
Excretoion Contrast X-Ray
done more in paediatrics to look for anatomical defects)
What is the Cockroft-Gault adjustment?
Equation to estimate creatinine clearence
But
* Not the GFR directly (just creatinine)
* May overestimate low GFRs (<30mL/min)
