Lecture 6: Clinical renal failure and tests Flashcards
Essentially what is renal failure?
- reduction in GFR (note can be chronic or acute)
What are the blood tests for renal function?
- Creatinine
- Urea
What are the features of plasma urea?
- Excretory product from waste nitrogen
- Formed in liver from A.As
- 35g per day formed on average, ammount depends on:
- Protein intake
- Protein breakdown
- Bleeding into GIT (equivalent to increrased protein diet as increased protein in GI tract)
How is urea handled in the kidneys?
- freely flitered
- There is some “back diffusion” throughout nephron
- This fraction increases when flow rate is slow (i.e dehyrdation)
- Excretion dependant on GFR but relationship NOT exact
Which test is a better test for renal function, creatinine or urea and why?
- Creatinine as urea rises more in dehyrdration
What are the features of creatinine?
- Derived from creatine in muscle
- No biological function - purely waste
- About 1% of muscle creatine converts into creatinine spontaneously everyday
- Production proportional to muscle mass
- Freely filtered in kidneys and NO tubular reabsorption, hence:
- creatinine clearance rate is proportional to GFR
- Plasma creatinine conc. rises as GFR falls
- creatinine clearance rate is proportional to GFR
How can creatinine levels be artificially changed?
- Large meat or fish intake
- this will result in a falsely lower eGFR
What are the used in eGFR?
- Weight (doesn’t take into account muscle mass)
- Gender (females have lower muscle mass)
- Age (older people have reduced muscle mass)
What are the limitations of eGFR?
- If muscle mass is unusually high or low
- It is only valid for patients in steady-state
- It is not valid if creatinine is rising (acute renal failure) or fallling (recovering from acute kidney injury)
What are the features of acute kidney injury?
- Sudden rapid reduction in GFR
- Happens over days/weeks
- Usually reversible
- Aetiology
- Pre-renal
- Renal
- Post-renal
What are the causes of pre renal AKI?
- Decreased blood flow
- Dehydration
- Septic shock
- Haemorrhage
- Cardiogenic shock
- Severe renal artery stenosis
- Decreased BP
- dehydration
- Infection
- Heart failure
- Surgery
How do we diagnose pre-renal AKI?
- History: reasons for low BP: hydration, bleeding, infection, chest pain 2. Check urine output: often oliguric <1L/day 3. Blood test: creatinine, high K+, high phosphate, low Ca2+
Treatment for pre-renal AKI. Outcomes??
- Fix the underlying problem: eg; rehydrate, treat bleed, fix heart, ABs etc
- Outcomes:
- Patient gets better
- Acute Tubular Necrosis (renal)
Renal AKI
80% Acute Tubular Necrosis: -Mainly due to pre-renal (also drugs and toxins) -Oliguria and renal failure even after underlying cause is fixed -4-6wk recovery Glomerulinephritis
ATN blood tests will show
-High creatinine -Low urine output (oliguria) -High Potassium
Stages of Chronic Kidney Disease and the consequences associated
..
Patient Symptoms(feelings)/signs of CKD
Nothing till later stages.
Then ureamai and hypertensive
maybe also oedema, raised JVP
