Kidney disease - the basics Flashcards
What are the functions of the kidney?
- Metabolic waste excretion
- Control of solutes and fluid status
- Endocrine functions
- Blood pressure control
- Acid/base balance
- Drug metabolism/excretion
What is the primary role of the kidneys?
maintain fluid and electrolyte homeostasis in response to blood pressure and hormones
How can we measure metabolic waste excretion
Measure urea and creatinine
How can we measure the control of solute and fluid status
Measure sodium and potassium
What are the endocrine functions of the kidneys?
- vitamin D
- EPO - erythropoietin
- PTH - parathyroid hormone
What are the U and Es?
- Sodium
- Potassium
- chloride
- Urea
- creatinine
- eGFR
- Sometimes bicarbonate
What are the characteristics of a substance used to measure kidney function?
- Freely filtered at the glomerulus
- Not secreted
- Not reabsorbed
What are the causes of an abnormal serum urea?
- Diet: high protein or GI bleed
- Dehydration: passive reabsorption in the proximal tubule
- Tissue breakdown e.g. corticosteroid
- Liver failure lowers urea
- Up to 40% reabsorption
What is renal clearance?
Volume of plasma which would be cleared of the substance per unit time
What is the best measure of renal clearance?
Inulin
What is the MDRD formula based on?
- Plasma creatinine concentration
- Age (adults only)
- Gender
How is the value of eGFR expressed when using the MDRD formula?
ml/min per 1.73m^2 body surface area
What is measured to calculate eGFR?
Plasma creatinine
When is it not suitable to use eGFR?
- Acute kidney injury
* When renal function is unstable
Describe stage 1 of chronic kidney disease
- eGFR >/90ml/min
* Need to have another abnormality otherwise regarded as normal
Describe stage 2 of chronic kidney disease
- eGFR 60-89ml/min
* needs to have another abnormality otherwise regarded as normal
Describe stage 3 of chronic kidney disease
- eGFR 30-59
* Moderate impairment
Describe stage 4 of chronic kidney disease
- eGFR: 15-29
* Severe impairment
Describe stage 5 of chronic kidney disease
- eGFR <15
* Advanced renal failure
What are the normal proportions of proteinuria?
- Albumin 15%
* Other proteins 85% e.g. Tamm Horsfall, immunoglobulin
What proteins does urinalysis detect?
Albumin only
What is the detection of protein in the urine dependent on?
The concentration of the urine, if it is very concentrated it will look like there is a lot more protein in the urine than there actually is so don’t depend on dipstick alone
How do you measure urinary protein excretion?
- 24 hour urine collection
- Protein:creatinine ratio (PCR) on morning spot sample
- Albumin:creatinine ration
Describe the balance of protein in proteinuria
- 70% albumin
* 30% other proteins
