Renal Function Tests Flashcards
5 kidney functions
- Excretion of waste products - creatinine, urea
- Maintenance of water balance
- Maintenance of blood pressure - water & sodium excretion/retention
- Maintenance of cardiac function - potassium excretion
- Maintenance of pH - excretion of hydrogen ions
2 functions of adrenal glands
- Bone function via synthesis of vit D (required for calcium absorption)
- Regulates stress response via synthesis of cortisol & adrenaline
What does the kidney filter out
- Sodium
- Chloride
- Sugar
- Amino acids
What do the kidneys reabsorb
- All glucose
- All amino acids
- Most sodium
- Chloride
What is the glomerulus responsible for
Filtering the blood
How are large mulecules kept out of nephron
Diameter of afferent arteriole much greater than diameter of efferent arteriole.
This induces a pressure within capillaries, forces molecules with a molecular weight of less than 68,000 g/mol out.
What is one of the first indicators of glomerular damage and why
- Albumin has a molecular weight of 68,000 g/mol
- The measurement of low concs of albumin in urine is one of the first indicators of glomerular damage
Glomerular function tests
Purpose of Clearance Test
Measures how effectively the kidneys filter & excrete substances from blood
Glomerular function tests
What does it mean if the clearance test is high
Higher the renal clearance, the more plasma that is cleared of the substance
Glomerular function tests
Purpose of serum creatinine test
Assesses waste product clearance
Glomerular function tests
What does it indicate if the serum creatinine is high
High in kidney dysfunction
Glomerular function tests
Purpose of serum urea test
Assesses waste product clearance
Glomerular function tests
What does it indicate if the serum urea test is high
High in kidney dysfunction
Purpose of GFR test
Estimates filtration rate of kidneys
Glomerular function tests
What does the GFR test being less than 60 suggest
Kidney disease
Glomerular function tests
Purpose of urinalysis test
Detects blood (haematuria), protein leakage (proteinuria, often albuminuria)
Glomerular function tests
What does the presence of protein/blood in the urinalysis indicate
Glomerular disease
What are the 2 commonly used clearance tests
- Creatinine clearance (CrCl) test
- Inulin clearance test
Clearance definition
The number of ml of blood cleared of a substance X per unit time, usually espressed in ml/min
Clearance test formula
(U x V) / P
- U = conc of substance in urine mmol/L
- P = conc of substance in plasma mmol/L
- V = volume of urine per unit time ml/min
Patient preparation for clearance test (5)
- Emphasise NB of accurate urine collection over 24 hours
- Avoid high protein meals - protein metabolism can influence creatinine levels
- Stop certain meds (e.g: NSAIDS) - can affect creatinine secretion
- Ensure hydration
- Maintain normal fluid intake, avoid excessive fluids - may alter kidney filtration rates
Why should the first morning urine be discarded
It contains waste accumulated overnight
Steps for24hr urine collection
- First collection in morning
- Discard
- Collect all urine for 24hrs
- Each time patient urinates it must be collected in provided container
- Kept in fridge or cool place
- Final urine sample exactly 24hrs after starting
What is needed after the 24 hr urine to calculate the clearance
Blood sample
Allows for the comparison of creatinine in blood vs urine to calculate clearance
