Lab 3 Renal Investigations Flashcards
What are the main analytes measured in biochemical kidney function tests?
Serum creatinine, urea, and uric acid
These analytes are primarily excreted through urine.
What is the purpose of clearance tests in kidney function assessment?
To evaluate the glomerular filtration rate (GFR) = volume of blood filtered by the kidneys per minute.
Clearance tests measure how well the kidneys can filter substances from the blood.
What is creatinine produced from?
Muscle metabolism (creatine breakdown)
True or False: Creatinine is considered a sensitive marker of renal function.
False
What factors can cause variability in serum creatinine levels?
- Muscle mass
- Diet
- Age
- Activity level
What is urea produced from?
Protein nitrogen metabolism
Liver converts ammonia to urea
What are the causes of increased serum urea?
- Pre-renal causes (reduced blood flow to kidneys)
- dehydration,
- high protein intake,
- high muscle breakdown. - Renal Causes (kidney disease)
- Acute kidney injury
- chronic kidney disease - Post renal causes (obstruction of urine flow)
- Kidney stones
- Severe UTI - Others
- GI bleeding
- Severe burns/trauma
What is the Glomerular Filtration Rate (GFR)?
estimates volume of blood filtered by the kidneys per minute
- estimates how efficient glomeruli are at filtering blood.
What are the types of kidney function tests?
- Glomerular function tests
- Tubular function tests
- Blood tests
- Urinalysis
What criteria must a substance meet to accurately measure GFR?
- Freely filtered by the glomerulus
- Neither reabsorbed nor secreted by the tubules
- Not metabolised by the kidney
- Produced constantly by the body
- Ideally endogenously produced
What is considered the gold standard for measuring GFR?
Inulin
List the limitations of estimated GFR (eGFR).
- Influenced by muscle mass
- Influenced by diet
- Influenced by age
- Population differences (children, elderly, dialysis patients)
- Rapid changes in acute kidney injury
- Severe liver disease affecting creatinine production
- Changes during pregnancy
- Drug effects on creatinine excretion
What is glycosuria?
Presence of glucose in the urine
What are the common causes of glycosuria?
- Hyperglycaemia (diabetes)
- Benign conditions (pregnancy, stress, exercise)
- Pathological conditions (renal tubular defects)
What is proteinuria?
Presence of protein in the urine
What is the normal excretion limit for protein in urine?
<150mg/day
How to measure proteinuria?
- Urine dipstick (detects mainly albumin)
- 24hr urine protein collection (measures total protein excretion over 24hrs)
What can proteinuria in pregnancy indicate?
Pre-eclampsia
What are initial presentations of renal disease?
- Dysuria
- Polyuria
- Nocturia
- Renal pain
- Ureteric colic
Define Chronic Kidney Disease (CKD).
Progressive loss of kidney function over time, usually irreversible
What does high serum creatinine levels indicate?
Reduced kidney function
- chronic kidney disease
- acute kidney injury
What does high serum urea (BUN) levels indicate?
Dehydration, high protein intake, kidney dysfunction.
What helps to differentiate between pre-renal, renal, and post-renal causes of BUN/Creatine abnormalities
BUN:Creatinine ratio
What is urinary protein concentration used for?
Measuring kidney function
Detecting proteinuria
Causes of proteinuria
- Glomerular damage = increased permeability causing proteins to leak into urine
- Tubular dysfunction = impaired reabsorption of smaller proteins
- Overflow proteinuria = excess proteins excess renal processing capacity
What causes severe proteinuria?
Nephrotic syndrome
How is eGFR calculated?
Using serum creatinine levels
What does low eGFR indicate?
Decreased kidney function
- Indicates chronic kidney disease if present for >3months
What further tests should be performed if eGFR is low
Serum creatinine + urea - to confirm renal function decline
Urinalysis = check for proteinuria
kidney ultrasound = detect obstruction
What does a sudden drop in eGFR indicate?
Acute kidney injury
Caused by dehydration, infection, drugs (NSAIDs), urinary obstruction
What does normal eGFR but abnormal urinalysis indicate?
Early kidney damage
- look for proteinuria
