AKU CHS Department of Anaesthesiology

Renal function tests

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 Renal function tests

 Renal function tests are a group of laboratory tests that assess the health and function of
the kidneys.
 These tests help in diagnosing kidney diseases, monitoring kidney function in patients
with existing conditions, and evaluating the effectiveness of treatments.
 Here are the key parameters commonly included in renal function tests, along with their
details:
 Urinalysis (U/A)
 A simple, inexpensive screening test
 How effectively the kidneys are clearing circulating substances .
 Physically
 For things like color, odor, appearance, and concentration (specific gravity)
 Specific gravity: shows urine concentrating ability of the kidney. Normal = 1.003-1.030

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 Chemically
 For substances such as protein, glucose, and pH (acidity/alkalinity);
 Microscopically
 For the presence of cellular elements (red blood cells, white blood cells, and
epithelial cells), bacteria, crystals, and casts (structures formed by the deposit of
protein, cells, and other substances in the kidneys' tubules)
 Proteinuria
 Healthy kidneys filter all proteins from the bloodstream and then reabsorb
them, allowing no protein, or only slight amounts of protein, into the urine

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 The persistent presence of significant amounts of protein in the urine is an
important indicator of sever glomerular/kidney disease
 Microalbuminuria - diabetic nephropathy
- Normal 6-8mg/dl
- 24-hour urine collection should contain no more than 150 mg of protein)
 Filtration is the most clinically assessed renal function.
 GFR normal value = 90-140 ml/min.
 After age of 30, 10% decline in GFR per decade.
 15ml/min require dialysis.
 How can you calculate GFR?
 Cockroft - Gault eGFR (mL/min) =(140 - age) × weight (kg)/ (Cr × 72) (× 0.85 for
female patients)

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 Serum creatinine

 Creatinine - a waste product of muscle energy metabolism, produced at a constant

rate that is proportional to the muscle mass of the individual
 Is filtered from the blood by the kidneys and excreted into the urine.
 The test measures blood levels of creatinine.
 Production of creatinine depends on an individual's muscle mass, which usually
fluctuates very little.
 Normal value = ???
 What does it mean low creatinine?
 Inversely proportional to GFR
 Doubling creatinine concentration shows 50% reduction in GFR
 Normal 0.6-1.2mg/dl for male and 0.5-1.1 for females

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 Creatinine clearance

 This test evaluates how efficiently the kidneys clear a substance called creatinine
from the blood
 Because the body does not recycle it, all of the creatinine filtered by the kidneys in
a given amount of time is excreted in the urine
Making creatinine clearance a very specific measurement of kidney function
 Has direct reflection of GFR.
 Best estimation of renal reserve.
 Normal 90-140ml/min
– 50- 80ml/min- mild renal dysfunction
– <10ml/min- anepheric (absence of kidney)

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 Blood Urea Nitrogen

 Urea is a by-product of protein metabolism.

 This waste product is formed in the liver, then filtered from the blood and
excreted in the urine by the kidneys.
 Insensitive measurement of GFR
 Increased by - protein intake
– Dehydration
– GI bleeding

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 Normal 5 - 25mg/dl
– > 50mg/dl almost always reflect decreased GFR
 With normal kidney function the amount of creatinine in the blood remains
relatively constant and normal.
 Because creatinine is affected very little by liver function, an elevated blood
creatinine is a more sensitive indication of impaired kidney function than the BUN

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 Urine output(U/O)
 is an important measure of renal function and can provide valuable information about kidney health
and overall fluid balance in the body.
 The following are key aspects related to measuring urine output in the context of renal function:
 Total Daily Urine Output
 Definition: This is the total volume of urine produced in a 24-hour period.
 Normal Range: Typically, normal urine output is about 800 to 2000 mL per day for adults, depending
on fluid intake, hydration status, and other factors.
 Significance:
 Oliguria: Urine output less than 400 mL per day may indicate acute kidney injury (AKI) or severe
dehydration.
 Anuria: Urine output less than 50 mL per day is considered anuria and may indicate severe kidney
failure.
 Polyuria: Excessive urine output (greater than 2000 mL per day) can be seen in conditions such as
diabetes mellitus or diabetes insipidus.

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