MBBS Program
Laboratory Medicine and Diagnostic Radiology
Med 423
Renal diseases and renal
function tests
No voice note
( ipped class)
Student learning outcomes
At the end of this lecture the students will be able to :
1. Identify the anatomy and working unit of the kidney.
2. List normal kidney function
3. Describe the types of lesions detected by the renal function tests.
4. List the clinical applications and indications of renal function tests.
5. Outline renal function tests.
6. Interpret the results of renal function tests.
Contents
1. Kidneys, Kidneys Functions and Common diseases of the kidney
2. Renal function tests:
A-Urine analysis
B-Blood examination
Kidneys
Each kidney weighs about 150 g in adult human.
Their collective weight about 0.4% of total body weight.
The kidneys have a rich blood supply and normally receive
about 25% of the cardiac input.
The functional renal unit is the nephron
Parts of the nephron
Kidneys Functions
1- Waste excretion:
Formation and excretion of urine and the waste products of protein metabolism
The main steps of urine formation are :
1-Glomerular filtration
2-Tubular reabsorption
3-Tubular secretion
2- Homeostatic function:
Maintenance of ECF volume and composition (acid-base balance and electrolyte balance)
3- Endocrine Function: Hormones synthesis.
4- Metabolic Function:
Perform gluconeogenesis supply glucose during starvation
Common diseases of the kidney
1. Acute renal failure: a sudden loss of renal function.
Causes:
Pre renal: hypotension & blood loss
Renal: infection, toxins & drugs
Post renal: UT obstruction by stone or tumor
2. Chronic renal failure: It is a gradual loss of renal functions
Causes: caused by a long-term illness like
Diabetes mellitus (43%)
Hypertension (26%)
Inflammatory, immunological, or hereditary diseases
May follow acute failure
3. Kidney stones
Definition: it is a crystalline mass in urinary tract Severe pain & may obstruct the
tract.
Prevalence: Affects 12% of men & 5% of women
Types:
1) Calcium oxalate stones 60-80%
intake of Na, protein & oxalate
2) Uric acid stones 10 %
Seen with acidic PH urine & Gout
3) Infection stones (Struvite) 5-7 %
Associated with UTI Common in female
4) Cystine stones 1-3 %
Genetic cystine in urine
Begins at Young age CRF
4. Hematuria: blood loss in the urine.
5. Proteinuria: the loss of protein especially albumin in the
urine.
6.Microalbuminuria: slight increase in urinary albumin
excretion.
7.Electrolyte disorders (acid/base imbalance)
8. Nephrosis: degeneration of renal tubular epithelium.
9.Nephritis: inflammation of the kidneys Chronic or recurrent
urinary tract infections
10. Hypertension: that has failed to respond to multiple forms of
anti-hypertensive medication or could have a secondary cause.
Renal Function Tests
They are broad range of tests that investigate the normal functions
performed by the kidney.
RFTs together with careful history, physical examination and
imaging, can contribute to making an accurate diagnosis of
specific kidney disease
Clinical applications of renal function tests
why to teste the renal function?
1. To asses the functional capacity of kidney
2. Screening & Diagnosis of kidney disease.
3. Follow up the progression of kidney disease
4. Monitor the response to treatment
5. As a routine preoperative investigation.
6. As a routine precaution after starting certain drugs to check if kidney is damaged
(as a side-effect).
When to assess renal function?
kidney function tests are used in assessment of:
1) Kidney disorders:
Family history of Chronic renal disease
Urinary tract infections (UTI)
Renal stones
Obstruction to the lower UT
2) Vulnerable groups:
Old age
Low birth weight
3) Systemic diseases:
DM, Hypertension
Autoimmune disease, Systemic infections
4) Drug toxicity
5) Preoperative
Renal function tests:
Renal function tests are divided into the following
A-Urine analysis
B-Blood examination
C-Glomerular Function Test
D-Tubular Function Test
A) Urine Analysis
Urine examination is an extremely valuable and most easily
performed test for the evaluation of renal functions.
It includes:
1 - Macroscopic (physical) examination,
2 -Microscopic examination of sediments.
3- Chemical examination
1) Macroscopic (physical) examination
Color:
Dark yellow, orange: (concentrated).
Greenish yellow: (bile).
Reddish: (blood).
Odour:
Normal: Faint aromatic
Specific (characteristic): (protein blood bile).
Acetone odour: DM
Aspect:
Clear: (Normal-glucose- acetone).
Turbid: (blood- protein- pus -bile).
Reaction to L.P:
Alkaline PH: UTI
Volume: (24 hour urine sample)
Normal: 1- 2.5 Litre/day
Polyuria: -Urine Output > 2.5 DM & DI
Oliguria: -Urine Output < 500 AGN & Renal Failure
Anuria:- Urine output < 100 Renal Failure (obstruction)
Specific gravity: by urine strips.
Normal: 1.005 to 1.030
Increased: dehydration, DM & albuminuria
Decreased: increased fluid intake, renal tubular damage
2) Microscopic examination
The presence of the following may indicates renal disease:
RBCs: >2
WBCs, Pus cells: >5/HPF (pyuria
Crystals: urate
Casts: (RBCs or WBCs stick together)
3) chemical examination
By urine strips to detect:
Protein, Glucose, Ketone bodies, RBCs, Nitrites, Bilirubin and others
Types of Urine analysis:
1)Routine urine analysis
2) 24 hours urine analysis:
Simple diagnostic procedure that measures the components of
urine.
Cheap, sensitive and is used to assess kidney function, hormones
other substances.
24 hour urine collection is a safe, noninvasive procedure that is
usually done without direct assistance.
Factors interfere with the accuracy of a 24 hour urine collection:
1- Forgetting to collect some of urine
2- Going beyond 24 hour collection period and collecting excess urine
3- Losing urine from specimen container through spilling
4-Not keeping urine cold during collection period
24 hour urine analysis needed for creatinine clearance
B) Blood examination
Done to measure substance in blood that are normally excreted by
kidney.
Their level in blood increases in renal dysfunction.
Blood markers of renal functions: routine analysis
1- creatinine
2- urea
3- uric acid
4- electrolyte
1) Urea = The blood urea nitrogen (BUN)
It is a nontoxic end product of protein breakdown.
Normal range: 8-25 mg/dL (2.5-7.1 mmol/L)
Variation of blood urea: 1- Azotemia
2- Low blood urea
Azotemia : = Increased BUN
A) Increased protein catabolism:
1- Increased dietary protein
2- Severe stress: MI, fever, etc
B) Impaired renal function
1- Pre renal azotemia:
Shock & renal hypoperfusion
2- Renal azotemia:
acute tubular necrosis
3- Post renal azotemia:
obstruction of urinary flow
2) Plasma Creatinine
Breakdown product of Creatine-p in muscle tissue.
Released from skeletal muscle at a steady rate.
The kidneys usually completely filter creatinine from the blood.
A high level of creatinine suggests a renal problem.
Plasma creatinine is inversely related to glomerular filtration rate (GFR).
The normal range of plasma creatinine:
Male: 0.8 1.3 mg/dl.
Female: 0.6 1 mg/dl.
Alteration of plasma creatinine level
1) Increased plasma creatinine
1) Impaired renal function
2) Very high protein diet
3) Anabolic steroid users why
4) Vary large muscle mass body builders, giants, acromegaly patients
2) Decreased plasma creatinine:
1)Pregnancy.
2)Low-protein Diet.
3)Decreased muscle mass.
4)Liver disease.
Urea Vs Creatinine
Urea:
More sensitive than Creatinine (rises earlier and more rapidly).
Less reliable indicator of glomerular function than creatinine
Creatinine:
More specific than serum urea (not affected by non renal factors like urea)
Most reliable simple biochemical test of glomerular function.
3) serum uric acid
It is the major product of Purines catabolism.
Purines are derived from :
1- catabolism of dietary nucleic acid
2- degradation of endogenous nucleic acids.
Reference range:
Male: 3.5 - 7 mg/dl
Female: 2.5 - 6 mg/dl
In humans :75% of uric acid excreted in urine & 25% into GIT
Hyperuricemia: may be:
Metabolic: increased synthesis of uric acid.
Renal: decreased renal excretion of uric acid
C) Glomerular function test:
(Glomerular filtration rate (GFR)
GFR is measured by using the clearance of a substance
present in plasma that is filtered freely at the glomerulus, but
is neither reabsorbed nor secreted by the tubules.
The GFR is the best measure of glomerular function.
GFR number tells how much kidney function is.
severity of renal disease GFR (inverse proportion)
Inulin clearance and creatinine clearance are used to measure the GFR.
Interpretation of GFR
Normal 125 mL/min.
Decreased Renal reserve: 60-100. ml/min
Mild Renal impairment: 40-60 ml/min
Moderate insufficiency: 25-40. ml/min
Renal failure: <25. ml/min
ESRD: <10. ml/min
Send Stay
Creatinine Clearance:
It compares the concentration of creatinine in urine with its
concentration in the blood.
Useful in the diagnosis and prognosis of the kidney disease.
Performed by obtaining:
24-hours urine specimen
blood specimen within the period of urine collection.
Calculation of creatinine clearance =
CCr = Creatinine Clearance
Ucr = Urine Creatinine
PCr = Plasma Creatinine
The value of creatinine clearance:
reflects the body's ability to excrete creatinine.
Normal range :
Male: 97 -137 ml/min.
Female: 88 -128 ml/min
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Decreased creatinine clearance ( ed GFR).
1-Impaired kidney function.
2- Dehydration.
3- Heart failure.
4- Hemorrhage.
Increased creatinine clearance (hyper filtration)
1- During pregnancy.
2- High protein diet.
D) Tubular function tests
1) Urine Concentration Test:
The ability of the kidney to concentrate urine is a test of
tubular function.
Needs water deprivation for 14 hrs in healthy individuals.
Not be performed on a dehydrated patient.
Interpretation of Urine Concentration Test:
Normal: if specific gravity of > 1.02 .
Non function kidney: Specific gravity of 1.008 to 1.010.
( isotonic with plasma)
Sconcentrated test
durine urine
pseedetioncapacity
2) Urine Dilution (Water Load) Test
After an overnight fast the subject empties his bladder
completely and is given 1000 ml of water to drink.
Urine specimens are collected for the next 4 hours, the
patient emptying bladder completely on each occasion.
Normal:
at least 700 ml urine is excreted in 4 hrs.&
t
at least one specimen will have a specific gravity less
than 1.004.
Severely damaged Kidney: can not excrete:
urine with specific gravity lower than 1.010 or
volume above 400 ml in this time.
Not be done if there is edema or renal failure;
we
(water intoxication may result)
Take Home Messages
Renal Function Tests (RFTs) are broad range of tests that investigate the
normal functions performed by the kidney.
Urine analysis includes: macroscopic, microscopic and chemical examination.
Blood markers of renal functions (routine analysis) include:
1) creatinine
2) urea
3) uric acid
4) Electrolyte
Take Home Messages
Urea is more sensitive than Creatinine (rises earlier and more rapidly).
Creatinine is the most reliable simple biochemical test of glomerular function
The GFR is the best measure of glomerular function.
Inulin clearance and creatinine clearance are used to measure the GFR.
creatinine clearance compares the concentration of creatinine in urine with
its concentration in the blood.
Normal creatinine clearance : Male: 97 -137 ml/min & Female: 88 -128
ml/min
Clinical Chemistry: Principles,Techniques, and Correlations (7th edition, 2013 ) Michael L.
Bishop MS MT , Edward P. Fody MD , Larry E. Schoeff. By Lippencott williams & Wilkins
Clinical Biochemistry Lecture Notes, (9th edition 2013) By Walker S etal, by Wiley
Blackwell
Tietz Fundamentals of Clinical Chemistry and molecular biology ( 7th Edition, 2015),
Burtis CA and Bruns DE , by Slsevier
Electronic Materials:
1) Saudi Digital library https://sdl.edu.sa/SDLPortal/ar/Publishers.aspx
2)EBSCO :http://search.ebscohost.com
3) https://www.uabmedicine.org/-/kidney-stones-a-marker-of-overall-kidney-
health
