1. TESTS TO MEASURE KIDNEY FUNCTION, DAMAGE AND DETECT ABNORMALITIES
Dr. Parin Hedayati

2. An Introduction to the Urinary System
Produces urine
Transports urine towards bladder
Temporarily store urine
Conducts urine to exterior

3. Healthy kidneys remove wastes and excess fluid from the blood.
Blood and urine tests show how well the kidneys are doing their job.
Urine tests can show how quickly body wastes are being removed and whether the kidneys are leaking abnormal amounts of protein.

4. The Function of Urinary System
Excretion & Elimination:
removal of organic wastes products from body fluids (urea, creatinine, uric acid)
Homeostatic regulation:
Water -Salt Balance
Acid - base Balance
Enocrine function:
Hormones B) C)

5. Kidney – basic data Urine excreted daily in adults:about 1.5L
Kidneys only recieve 1% of total body weight
The renal blood flow= 20% of cardiac output
Plasma renal flow= PRF about 600 mL/Min./1.73 M2
Reflects two processes
Ultrafiltration (GFR): 180 L/day
Reabsorption: >99% of the amount filtered

6. Kidney Function
A plumbers view

7. How do you know it’s broken?
Decreased urine production
Clinical symptoms
Tests

8. Where can it break? Pre-renal Renal (intrarenal)
Post-renal (obstruction)

9. Causes of kidney functional disorders
Pre-renal e.g. decreased intravascular volum
Renal e.g. acute tubular necrosis
Postrenal e.g. ureteral obstruction
Oliguria is a significant finding in a patient. An example is provided by Case 3 in the Chem Path tutorials. The traditional classification of causes is into prerenal, renal and postrenal. Usually the cause of the oliguria is obvious and can be appropriately managed.

10. Why Test Renal Function?
To identify renal dysfunction.
To diagnose renal disease.
To monitor disease progress.
To monitor response to treatment.

11. When should you assess renal function?
Older age
Family history of CKD
Decreased renal mass
Low birth weight
Diabetes Mellitus (DM)
Hypertension (HTN)
Autoimmune disease
Systemic infections
Urinary tract infections (UTI)
Nephrolithiasis
Obstruction to the lower urinary tract
Drug toxicity
Nephrolithiasis: The process of forming a kidney stone, a stone in the kidney

12. Biochemical Tests of Renal Function
Measurement of GFR
Clearance tests
Plasma creatinine
Renal tubular function tests
Osmolality measurements
Specific proteinurea
Glycouria
Aminoaciduria
Urinalysis
Appearance
Specific gravity and osmolality pH
osmolality
Glucose
Protein
Urinary sediments

13. Biochemical Tests of Renal Function
Measurement of GFR
Clearance tests
Plasma creatinine

14. Measurement of glomerular filtration rate
GFR can be estimated by measuring the urinary excretion of a substance that is completely filtered from the blood by the glomeruli and it is not secreted, reabsorbed or metabolized by the renal tubules.
Clearance is defined as the (hypothetical) quantity of blood or plasma completely cleared of a substance per unit of time.
Inulin

15. Biochemical Tests of Renal Function
Measurement of GFR
Clearance tests
Plasma creatinine
Urea, uric acid and β2-microglobulin

16. The normal value for GFR is 90 or above.
A GFR below 60 is a sign that the kidneys are not working properly.
A GFR below 15 indicates that a treatment for kidney failure, such as dialysis or a kidney transplant, will be needed.

17. Creatinine
1 to 2% of muscle creatine spontaneously converts to creatinine daily and released into body fluids at a constant rate.
Endogenous creatinine produced is proportional to muscle mass, it is a function of total muscle mass the production varies with age and sex
Dietary fluctuations of creatinine intake cause only minor variation in daily creatinine excretion of the same person.
Creatinine released into body fluids at a constant rate and its plasma levels maintained within narrow limits  Creatinine clearance may be measured as an indicator of GFR.

18. Creatinine clearance and clinical utility
The most frequently used clearance test is based on the measurement of creatinine.
Small quantity of creatinine is reabsorbed by the tubules and other quantities are actively secreted by the renal tubules  So creatinine clearance is approximately 7% greater than inulin clearance.
The difference is not significant when GFR is normal but when the GFR is low (less 10 ml/min), tubular secretion makes the major contribution to creatinine excretion and the creatinine clearance significantly overestimates the GFR.

19. Creatinine clearance clinical utility
An estimate of the GFR can be calculated from the creatinine content of a 24-hour urine collection, and the plasma concentration within this period.
Creatinine clearance in adults is normally about of 120 ml/min,
The accurate measurement of creatinine clearance is difficult, especially in outpatients, since it is necessary to obtain a complete and accurately timed sample of urine

20. Use of Formulae to Predict Clearance
Formulae have been derived to predict Creatinine Clearance from Plasma creatinine.
Plasma creatinine derived from muscle mass which is related to body mass, age, sex.
Cockcroft & Gault Formula
CC =K [(140-Age) x weight(Kg))] / serum Creatinine (mg/dL)
k = 1 for males & 0.85 for females

21. Plasma Urea
Urea is the major nitrogen-containing metabolic product of protein catabolism in humans,
Its elimination in the urine represents the major route for nitrogen excretion.
More than 90% of urea is excreted through the kidneys, with losses through the GIT and skin
Urea is filtered freely by the glomeruli
Urea production is increased by a high protein intake and it is decreased in patients with a low protein intake or in patients with liver disease.

22. Plasma Urea
Many renal diseases with various glomerular, tubular, interstitial or vascular damage can cause an increase in plasma urea concentration.
The reference interval for serum BUN of healthy adults is 5-39 mg/dl. Plasma concentrations also tend to be slightly higher in males than females. High protein diet causes significant increases in plasma urea concentrations and urinary excretion.

23. Measurement of plasma creatinine provides a more accurate assessment than urea because there are many factors that affect urea level.
Nonrenal factors can affect the urea level (normal adults is level 5-39 mg/dl) like:
Mild dehydration,
high protein diet,
increased protein catabolism, muscle wasting as in starvation,
reabsorption of blood proteins after a GIT haemorrhage,
treatment with cortisol or its synthetic analogous

24. Urinalysis Appearance - blood, colour, turbidity.
Specific gravity - sticks measure ionic particles only, not glucose.
pH - normally acidic, except after a meal.
Glucose - the presence of glucose in urine may indicate increased blood glucose, or tubular disorder.
Proteinuria - the presence of protein in the urine may be caused by glomerular leak, raised serum low-molecular weight proteins, Bence Jones' proteins, myoglobulin, or protein of renal origin.
Microscopy - urinary tract infection will show polymorphs with no casts; acute glomerulonephritis will show cells and casts; chronic glomerulonephritis shows little sediment.

25. Imaging Tests Ultrasound
This test uses sound waves to get a picture of the kidney. It may be used to look for abnormalities in size or position of the kidneys or for obstructions such as stones or tumors.

26. CT Scan
This imaging technique uses contrast dye to picture the kidneys. It may also be used to look for structural abnormalities and the presence of obstructions.

27. kidney Biopsy
A biopsy may be done occasionally for one of the following reasons:
to identify a specific disease process and determine whether it will respond to treatment
to evaluate the amount of damage that has occurred in the kidney
to find out why a kidney transplant may not be doing well
A kidney biopsy is performed by using a thin needle with a sharp cutting edge to slice small pieces of kidney tissue for examination under a microscope.

28. Urine Tests
Some urine tests require only a couple of tablespoonfuls of urine. But some tests require collection of all urine produced for a full 24 hours. A 24-hour urine test shows how much urine your kidneys produce in one day. The test also can give an accurate measurement of how much protein leaks from the kidney into the urine in one day.

29. MICROALBUMINURIA
This is a more sensitive dipstick test, which can detect a tiny amount of protein called albumin in the urine.
People who have an increased risk of developing kidney disease, such as those with diabetes or high blood pressure, should have this test if their standard dipstick test for proteinuria is negative.

30. Albuminuria-to-creatinine ratio (ACR).
Albuminuria occurs when there are higher amounts of a type of protein called albumin in the urine, It is a common marker of kidney damage. The ratio of albumin-to-creatinine is recommended as the best method to determine albuminuria.
All patients with CKD should be tested for albuminuria at least annually.
You should also get tested if you are at risk for kidney disease (have diabetes, high blood pressure, or family history of diabetes, high blood pressure or kidney failure).