Acetone Bodies

Acetone Bodies
The acetone bodies in urine include acetoacetic and hydroxyl butyric acids in addition to acetone.
a.Rothera s test for acetone and acetoacetic acid
Take 3 ml of urine in a test tube and fully saturate ammonium
Sulphate. This is to precipitate and remove proteins which may interfere with the test. Add 1 or 2 crystals of sodium nitroprusside. Mix well and add liquor ammonia. A permanganate coloured ring indicates the presence of acetone and acetoacetic acid.
b. Gerhardt s test for acetoacetic acid
To 5 ml of urine add 10% FeCl3 solution drop by drop till a maximum precipitate of ferric phosphate is obtained. This is to eliminate the phosphate which may otherwise obscure the colour in the test. Filter and to the filtrate add excess of FeCl3. A Bordeaux wine red colour indicates the presence of acetoacetic acid in urine.
FORMAYION OF URINE
The kidney not only excretes the non-volatile metabolic waste materials of the body but also maintains the homeostasis of the body fluids. The kidney function is made up of the following four processes:

1. Filtration of protein free plasma by glomeruli
2. Selective reabsorption by the tubule
3. Secretion by the tubule
4. Maintenance of acid-base balance.
Urine is formed as a result of these four processes. A large volume of blood, approximately 1 litre / minute flows through the kidneys. The filtrate contains all other constituents of plasma except the proteins. It contains many substances necessary for normal metabolism such as water, glucose, amino acids and chlorides as well as substances to be rejected such as urea, creatinine and uric acid. Substances which are necessary for the body are reabsorbed by the tubule along with nearly 99% of the water of the filtrate. Certain other substances are added to produce the final urine which is passed out into the bladder at the rate of about 1 ml per minute.
RENAL FUNCTION TESTS
The kidneys are the major excretory organs and they also maintain the acid – base , fluid and electrolyte balance . Therefore it is very important to detect any abnormal function of kidney as early as possible .
Renal functions tests are grouped into 3:
1. Routine clinical tests which include , ( a) complete urinalysis , (b) measurement of NPN in blood , (c) measurement of serum electrolytes .
2. Tests done for detailed assessment are , (a) clearance tests (b) urinary and plasma osmolality , and (c) concentration and dilution tests .
3. Tests done for specific diagnosis or research purposes .
Test of Glomerular Function
The glomerular filtration rate (GFR ) depends on the net pressure being exerted across the glomerular membrane ; the physical nature of the membrane and the surface area of the membrane . GFR gives an index of the number of functioning glomeruli . This can be evaluated by :
a. Urea clearance test
b. Inulin clearance test
c. Creatinine clearance test
Glearance test
The clearance of any substance is defined as the number of ml plasma / blood which contains the amount of that substance excreted in one minute by the kidneys .


Blood Urea and Urea Clearance Test
The normal blood urea level ranges from 20 to 40 mg per 100 ml . Urea clearance is the volume of plasma cleared of urea per minute .
UxV
Urea clearance =
B
Where U = Concentration of urea in urine (in mg / 100 ml)
V= Volume of urine ( in ml / mt )
B= Concentration of urea in blood ( in mg / 100 ml )
Maximum Urea clearance
Normal maximum urea clearance is 75 ml per minute . When the volume of urine excreted per minute is 2 ml or more , urea clearance is maximum .
Standard urea clearance
When the urinary volume is less than 2 ml / mt the urea clearance is reduced . Such clearance is termed as standard clearance and the average normal value is 54 .
Procedure for urea clearance test
The patient is asked to take a light breakfast with two glasses of water. The first sample of urine passed after the water intake is discharged. Time is noted. Two urine samples are collected at 1 hour interval along with two blood samples. Urea clearance is calculated using the formula UV / B. In severe renal failure the clearance falls below 20% of the average normal.


Greatinine Clearance Test
Creaatinine clearance is more than 100 ml / min in healthy adults . Creatinine clearance measurements correlate fairly closely with inulin clearance measurements except in patients in whom GFR is severely impaired . Because a portion of creatinine is secreted by tubules , the clearance value is slightly raised .
Procedure
24 hours urine is to be collected . At the start of the collection period , usually at 8 AM the patient is instructed to empty the bladder and to discard the specimen . After this , all the urine samples are collected and placed in toluene ( preservative ) till 8 AM the following day . The volume of pooled urine is noted . A specimen of blood is collected during the period of urine collection . Creatinine clearance is calculated by using the formula
UV
B
The creatinine clearance is impaired in acute and chronic renal failure .
Inulin Clearance Test
This test is done to find glomerular filtration rate (GFR). Inulin is filrated by the glomeruli but neither secreted nor absorbed by the tubules. The amount of inulin excreted in each minute is the amount filtered by the glomeruli. The concentration of inulin in the glomerular filtrate is equal to that in the plasma. Thus the clearance value of inulin is the same as glomerular filtration rate.
During the period of urine collection, a constant plasma inulin level is maintained by intravenous drip. The normal inulin clearance value is about 125 ml per minute.
URINE CONCENTRATION TEST
This designed to test the concentration power of the kidneys. The capacity of the kidneys to concentrate urine is a sensitive test to detect early loss of kidney function . the test is simple as it does not require any laboratory facilities . At 6 p.m. give the patient , a meal with good protein content but not more 200 ml of fluid to drink . Allow no more fluid after this meal . Discard any urine passed during the night . On the following morning collect three samples of urine as follows :
8AM – Urine sample I
9AM- Urine sample II
10AM – Urine sample III
Measure the specific gravity of the all samples . The specific gravity of at least one specimen should exceed 1.022 . A maximum specific gravity of less than 1.022 indicates impaired renal function . When the kidney loses its capacity to do osmotic work , the urinary solids must be excreted in more dilute solution . The advantage of this test is that it is useful for the detection of renal defect when the blood urea is normal .
DILUTION TEST
In addition to the loss in power of the kidneys to produce concentrated urine , there is also an impairment in its ability to excrete dilute urine . In this test , no water is taken after midnight , the bladder is emptied at 7 a.m. and the patient is given 1200 ml of water to drink in 30 minutes . Urine samples are collected hourly for next four hours , i.e. at 8,9,10 and 11 a.m. The volume and specific gravity of each specimen are noted . Specific gravity of at least one sample should fall to 1.003 or below . Almost all the water drunk (1200 ml ) should be excreted within those 4 hours . When renal impairment is severe, volume may be less than 100 ml with the specific gravity of 1.010 or more .
Phenol Sulphonphthalein ( PSP ) Test or Phenol Red Excretion Test for Kidney Function
The PSP test indicates a general loss of kidney function . The dye is nontoxic and is exclusively excreted by the kidney . After intravenous injection of the dye , the 15 minutes sample collected should 25 % or more of the injected dye which is estimated calorimetically .


Measurement of Renal Blood / Plasma flow
Renal blood flow can be determined by using paraamino hippuric acid , which at low blood concentration is removed entirely by the tubular excretion in a single circulation through the kidney . It is a measure of the plasma flow which is normally 574 ml per minute per 1.73 sq .m. body surface area .