Chemical analysis of urine

CHEMICAL ANALYSIS

Chemical analysis of urine helps to determine the presence of abnormal constituents of urine or presence

of normal constituents in abnormal quantity. Both the findings reveal the presence of renal abnormality.

Following are the common chemical tests of urine:

1. Glucose

Glucose appears in urine when the blood glucose level increases above 180 mg/dL. Glycosuria (presence of glucose in urine) may be the first indicator of diabetes mellitus.

2. Protein

Presence of excess protein (proteinuria) particularly albumin (albuminuria) in urine indicates renal diseases. Urinary excretion of albumin in a normal healthy adult is about 30 mg/day. It exceeds this level in glome rulonephritis. It also increases in fever and severe exercise.

3. Ketone Bodies

Ketonuria (presence of ketone bodies in urine) occurs in pregnancy, fever, diabetes mellitus, prolonged starvation and glycogen storage diseases.

4. Bilirubin

Bilirubin appears in urine (bilirubinuria) during hepatic and posthepatic jaundice.

5. Urobilinogen

Normally, about 1 to 3.5 mg of urobilinogen is excreted in urine daily. Excess of urobilinogen in urine indicates hemolytic jaundice.

6. Bile Salts

Presence of bile salts in urine reveals jaundice.

7. Blood

Presence of blood in urine (hematuria) indicates glomerulo nephritis, renal stones, infection or malignancy

of urinary tract. Hematuria must be confirmed by microscopic examination since chemical test fails to distinguish the presence of red blood cells or hemoglobin in urine.

8. Hemoglobin

Hemoglobin appears in urine (hemoglobinuria) during excess hemolysis.

9. Nitrite

Presence of nitrite in urine indicates presence of bacteria in urine since some bacteria convert nitrate into nitrite in urine.

EXAMINATION OF BLOOD

1. Estimation of Plasma Proteins

Normal values of plasma proteins:

Total proteins : 7.3 g/dL (6.4 to 8.3 g/dL)

Serum albumin : 4.7 g/dL

Serum globulin : 2.3 g/dL

Fibrinogen : 0.3 g/dL

Level of plasma proteins is altered during renal failure.

2. Estimation of Urea, Uric Acid and Creatinine

Normal values :

Urea : 25 to 40 mg/dL

Uric acid : 2.5 mg/dL

Creatinine : 0.5 to 1.5 mg/dL

The blood level of these substances increases in renal failure.

EXAMINATION OF BLOOD AND URINE

Plasma Clearance

Plasma clearance is defined as the amount of plasma that is cleared off a substance in a given unit of time. It is also known as renal clearance. It is based on Fick principle.Determination of clearance value for certain substances helps in assessing the following renal functions:

1. Glomerular filtration rate

2. Renal plasma flow

3. Renal blood flow.

Value of following factors is required to determine the plasma clearance of a particular substance:

1. Volume of urine excreted

2. Concentration of the substance in urine

3. Concentration of the substance in blood.

Formula to calculate clearance value

U V

C =

P

Where, C = Clearance

U = Concentration of the substance in urine

V = Volume of urine flow

P = Concentration of the substance in plasma.

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