Thursday, April 27, 2017

A Brief Discussion On Urinalysis

Urinalysis means examining or testing the urine and it is one of the most common and easy method used for medical diagnosis. It involves the physical, chemical, and microscopic examination of urine.

A part of a urinalysis can be performed by using urine test strips, known as Dipstick in which the test results can be read as color changes. Another method is examination of the urine sample under light microscopy.

Physical Or Macroscopic Examination Of urine
The first part of a urinalysis is direct visual observation:

1. Colour
Normal color of the urine ranges from colorless to deep yellow depending on the concentration of the urochorme pigment. Different colors may be observed in different conditions like red with blood in the urine or certain food colors e.d beetroot. orange with rifampicin, yellow in jaundice or dehydration and black with severe hemoglobinuria.

2. Volume
Normal volume is 800-2600 ml/day and it is referred to be oligouria if its < 300 ml/day and anuria if < 100 ml/day.

3. Appearance
A normal urine sample appears clear on visual inspection. Turbidity or cloudiness may be caused by excessive cellular material or protein in the urine or may develop from crystallization or precipitation of salts upon standing at room temperature or in the refrigerator. Clearing of the specimen after addition of a small amount of acid indicates that precipitation of salts is the probable cause of tubidity.

Urine Dipstick Chemical Analysis

1. Specific Gravity
Normal range is 1.000 to 1.030. It varies with the quantity of urine and a persistently low specific gravity suggests chronic renal failure or diabetes insipidus while a high specific gravity suggests dehydration.

2. pH
Fresh urine specimen is acidic with an average pH of 6 and a normal range of 4.5-8. The pH is usually important in investigation and management of renal tubular acidosis. Infection with urea splitting organism Proteus causes alkaline urine that favors renal stone formation.

Normal protein loss from urine is 150 mg/24 hrs and it may sometimes rise upto 300 mg/24hrs in fever or with exercise. Other common causes of proteinuria are nephrotic syndrome, diabetic nephropathy, hypertention and certain infections e.g Hepatitis B, HIV etc.

Glucose in urine usually indicates diabetes but it may be due to certain other cause that includes renal tubular damage, sepsis, low renal threshold in chronic renal failure and fanconi’s syndrome. False results may be observed if patient is taking large doses of Vitamin C. tetracylines or levodopa.

5. Ketones
Presence of ketones is seen in diabetic ketoacidosis and in starvation.

6. Nitrites
Important indicator of UTI and also seen when a person takes a high protein meal.

7. Billirubin
It is positive in obstructive jaundice.

Urine Microscopy
A drop of fresh urine covered with a cover slip is observed under the light microscope and may reveal important diagnostic information.

1. White Cell or Leucocytes
More than 10/mm3 in an unspun urine specimen is abnormal. causes include cystitis, urethritis, prostatitis, pyelonephritis, renal calculi, interstitial nephritis, tuberculosis.

2. Red cells
More than 2/mm3 in an unspun urine specimen is abnormal. It can also be detected as a positive test for hematuria on dipstick. Common causes include IgA nephropathy, glomerulonephritis, polycystic kidneys, papillary necrosis, renal calculi, UTI, sickle cell disease, trauma, drug cyclophosphamide.

RBC’s of glomeruli origin tend to be dysmorphic with many sizes and shapes whereas those of non glomeruli origin are uniform in size and shape.

3. Casts
Casts are cylindrical bodies found in the lumen of distal tubules and they may be of many types including hyaline, granular, white cell casts, red cell casts, epithelial casts or broad waxy casts.

4. Crystals
Crystals are common in cold or old urine and usually do not signify any pathology but presence of certain crystals are important for example cystine crystals are diagnostic of cystinuria and oxalate crystals in fresh urine is an indicator for increased possibility for stone formation.

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