Microscopic examination of urine

Microscopic examination of urine

The microscopic examination is a vital part of the routine urinalysis. It is a valuable diagnostic tool for the detection and evaluation of renal and urinary tract disorders as well as other systemic diseases. 

The best specimen for the routine urinalysis is the first morning specimen as it is concentrated and has an acidic environment needed to preserve the cells and casts. The sediment should be examined as soon as possible after collection, but it may be refrigerated for a few hours if the examination cannot be performed immediately.

Procedure: 

1. 10ml of fresh urine is centrifuged at a speed of 1500-2000rpm for 5 minutes.

2. The supernatant fluid is decanted and sediment is resuspended in the urine that drains back down from the sides of the tube.

3.  A small drop of the sediment is placed on a clean slide and covered with a cover slip. 

4. The preparation is focused under low power with the condenser being kept low and the illumination reduced by minimally opening the diaphragm. The high power is used to identify the constituents.

Organized deposits: The main elements which commonly go to form the organized deposits include the various cells (RBCs, WBCs, epithelial cells). Few bacteria, spermatozoa and parasites can also be seen. The artefacts include starch, fibers and hair. 

Cells found in urine: Identified by their morphology

1. WBCs in urine: Refers to pyuria. 0-4 cells/HPF can be seen in normal urine. Results are reported as number of cells/HPF. Increased numbers are seen in:

a. Urinary tract infections

b. High grade fever

c. Chronic pyelonephritis

d. Prostatitis

e. Renal stones and tumors

2. RBC in urine: Implies haematuria. 0-2 RBCs may be present normally. Results are reported as number of cells/HPF. Increased numbers are seen in:

a. Acute glomerulonephritis b. Traumatic conditions

c. Stones of urinary tract d. Tumors of urinary tract

e. Acute febrile illness f. Severe exercise

3. Epithelial cells in urine: Most common elements in normal urine. Morphology helps to note the origin in the genitourinary tract. A few epithelial cells from the bladder may be present in the normal urine, and cells from the vulva and vagina are the usual contaminants of a routine specimen from women, the presence of more than a few epithelial cells in a clean or catheterized  specimen of urine is abnormal and indicates disease of the urinary tract. The cells include

a. Squamous cells: Large flat round to polygonal cells with pyknotic nucleus.

b. Transitional cells: Smaller cells with granular cytoplasm with a tail. Long tail is seen in cells arising from ureter while cells arising from bladder and renal pelvis show a shorter tail.

c. Collecting duct epithelial cells: small round and have granular cytoplasm

Casts in urine: Are tubular or cylindrical structures with parallel borders and rounded ends. Presence of casts is always renal in origin and is indicators of intrinsic renal disease.

The different types of casts in urine include:

• Hyaline casts: They are colorless, homogenous with rounded ends. Small numbers may be found in urine from healthy people. Large numbers are found in all forms of renal diseases (acute glomerulonephritis, malignant hypertension).

• Granular casts: They are granules trapped in a cast. When found in large numbers, indicate tubular degeneration and occur in glomerulonephritis, nephrotic syndromes and nephrosclerosis. 

• Fatty casts: Refractile fat globules found within basic protein matrix. They are found in nephrotic syndrome and lipoid nephrosis 

• Waxy casts: Highly refractile and yellowish in color. Never found in normal urine, presence indicates tubular degeneration. They are found in end stage kidney, chronic renal failure and renal transplant rejection.

• Cellular Casts: These include epithelial casts, leucocyte casts, RBC casts and bacterial casts. The various cellular elements are found trapped in the basic matrix. The causes for their formation are different.

a. Epithelial casts: found in acute tubular necrosis, heavy metal poisoning, renal transplant 

rejection.

b.Leucocyte casts: seen in acute glomerulonephritis, acute pyelonephritis, lupus nephritis.

c. Red cell casts: seen in acute glomerulonephritis, lupus nephritis, Good pasture syndrome, renal infarction

Unorganized deposits: These include the crystals in urine and are identified by their appearance and solubility characteristics

Crystals found in acidic urine:

Uric acid Cystine

Calcium oxalate Leucine

Amorphous urates Tyrosine

Cholesterol

Crystals found in alkaline urine:

Triple phosphates Amorphous phosphates 

Calcium carbonate Calcium phosphate

Ammonium biurates

Crystals in Acidic Urine