III. Urine

A. Examination

1. Volume: The average normal volume is 1,500 cc in a twenty-four-hour period. Any variation from this may indicate renal, bladder, or prostatic disease. Variations also may include diabetes, blood-transfusion reactions, and shock.
2. Specific gravity: This may be conveniently established by the urinometer. It is a measure of the relative amount of solids in solution and is indicative of the degree of tubular reabsorption. It varies inversely with the volume of urine excreted; therefore, renal damage usually may be ruled out if the specific gravity is high. In the presence of renal pathology, the specific gravity remain fixed. The normal is 1.029 to 1.032.
3. Turbidity: A cloudy white is usually a sign of pus in the urine, and a smoky red may indicate the presence of blood.
4. Color: The normal color is clear to yellow, and other colors are indicative of disease.
5. Reaction: Normal urine is acid in reaction and is influenced by diet. Urinary infections may produce an alkaline reaction. This test is easily and inexpensively performed with litmus paper.

B. Microscopic examination

1. Red blood cells

Normally, a red blood cell appears per low-power field.

Abnormally high amounts are found in uncatheterized specimens taken during menstruation and in bleeding from the genitourinary tract (renal calculi, renal infarction, glomerulonephritis, renal malignancy, thrombocytopenic states, and trauma).

Comment: In continued sulfa therapy, the presence of red blood cells may indicate renal damage.

2. Pus cells

These may be seen in centrifuged urine in cases of urinary tract infection (pyelonephritis, eystitis, and urethritis).

3. Epithelial cells

A few normally exist per low-power field, and they are thought to be derived from the renal tubules, bladder, and renal pelvis.

4. Casts

It is normal for a few casts to exist. Abnormally high amounts are found in glomerulonephritis, heart failure, and some diseases of pregnancy.

C. Urine protein.

This is chiefly a test for albumin, but some globulins do exist.

Usual procedure: Glacial acetic acid and water are added to urine. If the urine is cloudy, then albumin is present; the greater the cloudiness, the larger the amount of albumin. High amounts of albumin are found in febrile diseases, heart failure, kidney disease, urinary tract tumors, and malignant hypertension.

D. Clinitest for Sugar.

The commercial Clinitest tablet is dropped into 1 cc of urine and 15 seconds after boiling it is read as follows:

E. Urine sugar (qualitative).

Two methods are in wide use - Feling's test and Benedict's test

1. Fehling's test:
   Fehling's solution is added to urine and boiled. If the test is positive, the solution assumes an opaque yellow and red sediment forms at the bottom of the test tube.
2. Benedict's test:
   Benedict's reagent is added to urine, then boiled and cooled. The interpretation is made from the same colors and grading as in the Clinitest for sugar.

Interpretation: Other than diabetes, increased values are found in pancreatic disease, hyperthyroidism, pituitary disease, severe infections, and brain damage.

Comment: The presence of glycosuria is dependent upon:

1. the concentration of carbohydrate in the blood,
2. the rate of glomerular filtration
3. the degree of tubular reabsorption. The renal threshold is 160 to 180 mg per 100 ml, and then sugar spills over into the urine.

F. Urine calcium determinations (Sulkowitch test)

Principle: This depends on the precipitation of calcium as insoluble calcium oxalate.

Method: Urine and Sulkowitch reagent are mixed and allowed to stand two to three minutes and calcium precipitates out. The precipitate varies from a fine, white, cloudy appearance to a very heavy precipitate and may be graded 1, 2, 3, 4. A trace is normal.

Indications: A decalcification of previously normal skeleton may result in abnormal amounts of calcium in the urine. It is of prime importance in the study of bone disease.

The test is positive in hyperparathyroidism and in disease in which there is rarefaction of the skeleton. It is negative in tetany, rickets, and sprue.

Comment: For best results, a number of specimens should be taken at different hours, since varying amounts are excreted in each voiding. It may also be of value to know the calcium intake.

SUMMARY

Twenty-nine tests in laboratory hematology, blood chemistry, and urinalysis are presented; some, such as the red and white counts, hemoglobin, urinalysis, etc., are used routinely, but others are less frequently employed. No new concepts are offered, but an attempt has been made to present, in a condensed, practical form, laboratory tests that are specifically useful for dentists in office and hospital practice.