Every patient who places himself under the care of a dentist is a potential bearer of any disease known to man. Many of these diseases are diagnosed through information derived from laboratory tests. In hospital work particularly, a knowledge of these tests is essential, but many of them can be performed in the dental office on an outpatient basis. The literature is filled with laboratory experiments, but t is difficult to find in a condensed form a brief outline of tests which detists may be called upon to use. I have therefore attempted to list these tests with such information as is of special interest to the dental diagnostician.

1. Hematology

A. Counting

1. Red Blood Cells.

The normal values vary from 4,500,000 to 6,000,000 erythrocytes per cubic millimeter, being lower in women and children than in men.

Principle: Blood is diluted with an isotonic solution, and the red blood cells are counted in a hemocytometer chamber under a microscope.

The red cell count is increased in primary polycythemia vera and secondary polycythemia (heart disease, pulmonary disease, and condition resulting in decreased oxygen tension of the blood, that is, arteriovenous fistula, high altitudes, etc). It is decreased in most anemias.

Comment: From the most reliable estimates, the standard of error of the red cell count lies between 8 and 10 per cent.

2. White blood cells.

The normal count is 5000 to 10000 cells per cubic millimeter.

Principle: Blood is diluted with acid stain which lakes the red cells and stains the white cells.

The white cell count is high in the presence of most inflammatory and toxic processes (pyogenic infections with staphylococcus and streptococcus), leukemic processes, and trauma (including bone fractures). It is low in the presence of specific infections (such as typhoid fever), and it is notoriously low in aplastic anemia and drug intoxication.

Comment: Persistent and severe leukopenia necessitates a thorough hematologic investigation, as it may indicate systemic disease or bone marrow damage. The same applies to a leukocytosis.

3. Thrombocytes (Platelets)

The normal range number is from 200,000 to 500000 per cubic millimeter.

Principle: The blood is diluted with a fluid containing preservative and an anticoagulant and then stained with methylene blue.

Interpretation: This test is often used for discovering thrombocytopenic purpuras whose only symptoms have been inexplicable gingival bleeding and/ or oral petechiae in areas not normally traumatized. It is also a simple and inexpensive method of following the progress of thrombocytopenic purpuras, aplastic anemia, and leukemias after treatment has begun.

The platelet count is raised in polycythemia, after splenectomy, following severe hemorrhage, and in the presence of leukemia. It is lowered in cases of thrombocytopenic purpuras, severe infections, late leukemia, and aplastic anemia.

Comment: If thrombocytopenia exists, then operative procedures should be deferred until adequate platelets are present. A severe persistent thrombocytopenia is a sign of systemic disease and deserves further hematologic study.

4. Blood smear for differential count

Method: A drop of venous blood is dropped onto a clean slide and spread across with another slide having the drop in back of a sweeping stroke. It is dried and stained with Wright's stain.

Interpretation: In a differential count, the predominant leukocyte and its relative maturity may be noted; the size, shape, maturity, and capacity of the red blood cells can also be evaluated.

Normal white cell values are as follows: neutrophils, 54 to 62 per cent; lymphocytes, 25 to 33 per cent; immature leukocytes (bands), 3 to 5 per cent; monocytes, 3 to 7 per cent; eosinophils, 1 to 3 per cent; and basophils, 0 to 1 per cent.

Mature and immature leukocytes may be identifiable in peripheral blood smears in the presence of leukemia and other hematologic disorders. An excess of a certain type of leukocytes can be a measure of disease, as shown in Table I.

Comment: Although classification is not complete, the value of the differential count cannot be overemphasized. Both total and differential white counts are excellent tools in following the course of the diseases listed in Table I.

B. Hemoglobin determination.

The normal value is 14.5 grams per 100 ml., but values of from 11 to 18 are considered within the normal range.

Principle: The test utilizes the photoelectric method or the colorimetric system, both of which register the color intensity of the blood.

Interpretation: The test is an indication of the oxygen-carrying capacity of the blood, and it is sufficient to say that it is low in all anemias (secondary or primary) and high in the same conditions in which the erythrocyte count is elevated. The value should not be expressed in percentages.

Table 1

Comment: Surgery should be delayed when hemoglobin values fall below 10 Gm./100 ml.

C. Hematocrit (Packed Cell Volume).

The normal value is 35 to 50 per cent.

Principle: A fixed volume of whole blood is placed in a graduated tube and centrifuged, and the per cent volume of packed red cells is measured.

Interpretation: The packed cell volume is also a measure of the relative oxygen-carrying capacity of the blood, and the increased and decreased values in disease correspond to those of hemoglobin.

Comment: This test is easily performed and requires a minimal amount of equipment and technical skill. Values of less than 32 present a general anaesthetic risk.

D. Sedimentation risk.

This is expressed as the rate, in millimeters, at which the blood settles out after one hour, the normal being 3.7 mm for men and 9.6 mm for women, with a maximal range to 20 mm.

Principle: The test measures the velocity of erythrocyte sedimentation, this rate being increased in many diseases.

Interpretation: The sedimentation rate is nonspecitif; there is a rise in the sedimentation rate in any disease in which there is inflammation, tissue degeneraton, suppuration, or necrosis. It is useful in following responses to infections and in differentiating the neuroses from organic disease. If the patient is anemic, some authorities feel that a corrected sedimentation rate is necessary, but Wintrobe believes that the correction of sedimentation rate should be abandoned.

E. Bleeding time.

The normal range varies from one to six minutes.

Principle: This is a means of demonstrating the normal capillary function, and it is a reflection of the function and the number of platelets.

Test: There are 3 types pf tests
(1) the finger-tip pierce.
(2) the ear lobe pierce (Duke method).
(3) the Ivy method.

The Ivy method is more time-consuming, but it is by far the most accurate.

Ivy method procedure: A cuff is placed on the forearm and inflated to register 40 mm. Hg, and the skin of the forearm is pierced with a 4 mm hemolet. The drops of blood are absorbed away with filter paper at thirty-second intervals until bleeding has ceased.

Interpretation: A short bleeding time is of no clinical significance. The test should be discontinued at the end of fifteen minutes in those patients in whom there are no signs of cessation at that time, as further bleeding adds no additional information and has a bad psychic effect on the patient. Bleeding time is prolonged in cases of thrombocytopenia, hereditary capillary defects, and defects in platelet function.

Comment: Bleeding time is nomal in hemophilia and related diseases.

F. Capillary fragility test (Rumpel-Leede's test)

Principle: This test is nonspecific for capillary resistance and involves an increase in the hydrostatic pressure of the capillaries.

Test: A tourniquet is adequate, but an inflated cuff is desirable for standardization. The cuff is inflated to a point midway between systolic and diastolic pressure. If petechiae appear before ten minutes, the test is reported as positive. The test is positive in thrombocytopenia, capillary purpuras, scurvy, and senility.

G. Clotting time (Coagulation time).

The normal is eight to twelve minutes.

Principle: This is simply a test-tube test for the blood's ability to clot. There are two types of tests.
(1) the capillary tube method, which employs a skin capillar and is generally considered unsatisfactory
(2) the Lee-White method, which utilizes venous blood and is the more accurate.

Procedure: Venous blood, 1 cc, is placed in three test tubes wet with saline. The first tube is tilted gently at thirty-second intervals until blood no longer flows down the side of the tube; then the thirty-second tilting is begun on the next two tubes in succession until clotting occurs. The time at which blood clots in the last tube, beginning from the time blood was removed from the vein, is reported as the clotting time.

Interpretation: An increased value indicates a clotting defect, but a normal test does not rule out the possibility of the patient's being a bleeder. The clotting time is increased in AHG, PTC, and PTA and a deficiency of the stable and labile factors; fibrinolytic disease; and hypothrombinemia.

Comment: The clotting time is normal in thrombocytopenia.

H. Clot Retraction.

Normally, clot retraction begins in thirty to sixty minutes and is complete in twenty-four hours.

Principle: The 'pulling away' or retracting of a clot in a test tube varies in health and disease.

Interpretation: The beginning of clot retraction is established when a visible dimpling of clot surface occurs with extrusion of a tiny droplet of serum and is complete when the clot is distinct from the serum. The same tubes that are used for estimation of clotting times may be used for this test. The test is dependent upon blood platelets and plasma-coagulation factors. The character of the clot should also be noted, as poorly formed, friable clot is an indication of disease.

Clot retraction is prolonged in thrombocytopenic states and liver disease.

Comment: This test is normal in patients with hemophilia and related diseases, even though their clotting time is prolonged.

I. Prothrombin time.

The normal is thirteen to fourteen seconds.

Principle: Prothrombin is a carbohydrate containing protein formed in the liver, vitamin K is necessary for its synthesis.

Interpretation: The test utilizes all other clot mechanism factors (calcium, thromboplastin, etc) in correctly established amounts leaving prothrombin as the only variable. This test, the one-stage method of Quick, measures the entire clotting process except for the platelet hemophiliac factor; consequently, the result is normal in hemophilia and related bleeding diseases.

Prothrombin time is prolonged in the presence of cirrhosis and any obstructive jaundice where vitamin K formation is impaired, following trauma of surgery with blood loss (death may be due to acute prothrombine loss), and in eases of deficiency of the prothrombin complex.

Comment: This test is of value in following patients who are receiving anticoagulant therapy with the coumarin group of drgs (Dieumarol).

J. Prothrombin consumption (serum prothrombin time).

Principle: Normally, in clotting, prothrombin is almost completely consumed (80 to 90 per cent), leaving serum with litle residual prothrombin. If there is a deficiency of thromboplastin in the blood, consumption of prothrombin is diminished, leaving a high prothrombin residual in the serum.

Principle of the test: The amount of prothrombin converted into thrombin and the amount of residual prothrombin that remains in the serum after coagulation vary with the amount of thromboplastin and prothrombin that is available.

Interpretation: A serum prothrombin time greater than twenty seconds is normal, indicating that most of the prothrombin has been used. A value lower than this indicates that an abnormal amount of prothrombin is removed.

Prothrombin consumption is abnormal or decreased in AHG, PTC, and PTA deficiency, thrombocytopenic states, and deficiency of the accelerator substances.

K. Antihemophiliac globulin, Plasma thromboplastin antecedent, Plasma thromboplastin component differentiation.

AHG deteriorates after forty-eight hours in plasma, and PTA and PTC do not. Of the remaining two, PTC is absorbed by barium sulfate whereas PTA and AHG are not. With this principle, therefore, these three states can be identified.