In one sense, all laboratory tests are used as a guide to treatment, since they promote accurate diagnosis. In this section, however, reference is made to the use of laboratory tests to select the type of treatment to be used, to determine how much treatment is required, to confirm that the desired effect is being obtained, and to avoid harmful side effects of treatment. The need for tests of this type is greatest in those chronic diseases where treatment must be continued for a long time, perhaps for life.
Tests of Antibiotic Efficacy
In a dangerous infection such as meningitis, it is extremely important to obtain an optimum therapeutic effect without delay. Since meningitis may be due to different bacteria, and each of these may respond differently or not at all to the various antibiotic drugs, it is common practice to test the various antibiotic drugs directly against the bacteria that are present in the particular case. This can be done in the following way:
Spinal fluid from the patient is mixed with melted agar in a sterile dish and the warm mixture is allowed to cool and solidify. Tiny paper disks, each of which has been impregnated with a different antibiotic, are dropped onto the surface of the agar and the dish is set aside for several hours in an incubator. The bacteria that were present in the patient’s spinal fluid begin to multiply and form “colonies” in the medium, except that where they are in contact with the paper disks their growth may be modified by the antibiotic.
If all bacterial growth is suppressed about the paper disk saturated with tetracycline, but growth is abundant about the disk saturated with penicillin, it is clear that tetracycline is a better drug than penicillin to use in the treatment of this particular patient with meningitis. The test is a combination of spinal fluid culture and antibiotic sensitivity.
Dosage Regulation
Probably the oldest use of laboratory tests to regulate drug dosage is in the diabetic patient. Some diabetics have a different requirement of insulin from day to day, depending upon appetite, diet, exercise, colds and the like. If the regular dose of insulin is sufficient, the urine test for glucose will be negative. If it is insufficient, the test may give a green, yellow or red color, depending upon the amount of glucose present. The doctor teaches the patient how to test his own urine and to regulate the dose of insulin depending upon the color of the urine test. From time to time the diabetic patient must also have a glucose test on blood, so as to avoid over dosage of insulin.
The following are other examples of the use of laboratory tests to guide treatment. After an attack of coronary thrombosis, many patients are given drugs to reduce the clotting tendency of their blood. The effect must be precisely controlled by coagulation tests, since overdose of the drug could cause a tendency to hemorrhage.
X-rays, radium and drugs used in the treatment of cancer sometimes destroy blood cells as well as cancer cells; occasional counts must be taken of white cells, red cells and platelets to make sure that this harmful effect is avoided. Some drugs used in the treatment of high blood pressure produce in some patients a condition resembling a special form of sensitivity disease known as lupus eurhythmics,. special blood examinations (“LE prep”) can anticipate this effect.
Transfusions
Of life-saving importance in certain diseases is the use of blood transfusions. However, different people have different types of blood and it would be extremely dangerous to give a patient blood of a type different from his own. To detect these types and determine compatibility between donor’s and recipient’s blood, blood group and Rh tests must be carried out meticulously.
Similar tests (blood group and Rh) are of importance in determining whether the blood of an unborn baby is compatible with that of its mother. If incompatibility is present, it may be necessary to give the baby an “exchange transfusion” immediately after birth.
Frozen Section
The surgeon often calls upon the pathologist to help him decide whether a lump in the breast should be simply removed or whether the whole breast and the nearby lymph nodes should also be removed. This test, known as the “frozen section,” is performed while the patient is under anesthesia. The surgeon removes the lump and passes it to the pathologist who freezes a portion of it in a jet of carbon dioxide gas. Once frozen, a very thin slice or section is cut, stained with a dye, mounted on a glass slide and examined under the microscope. If cancer is present, as determined by the pathologist, the surgeon will normally remove the entire breast and related tissue so as to “get around” the cancer. If the pathologist determines that the lump is benign, the surgeon ordinarily does not remove the remainder of the breast
Tags:antibiotic drugs, antibiotic sensitivity, desired effect, laboratory tests, tetracycline therapeutic effect