It is important to realize the limitations of any laboratory test. There are no tests that can detect “health”; rather, laboratory tests are used to discriminate between the presence or absence of disease or are used as a predictor of disease. The frequency with which a test indicates the presence of a disease is called sensitivity; specificity is the frequency with which a test indicates the absence of the disease.
A test that identifies a disease every time has a sensitivity of 100% whereas a test that identifies the absence of disease every time has a specificity of 100%. Consequently, a test with a sensitivity of 98% has a 2% false-negative rate, and a test with a specificity of 98% has a 2% false-positive rate. The significance of choosing a test with a particular sensitivity or specificity usually corresponds with the outcome of the test result. For instance, it is highly desirable to use an HIV test with a high sensitivity to minimize false-negative results because individuals who believe they are HIV-negative may continue to transmit the disease and may not seek medical care. However, sensitivity improves at the expense of specificity, and vice versa.
Another important aspect of a test is its efficacy, or predictive value. Predictive value is defined as the value of positive results indicating the presence of a disease (positive predictive value) or the value of negative results indicating the absence of a disease (negative predictive value). These predictive values are dependent on the prevalence of the particular condition in the population, as well as on the sensitivity and specificity of the test.
Even normal values in tests used to screen asymptomatic populations for disease fall within two standard deviations of the mean. Consequently, a single test will produce an abnormal result 5% of the time. For a “panel” of tests the percentage of abnormal results increases significantly. Thus, for any decision (or even diagnosis) based on any laboratory test, many different criteria need to be considered.
Laboratory studies are an extension of the physical examination; tissue, blood, urine, or other specimens are obtained from the patient and are subjected to microscopic, biochemical, microbiologic, or immunologic examination. A laboratory test alone rarely establishes the nature of an oral lesion, but when interpreted in conjunction with information obtained from the history and the physical examination, the results of laboratory tests will frequently establish or confirm a diagnostic impression. Specimens obtained directly from the oral cavity (eg, scrapings of oral mucosal cells, tissue biopsy specimens, and swabs of exudates), as well as the specimens more commonly submitted to the clinical diagnostic laboratory (eg, blood), may provide information that is of value in the diagnosis of oral lesions such as candidiasis, pulpal and periodontal abscesses, pharyngitis, and lesions of the oral mucosa and jaw bones.
Lesions of the oral cavity may also be complicated by coexistent systemic disease or may be the direct result of such disease. Many of the laboratory studies needed in dental practice are those that are widely used in medicine. The systemic disease suspected by the dentist may often be of greater significance to the patient’s health than the presenting oral lesion may be. By investigating a problem of this type, the dentist is, in effect, investigating a medical problem. It has been argued that the patient in whom systemic disease is suspected should be referred to a physician without further tests being ordered by the dentist. This procedure is clearly the correct one under some circumstances, and professional judgment is required. However, in many situations, laboratory studies made by the dentist prior to medical referral are appropriate and may be necessary to identify the nature of the patient’s problem or to assess the severity of an underlying medical condition.
Diseases affecting the oral cavity often exhibit features peculiar to this region, and a dentist trained in the management of diseases of the oral cavity may be better equipped to select appropriate laboratory tests and evaluate their results than is a physician with no specific knowledge of the region.
A diagnostic problem can be solved by referral only when the patient accepts the referral. If a lesion is minor or if the patient is unwilling to admit that the lesion may be of systemic origin, then she or he may reject the dentist’s advice, delay in following up the referral, or even seek treatment elsewhere. Failure to follow up a referral may sometimes stem from the patient’s belief that the dentist is straying beyond his or her area of competence but is more often the result of anxiety created by the dentist’s suggesting that the patient may have an undiagnosed medical problem. Referral to a physician is possible only when confidence is firmly established between dentist and patient. Patients who seem unwilling to accept referral to a physician often agree to a screening laboratory test (eg, blood sugar, hematocrit) carried out through the dentist’s office. When the results of such tests are positive, they strengthen the dentist’s recommendation and often achieve the desired referral.
Screening diagnostic clinical and laboratory procedures, such as blood pressure measurement, complete blood count, blood chemistry screening, throat culture for infections with beta-hemolytic streptococci, and detection of antibodies to hepatitis viruses and HIV, have also been used for epidemiologic purposes in dentistry.
48–51
Except in limited situations, however, the cost of standard screening tests such as a complete blood count or blood sugar determination has discouraged their routine use in dental offices and clinics, even though the detection of elevated blood pressure has become customary.
The results of screening tests of this type (and, in fact, the majority of studies carried out by dentists for the detection of systemic diseases) do not themselves constitute a diagnosis. For example, a dentist who finds glucose in the blood of a patient should not tell the patient that he or she has diabetes but should inform the patient that the results of the test indicate an abnormality and should then advise the patient to seek medical consultation. Reports of abnormal results for any of the tests should be sent directly to the patient’s physician, and the diagnosis of diabetes, hypertension, or other disease should be made by the physician on the basis of physical examination, history, and (possibly) further laboratory tests. The management of any systemic problem detected is also the prerogative of the physician, and the dentist should not consider prescribing medication or other treatment for systemic disease detected in this way, even though he might be required to provide local care for the oral manifestations. The physician may decide that in the latent stage of the disease, only surveillance and advice to the patient are required.
The success of all screening for systemic disease, whether carried out by the public health authorities or by dentists, depends on the availability of physicians who are willing to accept such referrals. When ordering or carrying out a laboratory test for the detection of systemic disease, always consider what can practically be done with the results of the test. Laboratory testing without follow-up is not only futile but can lead to serious anxiety in the patient.
A test that identifies a disease every time has a sensitivity of 100% whereas a test that identifies the absence of disease every time has a specificity of 100%. Consequently, a test with a sensitivity of 98% has a 2% false-negative rate, and a test with a specificity of 98% has a 2% false-positive rate. The significance of choosing a test with a particular sensitivity or specificity usually corresponds with the outcome of the test result. For instance, it is highly desirable to use an HIV test with a high sensitivity to minimize false-negative results because individuals who believe they are HIV-negative may continue to transmit the disease and may not seek medical care. However, sensitivity improves at the expense of specificity, and vice versa.
Another important aspect of a test is its efficacy, or predictive value. Predictive value is defined as the value of positive results indicating the presence of a disease (positive predictive value) or the value of negative results indicating the absence of a disease (negative predictive value). These predictive values are dependent on the prevalence of the particular condition in the population, as well as on the sensitivity and specificity of the test.
Even normal values in tests used to screen asymptomatic populations for disease fall within two standard deviations of the mean. Consequently, a single test will produce an abnormal result 5% of the time. For a “panel” of tests the percentage of abnormal results increases significantly. Thus, for any decision (or even diagnosis) based on any laboratory test, many different criteria need to be considered.
Laboratory studies are an extension of the physical examination; tissue, blood, urine, or other specimens are obtained from the patient and are subjected to microscopic, biochemical, microbiologic, or immunologic examination. A laboratory test alone rarely establishes the nature of an oral lesion, but when interpreted in conjunction with information obtained from the history and the physical examination, the results of laboratory tests will frequently establish or confirm a diagnostic impression. Specimens obtained directly from the oral cavity (eg, scrapings of oral mucosal cells, tissue biopsy specimens, and swabs of exudates), as well as the specimens more commonly submitted to the clinical diagnostic laboratory (eg, blood), may provide information that is of value in the diagnosis of oral lesions such as candidiasis, pulpal and periodontal abscesses, pharyngitis, and lesions of the oral mucosa and jaw bones.
Lesions of the oral cavity may also be complicated by coexistent systemic disease or may be the direct result of such disease. Many of the laboratory studies needed in dental practice are those that are widely used in medicine. The systemic disease suspected by the dentist may often be of greater significance to the patient’s health than the presenting oral lesion may be. By investigating a problem of this type, the dentist is, in effect, investigating a medical problem. It has been argued that the patient in whom systemic disease is suspected should be referred to a physician without further tests being ordered by the dentist. This procedure is clearly the correct one under some circumstances, and professional judgment is required. However, in many situations, laboratory studies made by the dentist prior to medical referral are appropriate and may be necessary to identify the nature of the patient’s problem or to assess the severity of an underlying medical condition.
Diseases affecting the oral cavity often exhibit features peculiar to this region, and a dentist trained in the management of diseases of the oral cavity may be better equipped to select appropriate laboratory tests and evaluate their results than is a physician with no specific knowledge of the region.
A diagnostic problem can be solved by referral only when the patient accepts the referral. If a lesion is minor or if the patient is unwilling to admit that the lesion may be of systemic origin, then she or he may reject the dentist’s advice, delay in following up the referral, or even seek treatment elsewhere. Failure to follow up a referral may sometimes stem from the patient’s belief that the dentist is straying beyond his or her area of competence but is more often the result of anxiety created by the dentist’s suggesting that the patient may have an undiagnosed medical problem. Referral to a physician is possible only when confidence is firmly established between dentist and patient. Patients who seem unwilling to accept referral to a physician often agree to a screening laboratory test (eg, blood sugar, hematocrit) carried out through the dentist’s office. When the results of such tests are positive, they strengthen the dentist’s recommendation and often achieve the desired referral.
Screening diagnostic clinical and laboratory procedures, such as blood pressure measurement, complete blood count, blood chemistry screening, throat culture for infections with beta-hemolytic streptococci, and detection of antibodies to hepatitis viruses and HIV, have also been used for epidemiologic purposes in dentistry.
48–51
Except in limited situations, however, the cost of standard screening tests such as a complete blood count or blood sugar determination has discouraged their routine use in dental offices and clinics, even though the detection of elevated blood pressure has become customary.
The results of screening tests of this type (and, in fact, the majority of studies carried out by dentists for the detection of systemic diseases) do not themselves constitute a diagnosis. For example, a dentist who finds glucose in the blood of a patient should not tell the patient that he or she has diabetes but should inform the patient that the results of the test indicate an abnormality and should then advise the patient to seek medical consultation. Reports of abnormal results for any of the tests should be sent directly to the patient’s physician, and the diagnosis of diabetes, hypertension, or other disease should be made by the physician on the basis of physical examination, history, and (possibly) further laboratory tests. The management of any systemic problem detected is also the prerogative of the physician, and the dentist should not consider prescribing medication or other treatment for systemic disease detected in this way, even though he might be required to provide local care for the oral manifestations. The physician may decide that in the latent stage of the disease, only surveillance and advice to the patient are required.
The success of all screening for systemic disease, whether carried out by the public health authorities or by dentists, depends on the availability of physicians who are willing to accept such referrals. When ordering or carrying out a laboratory test for the detection of systemic disease, always consider what can practically be done with the results of the test. Laboratory testing without follow-up is not only futile but can lead to serious anxiety in the patient.