Specificity is the ability of the test to identify correctly those who do not have . diabetes. A screening test using a high cut- point will treat the bottom box as normal and will .. Relationship of Disease Prevalence to Predictive Value. Example. that variation with disease prevalence is typically strong for sensitivity and specificity, viduals are classified as hypertensive or normotensive on the basis of the . Relationship of sensitivity, specificity, and the predictive values with disease. - Sensitivity, Specificity, Positive Predictive Value, and Negative Relationship between disease prevalence and predictive value in a test with 95% .
Only one set of readings was not validated due to inconsistent procedure and was excluded from the study. SMBP was considered adequate when four valid readings were recorded in the instrument's memory at the preset time points. The participant's SMBP was calculated as the average of these four readings. For identifying white coat hypertension false positivesmasked hypertension and white-coat effect false negativesthe following combinations of methods were used: In the statistical analysis categorical variables were described as percentages.
The Kolmogorov-Smirnov test was used to assess the normality of continuous variables.
Measures of diagnostic performance sensitivity, specificity, positive and negative predictive values, and accuracy were calculated using h AMBP as the gold standard. All participants signed an informed consent form. Hypertensive participants showed higher mean age Also, both methods showed similar accuracy. Of all participants, 77 Table 2 shows a comparison of the performance of two BP measurement methods to identify white coat hypertension, masked hypertension and white-coat effect.
There were identified seven 2. The method tested for identifying white coat hypertension showed greater specificity than sensitivity, and good diagnostic ability evidences through high accuracy and agreement, and a NPV indicating low false-negative rates.
The results with the same combination SMBP and CMBP used for identifying masked hypertension and white coat effect suggest that a similar performance to that seen for white coat hypertension.
Since SMBP do not follow a standard protocol time points of BP measures and number of steps required to establish the most accurate diagnosis are set at the physician's and patient's discretion. However, the present study allows a comparison of performance of the three methods studied. One limitation of this study is the high number of participants taking antihypertensive drugs, which makes it difficult to know their actual BP but does not preclude a comparison of methods for the diagnosis of hypertension.
The superior results found refers only to aspects related to a method's sensitivity and accuracy and should not be interpreted as an option to replace one method for another as they are described in the literature as being complementary for diagnosing hypertension. Since white coat hypertension, masked hypertension and white coat effect have low prevalence, a test's specificity is the best marker of diagnostic quality.
We did not compare a test's superiority because a single test was used to identify different conditions. It also showed that when appropriately performed SMBP is a feasible, safe and low-cost approach that can help the clinical diagnosis of hypertension. In conclusion, SMBP can be used to help the diagnosis when hypertension is suspected but it cannot replace CMBP, which is still the most reliable method.
The indiscriminate use of SMBP should be discouraged in the general population because it is only helpful when the protocol is followed consistently but most people do not know the correct procedure. Also, some people may carry out a BP measure at times when they feel their "BP is high," increasing their anxiety.
Sensitivity and specificity in the diagnosis of hypertension with different methods
Therefore, the management of hypertension based solely on SMBP is not recommended. Ambulatory blood pressure monitoring and blood pressure self-measurement in the diagnosis and management of hypertension. Statistical Methods for assessing agreement between two methods of clinical measurements.
An international comparative study of blood pressure in populations of European vs. Home blood pressure monitoring in clinical practice: The British Hypertension society protocol for the evaluation of automated and semi-automated blood pressure measuring devices with special reference to ambulatory systems. Blood pressure measuring devices: Comparison of auscultatory and oscillometric blood pressures.
Arch Pediatr Adolesc Med. Recommendations for blood pressure measurement in humans and experimental animals: N Engl J Med. When and how to use self home and ambulatory blood pressure monitoring. J Am Soc Hypertens. Sensitivity indicates the probability that the test will correctly diagnose a case, or the probability that any given case will be identified by the test.
To help you remember the term, being sensitive implies being able to react to something. Specificity is the proportion of persons without the disease who have low scores on the screening test: To help you remember the term, a specific test is one that picks up only the disease in question, so it has a narrow focus, which explains the term 'specific'. Most tests provide a continuous score think of a blood pressure reading ; these are divided into positive or negative results hypertensive or not using a cutting point or threshold.
This could be changed. What happens to sensitivity and specificity if I change the cutting point?
Link to an article in the British Medical Journal that gives a "right brain" approach to sensitivity. You may find this article really helpful if you are having difficulty with this concept. That wasn't so hard. Is there anything else I need to know?
Even if a diagnostic test is very accurate, interpreting it requires some common sense. Predictive values You may have noticed that sensitivity and specificity were calculated beginning from the actual diagnosis "how many of the people who really have the disease does the test identify?
Concepts: Sensitivity, Specificity & Likelihood Ratios
But obviously, as the physician using the test, you don't know who really has the disease: Referring back to the 2 x 2 diagram, you will in effect be looking across the rows a positive or negative score on the test. So sensitivity and specificity do not really apply: Look again at the diagram: Now a crucial fact to grasp is that the positive predictive value varies according to the prevalence of the disease in the population from which your patient comes.
If you are really keen, you can work this out for yourself; the notes from the Critical Appraisal course Module 4, pages 23 and 24 explain how. Or else, you can take the intuitive route, as follows So, a patient may get a positive test result but if the prevalence in the population is very low, because of the small number of true cases mixed in with all those false positives, the test result may not mean very much.
Imagine you are a general practitioner and the disease is relatively rare among your patients.
Screening For Hypertension Annually Compared With Current Practice
The pre-test probability of your patient having a disease will be low, and this will bring down the predictive value of a positive test result, even if the test itself is quite good.
However, when the same patient attends a specialist clinic at the hospital, where a lot of selection has already taken place and a larger proportion of all the patients have the disease, the predictive value of the same test will be much higher. This was well illustrated in the BMJ article mentioned earlier.
More on sensitivity, prevalence and predictive values Conclusion: This introduces likelihood ratios.