From: Laboratory Evaluation in the Diagnosis of Lyme Disease
Ann Intern Med. 1997;127(12):1109-1123. doi:10.7326/0003-4819-127-12-199712150-00011
Figure Legend:
Rates of Lyme disease cases in the United States in 1993 as reported by states to the Centers for Disease Control and Prevention.[28]Shown by endemic county. Counties with rates less than 5 per 100 000 or with fewer
than five cases reported are not highlighted. Rates in highly endemic counties ranged from 30 per 100 000 to more than 400 per 100 000 .
Date of download: 7/12/2017
Copyright © American College of Physicians. All rights reserved.
From: Laboratory Evaluation in the Diagnosis of Lyme Disease
Ann Intern Med. 1997;127(12):1109-1123. doi:10.7326/0003-4819-127-12-199712150-00011
Figure Legend:
Scenario A: utility of enzyme-linked immunosorbent assay (ELISA) in patients with nonspecific myalgia.leftrightA nomogram is used to calculate the post-test probability from the pretest probability as follows. The
nomogram expresses probability as a percentage, as modified from the method of Sackett and colleagues. For a patient with an 0.001 pretest probability of Lyme disease, the straight edge was anchored at 0.001 on the
pretest column of the nomogram. Because the likelihood ratio (represented by the center line) for a positive ELISA result was 5.0 ( ), the straight edge was directed through the central column at 5. The post-test probability
was then read as 0.004 from the post-test column of the nomogram. The post-test probability can also be calculated for pretest probabilities of 0.01 and 0.03. For a probability of 0.0001, the post-test probability cannot be
calculated from this nomogram. For a patient with an 0.01 pretest probability of Lyme disease, the straight edge was anchored at 0.01 on the pretest column of the nomogram. Because the likelihood ratio for a positive
ELISA result was 5.0, the straight edge was directed through the central column at 5. The post-test probability was then read as 0.04 from the post-test column of the nomogram. For a patient with an 0.03 pretest
probability of Lyme disease, the straight edge was anchored at 0.03 on the pretest column of the nomogram. Because the likelihood ratio for a positive ELISA result was 5.0, the straight edge was directed through the
central column at 5. The post-test probability was then read as 0.13 from the post-test column of the nomogram. For a negative ELISA result, the likelihood ratio is 0.06 ( ). The procedure is the same as that for a positive
result. For a patient with an 0.03 pretest probability of Lyme disease, the straight edge was anchored at 0.03 on the pretest column of the nomogram and the straight edge was directed through the central column at 0.06.
The post-test probability was then read as 0.0015. The 0.01 (moderate) and 0.001 (low) pretest probabilities reduce to less than 1 in 1000; these probabilities are so low that it is not important to have a precise estimate.
Date of download: 7/12/2017
Copyright © American College of Physicians. All rights reserved.
From: Laboratory Evaluation in the Diagnosis of Lyme Disease
Ann Intern Med. 1997;127(12):1109-1123. doi:10.7326/0003-4819-127-12-199712150-00011
Figure Legend:
Scenario B: utility of enzyme-linked immunosorbent assay (ELISA) in patients with possible erythema migrans.A nomogram is used to calculate the post-test probability from the pretest probability as follows. The
nomogram expresses probability as a percentage, as modified from the method of Sackett and colleagues. For a patient with an 0.80 pretest probability of Lyme disease, the straight edge was anchored at 0.80 on the
pretest column of the nomogram. Because the likelihood ratio (represented by the center line) for a positive ELISA result was 0.80, the straight edge was directed through the central column at 8. The post-test probability
was then read as 0.98 from the post-test column of the nomogram. Conversely, because the likelihood ratio for a negative ELISA result was 0.44, the post-test probability was read as 0.63.
Date of download: 7/12/2017
Copyright © American College of Physicians. All rights reserved.
From: Laboratory Evaluation in the Diagnosis of Lyme Disease
Ann Intern Med. 1997;127(12):1109-1123. doi:10.7326/0003-4819-127-12-199712150-00011
Figure Legend:
Scenario C: utility of enzyme-linked immunosorbent assay (ELISA) in patients who have arthritis and a 0.50 pretest probability of Lyme disease. A nomogram is used to calculate the post-test probability from the pretest
probability as follows. The nomogram expresses probability as a percentage, as modified from the method of Sackett and colleagues. The likelihood ratio (represented by the center line) was approximately 1000 for the
clinical signs and symptoms present in the patient in scenario C. If the cutoff for a positive ELISA result is increased to at least 3 SDs above controls, the likelihood ratio increases to 19.5 and the post-test probability can
then be read as 0.95. For a patient with an 0.50 pretest probability of Lyme disease, the straight edge was anchored at 0.50 on the pretest column of the nomogram. Because the likelihood ratio for a positive ELISA result
was 5.0, the straight edge was directed through the central column at 5. The post-test probability was read as 0.83 from the post-test column of the nomogram. Conversely, because the likelihood ratio for a negative
ELISA result was 0.06, the post-test probability was read as 0.06.
Date of download: 7/12/2017
Copyright © American College of Physicians. All rights reserved.
From: Laboratory Evaluation in the Diagnosis of Lyme Disease
Ann Intern Med. 1997;127(12):1109-1123. doi:10.7326/0003-4819-127-12-199712150-00011
Figure Legend:
Utility of the Western blot for indeterminate enzyme-linked immunosorbent assay (ELISA) results.A nomogram is used to calculate the post-test probability from the pretest probability as follows. The nomogram
expresses probability as a percentage, as modified from the method of Sackett and colleagues. For a patient with an 0.50 pretest probability of Lyme disease, the straight edge was anchored at 0.50 on the pretest column
of the nomogram. Because the likelihood ratio (represented by the center line) for a positive ELISA result was 0.20, the straight edge was directed through the central column at 0.20. The post-test probability was then
read as 0.95. If the ELISA result is indeterminant, the likelihood ratio is 1.05 and the post-test probability is 0.51. If 0.51 is now the pretest probability and Western blot has a positive result, the likelihood ratio is 11.7. This
yields a post-test probability of 0.92.
Date of download: 7/12/2017
Copyright © American College of Physicians. All rights reserved.