A total of 148 lung scans were performed on 137 patients over the eight-month study period. Seven patients had more than one lung scan because of repeated episodes, raising the suspicion of pulmonary embolism. Plasma samples were obtained from pa­tients at the time of the lung scans. All but 20 samples were collected within 48 hours of the lung scan. At the time of 17 scans, the patient either refused or was not available for phlebotomy and was excluded from further consideration. Thirty-two patients accounting for 37 lung scans were excluded from analysis for having either conditions other than pulmonary em­bolism that are associated with increased levels of plasma DNA or for having prolonged symptoms. Table 1 summarizes the various conditions leading to exclu­sion.

The remaining 94 episodes of suspected pulmonary embolism were divided into two groups according to the certainty of pulmonary embolism diagnosis. The diagnosis established group consisted of patients in whom the presence or absence of pulmonary embo­lism was established. These patients had either a high probability lung scan, normal lung scan, or pulmonary angiography. The diagnosis uncertain group included patients for whom the diagnosis of pulmonary embo­lism was not definitely established. This group con­sisted of patients with lung scans interpreted as low probability, intermediate probability, or indeterminate lung scan and no pulmonary angiography.
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Table 1—Reasons for Exclusion from the Study

No. of

No. with

Reasons*

Lung Scans

Plasma DNA

Major surgery

Intracranial

1

1

Intrathoracic

1

1

Intra-abdominal

2

2

Orthopedic

5

3

Corticosteroids

9

5

(>40 mg prednisone a day)

Hemodialysis

4

4

SLE with active vasculitis

1

1

Major burn

1

1

Liver failure

1

1

Chemotherapy

1

1

Sickle cell disease with

1

0

vaso-occlusive crisis

Symptoms of PE>7 days

10

4

Plasma not collected

17

Totals

54

24

We considered a pulmonary embolism to be present if a patient had either a high probability lung scan or an abnormal pulmonary angiogram. Pulmonary em­bolism was considered definitely ruled out if the lung scan was normal or the pulmonary angiogram was normal. The angiogram result superceded the lung scan result in conflicting cases.

Table 2—Clinical Characteristics of the Patients in the Three Groups

Diagnosis
Diagnosis Established* Uncertain*}* Excluded^

No. of lung scans

49

45

54

(total
148)

Age, y, mean

53

57

53

Gender, percent
male

53

49

43

Risk factors for
PE,

80

93

78

percent

Prolonged bedrest

29

38

44

Previous
thrombosis

25

24

24

Obesity

16

27

20

Postoperative

25

24

24

Malignant
neoplasm

18

13

17

Symptoms
consistent with

94

87

89

PE, percent

Dyspnea

65

49

67

Pleuritic chest
pain

51

40

39

Nonpruritic chest
pain

29

18

17

Hemoptysis

10

2

6

Nonresponsive
patient

4

11

9

Normal lower
extremities,

63

73

81

percent

Lower extremity
pain or

35

27

13

swelling,
percent§

Pretest
probability,

mean||

46

43

39

In Table 2 we compare various demographic and clinical characteristics of the two diagnostic groups and the excluded group. The only statistically signifi­cant difference among all group comparisons was in the proportion of patients who had findings suggestive of deep venous thrombosis on physical examination of the lower extremity. Within the diagnosis established patient group, the clinical suspicion for pulmonary embolism (pretest probability) was compared for pa­tients with and without a final diagnosis of pulmonary embolism and for patients with and without detectable plasma DNA. Patients who proved to have pulmonary embolism had higher pretest probabilities than those without this final diagnosis (55.6 percent vs 42.6 percent, p= .08 by SAS General Linear Models pro­cedure), and patients with plasma DNA also had higher pretest probabilities than patients without detectable DNA (57.5 percent vs 41.4 percent, p= .03). cheap viagra online