A Hampton hump in a<unk> rson with a right lower lobe<unk>  To diagnose a<unk> , a review of clinical criteria to determine the need for testing is recommended. In those who have low risk, age less than 50, heart rate less than 100 beats<unk> r minute, oxygen level more than 94% on room air, and no leg swelling, coughing up of blood, surgery or trauma in the last four weeks, previous blood clots, or estrogen use, further testing is not typically needed. In situations with more high risk individuals, further testing is needed. A CT<unk>  angiogram (CTPA) is the preferred method for diagnosis of a<unk>  due to its easy administration and accuracy. Although a CTPA is preferred, there are also other tests that can be done. For example, a proximal lower limb compression ultrasound (CUS) can be used. This is a test which is primarily used as a confirmatory test, meaning it confirms a previous analysis showing the presence or suspected presence of a<unk> . According to a cross-sectional study, CUS tests have a sensitivity of 41% and specificity of 96%. If there are concerns this is followed by testing to determine a likelihood of being able to confirm a diagnosis by imaging, followed by imaging if other tests have shown that there is a likelihood of a<unk>  diagnosis. The diagnosis of<unk>  is based primarily on validated clinical criteria combined with selective testing because the typical clinical presentation (shortness of breath, chest pain) cannot be definitively differentiated from other causes of chest pain and shortness of breath. The decision to<unk> rform medical imaging is based on clinical reasoning, that is, the medical history, symptoms, and findings on physical examination, followed by an assessment of clinical probability. Probability testing The most commonly used method to predict clinical probability, the Wells score, is a clinical prediction rule, whose use is complicated by multiple versions being available. In 1995, Philip Steven Wells, initially developed a prediction rule (based on a literature search) to predict the likelihood of<unk> , based on clinical criteria. The prediction rule was revised in 1998 This prediction rule was further revised when simplified during a validation by Wells et al. in 2000. In the 2000 publication, Wells proposed two different scoring systems using cutoffs of 2 or 4 with the same prediction rule. In 2001, Wells published results using the more conservative cutoff of 2 to create three categories. An additional version, the "modified extended version", using the more recent cutoff of 2 but including findings from Wells's initial studies were proposed. Most recently, a further study reverted to Wells's earlier use of a cutoff of 4 points to create only two categories. There are additional prediction rules for<unk> , such as the Geneva rule. More importantly, the use of any rule is associated with reduction in recurrent thromboembolism. The Wells score: * clinically suspected DVT – 3.0 points * alternative diagnosis is less likely than<unk>  – 3.0 points * tachycardia (heart rate > 100) – 1.5 points * immobilization (≥ 3d)/surgery in previous four weeks – 1.5 points * history of DVT or<unk>  – 1.5 points * hemoptysis – 1.0 points * malignancy (with treatment within six months) or palliative – 1.0 points Traditional interpretation * Score >6.0 – High (probability 59% based on pooled data) * Score 2.0 to 6.0 – Moderate (probability 29% based on pooled data) * Score 4 –<unk>  likely. Consider diagnostic imaging. * Score 4 or less –<unk>  unlikely. Consider D-dimer to rule out<unk> . Recommendations for a diagnostic algorithm were published by the PIOPED investigators; however, these recommendations do not reflect research using 64 slice MDCT. These investigators recommended: * Low clinical probability. If negative D-dimer,<unk>  is excluded. If positive D-dimer, obtain MDCT and base treatment on results. * Moderate clinical probability. If negative D-dimer,<unk>  is excluded. However, the authors were not concerned that a negative MDCT with negative D-dimer in this setting has a 5% probability of being false. Presumably, the 5% error rate will fall as 64 slice MDCT is more commonly used. If positive D-dimer, obtain MDCT and base treatment on results. * High clinical probability. Proceed to MDCT. If positive, treat, if negative, more tests are needed to exclude<unk> . A D-dimer of less than 750 ug/L does not rule out<unk>  in those who are at high risk.<unk>  rule-out criteria The<unk>  rule-out criteria <unk> RC) helps assess<unk> ople in whom<unk>  is suspected, but unlikely. Unlike the Wells score and Geneva score, which are clinical prediction rules intended to risk stratify<unk> ople with suspected<unk> , the<unk> RC rule is designed to rule out the risk of<unk>  in<unk> ople when the physician has already stratified them into a low-risk category.<unk> ople in this low risk category without any of these criteria may undergo no further testing for<unk> : low oxygen saturations – SaO2 50, hormone use, fast heart rate. The rationale behind this decision is that further testing (specifically CT angiogram of the chest) may cause more harm (from radiation exposure and contrast dye) than the risk of<unk> . The<unk> RC rule has a sensitivity of 97.4% and specificity of 21.9% with a false negative rate of 1.0% (16/1666). Blood tests In<unk> ople with a low or moderate suspicion of<unk> , a normal D-dimer level (shown in a blood test) is enough to exclude the possibility of thrombotic<unk> , with a three-month risk of thromboembolic events being 0.14%. D-dimer is highly sensitive but not specific (specificity around 50%). In other words, a positive D-dimer is not synonymous with<unk> , but a negative D-dimer is, with a good degree of certainty, an indication of absence of a<unk> . A low pretest probability is also valuable in ruling out<unk> . The typical cut off is 500 μg/L, although this varies based on the assay. However, in those over the age of 50, changing the cut-off value to the<unk> rson's age multiplied by 10 μg/L (accounting for assay which has been used) is recommended as it decreases the number of falsely positive tests without missing any additional cases of<unk> . When a<unk>  is being suspected, several blood tests are done in order to exclude important secondary causes of<unk> . This includes a full blood count, clotting status (PT, aPTT, TT), and some screening tests (erythrocyte sedimentation rate, kidney function, liver enzymes, electrolytes). If one of these is abnormal, further investigations might be warranted to the issue. Troponin levels are increased in between 16 and 47% with<unk> . Imaging In typical<unk> ople who are not known to be at high risk of<unk> , imaging is helpful to confirm or exclude a diagnosis of<unk>  after simpler first-line tests are used. Medical societies recommend tests such as the D-dimer to first provide supporting evidence for the need for imaging, and imaging would be done if other tests confirmed a moderate or high probability of finding evidence to support a diagnosis of<unk> . CT<unk>  angiography is the recommended first line diagnostic imaging test in most<unk> ople. Ultrasound of the legs can confirm the presence of a<unk>  but cannot rule it out. CT<unk>  angiography CT<unk>  angiography (CTPA) is a<unk>  angiogram obtained using computed tomography (CT) with radiocontrast rather than right heart catheterization. Its advantages are that it is accurate, it is non-invasive, it is more often available, and it may identifying other lung disorders in case there is no<unk> . The accuracy and non-invasive nature of CTPA also make it advantageous for<unk> ople who are pregnant. File:Computed tomograph of<unk>  vessels.On CT scan,<unk>  emboli can be classified according to the level along the arterial tree. File:SegandSubsegPE.Segmental and subsegmental<unk>  emboli on both sides File:Pulmonary<unk>  CTPA.CT<unk>  angiography showing a "saddle embolus" at the bifurcation of the main<unk>  artery and thrombus burden in the lobar arteries on both sides. File:CT of lung infarction with reverse halo sign, annotated.Pulmonary<unk>  (white arrow) that has been long-standing and has caused a lung infarction (black arrow) seen as a reverse halo sign. Assessing the accuracy of CT<unk>  angiography is hindered by the rapid changes in the number of rows of detectors available in multidetector CT (MDCT) machines. According to a cohort study, single-slice spiral CT may help diagnose detection among<unk> ople with suspected<unk> . In this study, the sensitivity was 69% and specificity was 84%. In this study which had a prevalence of detection was 32%, the positive predictive value of 67.0% and negative predictive value of 85.2%. However, this study's results may be biased due to possible incorporation bias, since the CT scan was the final diagnostic tool in<unk> ople with<unk> . The authors noted that a negative single slice CT scan is insufficient to rule out<unk>  on its own. A separate study with a mixture of 4 slice and 16 slice scanners reported a sensitivity of 83% and a specificity of
Pulmonary embolism
Dilated cardiomyopathy
Pulmonary hemorrhage
Pneumonia
Pleural effusion
Costochondritis
Lung infarction
Myocardial stunning