Laboratory tests in the diagnosis of pulmonary embolism

The diagnosis of pulmonary embolism (PE) requires objective testing. However, all imaging techniques have their own limitations and costs and cannot be performed in every patient with suspected PE. After decades of unfruitful research, several laboratory tests have been evaluated for suspected PE, the most promising being the D-dimer test. As a general rule, the specificity of D-dimers is too low to confirm PE. Conversely, several (but not all) D-dimer assays have a high sensitivity for diagnosing PE. Outcome studies indicate that the Vidas D-dimer and SimpliRED D-dimer can be used safely to withdraw anticoagulation when the pretest probability of PE is low (SimpliRED) or when it is low or moderate (Vidas). These results may however not apply to other D-dimer assays and clinicians should know the characteristics of the test used in their hospital. Blood gas analysis does not have sufficient sensitivity and specificity to confirm or exclude PE, but it may be used to evaluate the clinical probability of PE before other testing is done. The diagnostic value of the alveolar dead space fraction in patients with suspected PE is currently investigated. Initial data suggest that it needs to be combined with a D-dimer test to safely exclude PE. Brain natriuretic peptide and cardiac troponin have limited usefulness for diagnosing PE, but both tests may identify patients with a poor prognosis, in whom more aggressive treatment may be warranted.     

Breath tests in the diagnosis of gastrointestinal diseases

Determination of carbon or hydrogen markers in breath has allowed closer investigation of the pathogenic mechanisms of several gastrointestinal diseases. Thus, the 13C-urea breath test is a nonaggressive, simple and safe test with excellent accuracy both in the initial diagnosis of Helicobacter pylori infection and in confirmation of its eradication following treatment. Moreover, because of the simplicity, reproducibility and safety of these types of procedure, they have tended to substitute more uncomfortable and expensive techniques that were traditionally used in gastroenterology. Several breath tests have been developed that allow reliable evaluation of liver or exocrine pancreatic function, gastrointestinal motility, as related to gastric emptying or orocecal transit time, and a diagnostic approach to clinical problems that could be due to bacterial overgrowth or malabsorption of various sugars.