The white blood count is usually elevated with a left shift in bacterial pneumonia, especially early in the illness. 35 Typically, viral, chlamydial, and pertussis pneumonias produce lymphocytosis. However, it is not unusual for viral pneumonia to initially provoke a significant polymorphonuclear cell response. In patients with mycoplasmal pneumonia, the total white blood count and differential count are usually normal, but the erythrocyte sedimentation rate may be elevated. Chlamydial infections or parasitic infections often produce eosinophilia.
Blood culture results are rarely (5 to 10 percent) positive in children with pneumonia, even when it is proven to be bacterial. 4822 Blood cultures should be obtained in infants who have high fever, appear ill, or require hospitalization. Sputum cultures may also help in identifying the causative organism but are difficult to obtain from nontracheostomized children, particularly those less than 8 years of age.
Cultures of the nasopharynx and throat for viral pathogens, chlamydia, pertussis, and mycoplasma often reveal the causative agent in patients with pneumonia caused by these organisms. Bacterial cultures of these regions have no diagnostic value. 6 Fluorescent antibody tests for C. trachomatis and B. pertussis are preferable to culture in some settings. Rapid viral antigen tests exist for a number of organisms, including RSV and influenza. Bacterial antigen testing is available in some centers but has a poor sensitivity and specificity in diagnosing the cause of pneumonia.423 Serologic testing can be done for viruses, mycoplasma, parasites, and fungi in persistent or puzzling cases. Skin testing for tuberculosis should also be considered in patients not responding to traditional therapy or with apical, cavitary pneumonia. More invasive diagnostic procedures, such as obtaining endotracheal cultures, percutaneous lung aspiration, bronchoalveolar lavage, or open-lung biopsy, may be necessary in patients with severe disease that is unresponsive to empiric therapy. Results of tests for cold agglutinins are positive in 72 to 92 percent of patients with M. pneumoniae infection. Cold agglutinin test results may also be positive in viral infections and are less consistently positive in young children. To perform the bedside test for cold agglutinins, place several drops of blood in a blue-stopper coagulation profile tube, and place it in ice-water for 15 to 30 s. The presence of floccular agglutination is considered a positive result, and agglutination should disappear with rewarming.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.