It is possible that a person with a history of pneumonia may develop a blood clot in the lungs, according to Physicians' Desk Reference. A blood clot in the lungs can cause a pulmonary embolism, which is a blockage in a lung artery. Although pneumonia may be one cause for this condition, there are many others, including immobility due to illness, heart problems, cancer, surgical procedures, obesity and inherited disorders, states Mayo Clinic.
Some other risk factors for a pulmonary embolism are stroke, pregnancy, injury to the legs and lung disease, relates Physicians' Desk Reference. Some symptoms of pulmonary embolism are pain in the chest area, fast pulse, breathing problems, a cough that produces blood and fainting. These symptoms may require immediate medical attention, reports WebMD.
Pulmonary embolism can be difficult to diagnose because some of its symptoms are similar to other conditions like a heart attack and even pneumonia, informs Physicians' Desk Reference. To rule out pneumonia being the problem, a chest X-ray can be ordered by doctors. Although, a D-dimer blood test may suggest there may be a blood clot in the lungs, a CT scan or a pulmonary angiogram may be needed to make the diagnosis.
A case of pulmonary embolism is especially difficult to diagnose if the person has pneumonia and develops a lung blood clot. In such a case, results of some tests can be uncertain, states Physicians' Desk Reference. For this reason, a battery of tests need to be performed to detect and treat blood clots that lead to pulmonary embolism.