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FOR POOR PATIENTS D-DIMER BLOOD TEST ENOUGH TO EXCLUDE PULMONARY EMBOLISM
OP KAPOOR
Ex. Hon. Physician, Jaslok Hospital and Bombay Hospital, Mumbai, Ex. Hon. Prof. of Medicine, Grant Medical College and JJ Hospital, Mumbai 400 008.
The diagnosis of venous thrombo-embolism, often cited as pulmonary embolism is difficult to confirm even in rich people. In practice, in a patient with a known background of risk factors, if an attack of one sided chest pain occurs with sudden dyspnoea (more often tachypnoea - very fast respiratory rate), with or without cough, the diagnosis of pulmonary embolism is extremely likely, even if X-ray chest is normal. Now low molecular weight (LMW) heparin is available and can be injected at home without doing any prothrombin time (PT) or INR tests. Such patients can be safely put on 8-10 days course of this drug.
Coming to the investigations, to confirm the diagnosis, even in patients who are affording, there are a lot of problems.
1. If SPO2 can be done by the family physician a low reading would be extremely useful. But, once the blood test for ABG (arterial blood gases) is asked for, the patient has to go to a big hospital to get this costly test done.
2. Regarding the lung scan (to look for a mismatched ventilation perfusion scan), although
i) it is very costly and
ii) is being done only at 2-4 centres even in a big city like Mumbai, the interpretation of the test is very often misguiding-especially in patients, whose chest X-ray is abnormal.
3. Doppler studies of the veins of the legs are not only costly, but also do not exclude other sites like pelvic vein thrombosis, as the cause of pulmonary embolism.
If so, then in a poor patient, in my opinion, the blood test for D-Dimer only may be asked for. Fortunately, it is elevated in 60-70% of the patients, in whom there is absolutely no need to do an ABG study or Lung Scan or Doppler studies, the costs of which run into thousands of rupees.
Yes, it is known that D-Dimer can be elevated if the patient has deep vein thrombosis, even without pulmonary embolism. But in the clinical setting mentioned above, it will be justifiable to put this patient on a course of LMW heparin. Finally, a "negative" D-dimer test helps a good clinician to exclude pulmonary embolism.
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