Lab investigations
Lab investigations are not always needed, but they are ordered to detect the causing organism, confirm the diagnosis and assess the general condition. They include:
- Complete blood count: White blood cell count is of particular importance. Patients who have infections tend to have an elevated white cell count. If a patient has all signs of infection and a low or normal white cell count, it can mean they are immunocompromised. Differential count of white blood cells can also be of significance in detecting the type of organism. Neutrophils rise in bacterial infections, lymphocytes in viral infections and autoimmune disorders, and eosinophils in parasitic infestations.
- ESR and CRP: These two markers indicate of inflammation and a rise in their titers usually means that active inflammation is present.
- Sputum culture and tests: In some cases of respiratory tract infection if bacteria are suspected. Sputum culture can identify it and its antibiotic susceptibility. Tuberculosis needs special testing and microscopic stains.
- Blood culture: Blood culture is commonly needed in cases with bacterial endocarditis.
- Urine analysis: Urine analysis can identify the presence of a urinary tract infection and the bacteria causing it. Culture can also be done on the bacteria to identify its antibiotic susceptibility.
- Stool analysis and culture: Stool analysis can reveal the presence of parasitic ova and some bacteria. Stool culture can also help identify bacteria and their antibiotic susceptibility.
- Lumbar puncture: Lumbar puncture and CSF analysis are done when meningitis is suspected by clinical symptoms or examination. The CSF will be examined both by eye and under the microscope and any bacteria will be cultured.
- Immunological markers: Immunological markers can be used in case of suspicion of autoimmune diseases like systemic lupus. Commonly ordered serological tests include rheumatoid factor for rheumatoid arthritis, anti-ds DNA and anti-nuclear antibodies for lupus.