Diagnosis: Clinical Scenario
You admit a well 75 year old woman with community-acquired pneumonia. She responds nicely to appropriate antibiotics but her haemoglobin remains at 100 g/l with a mean cell volume of 80. Her peripheral blood smear shows hypochromia, she is otherwise well, and is on no incriminating medications. You contact her GP and find out that her haemoglobin was 105 g/l 6 months ago. She has never been investigated for anaemia. You discuss this patient with your registrar and debate the use of ferritin in the diagnosis of iron deficiency anaemia. You admit to yourself that you are unsure how to interpret a ferritin result and how precise and accurate a serum ferritin is for diagnosing iron deficiency anaemia.
You therefore form the question, "In an elderly woman with hypochromic, microcytic anaemia, can a low ferritin diagnose iron deficiency anaemia?" You order a ferritin and head for the library (10 days later it comes back at 40 µg/l).
Searching Best Evidence on Disk with the single word "ferritin" yielded a very encouraging meta-analysis of 55 studies and a nice individual study, but your library didn't carry either journal. You perform a MEDLINE search using the MeSH terms "ferritin" and "sensitivity and specificity" and find an article on diagnosing iron deficiency anaemia in the elderly published in a journal that your library does take Am J Med 1990;88:205-9.
Read the article and decide:
- Are the results of this diagnostic article valid?
- Are the valid results of this diagnostic study important?
- Can you apply this valid, important evidence about a diagnostic test in caring for your patient?