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Centre for Evidence-
Based Medicine

Completed Diagnosis Worksheet for Evidence-Based Gastroenterology and Hepatology

Citation

Guyatt GH, Patterson C, Ali M, Singer J, Levine M, Turpie I, Meyer R: Diagnosis of iron-deficiency anemia in the elderly. Am J Med 1990;88:205-9.

Are the results of this diagnostic study valid?

  1. Was there an independent, blind comparison with a reference ("gold") standard of diagnosis?
    Yes, they underwent bone-marrow aspirations.
  2. Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom it would be used in practice)?
    Yes
  3. Was the reference standard applied regardless of the diagnostic test result?
    Yes

Are the valid results of this diagnostic study important?

Ferritin Iron Deficiency No Iron Deficiency Likelihood Ratio
≤ 45 70/85 15/150 8.2
> 45 ≤ 100 7/85 27/150 0.44
> 100 8/85 108/150 0.13
Totals 85 150
  • For pre-test probabilities in the 30-70% range, a ferritin < 45 would be very helpful, yielding post-test probabilities of 78-95% (in the latter case, a SpPin1).
  • In that same pre-test probability range, a ferritin > 100 would yield post-test probabilities of 5-23% (in the former case, a SnNout2).
  • So it can give quite important results.

Notes

  1. When a diagnostic test has a very high Specificity, a Positive result Rules-In the diagnosis.
  2. When a diagnostic test has a very high Sensitivity, a Negative result Rules-Out the diagnosis.

Can you apply this valid, important evidence about a diagnostic test in caring for your patient?

  1. Is the diagnostic test available, affordable, accurate, and precise in your setting?
    Needs to be assessed in each setting.
  2. Can you generate a clinically sensible estimate of your patient's pre-test probability (from practice data, from personal experience, from the report itself, or from clinical speculation)
    Approximately 30%.
  3. Will the resulting post-test probabilities affect your management and help your patient? (Could it move you across a test-treatment threshold?; Would your patient be a willing partner in carrying it out?)
    Her result of 40 brings her post-test probability to 78%, certainly high enough for you to want to investigate her for causes of anaemia (GI loss, etc.).
  4. Would the consequences of the test help your patient?
    Yes, if it led to a reversible cause. But this would have to be weighed against early detection of an untreatable cause (e.g., cancer) that would simply take away "healthy" time. The options would need to be discussed with your patient.

Additional Notes

An excellent overview of 55 studies of lab tests for Fe-deficient anaemia: Guyatt et al: J Gen Intern Med 1992;7:145-53 (with a correction on page 423).

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