Sunday, July 8, 2012

Color of the Eyes

Motivation: Part of the checklist on the physical exam is looking at patients' eyes and deciding on paleness. I would love to be able to gauge degree of anemia without Q6 blood draws, but are the eyes a good way to decide on degree of anemia?

For background, while looking at the conjunctiva, pallor is determined by comparing the posterior edge of the palpebra (just where it intersects with the conjunctiva) with the anterior edge of the palpebra bordering the eyelashes.  Normally, the anterior edge is redder than the posterior edge.  In anemia, the anterior and posterior edge are the same color.  Pasted below are pictures of a normal and anemia conjunctival exam:

Normal Conjunctiva

Conjunctival Pallor
 Paper: Sheth, T.N., Choudhry, N.K., Bowes, M. et. al. "The Relation of Conjunctival Pallor to the Presence of Anemia." J. Gen. Intern. Med. (1997); 12: 102-106.





















Methods: 302 medical and surgical inpatients at The Toronto Hospital were prospectively assessed for conjunctival pallor (present/borderline/absent) and compared to the patient's hemoglobin.  The observers (medical students and general internists) were initially trained on 25 patients but were blinded to the hemoglobin levels.  While no primary endpoint was stated, the overall goal was the utility of conjunctival pallor in ruling in or ruling out moderate anemia (hemoglogin < 9 g/dL).

Results:
Cohort: Of the 302 patients examined, 171 were male and 131 were female.  55 had hemoglobin less than 9 g/dL while 247 had higher values.

Conjunctival Pallor:  With hemoglobin cutoff of 9 g/dL, the performance of pallor is as below:
- Sensitivity (pallor present):  14.5%
- Sensitivity (pallor present/borderline): 54.5%
- Specificity (pallor absent): 74.4%.


Discussion: In the final analysis, conjunctival pallor is just not a reliable test for anemia even for trained observers.  A definitely positive test only has sensitivity of about 15%.  Even stretching the boundary to positive or borderline positive only yields a sensitivity of about 54%.  So, anemia cannot be ruled out by conjunctival  pallor.  On the other hand, specificity is somewhat higher though 25% of patients with hemoglobin > 9 g/dL remarkably also had conjunctival pallor.  Thus, if pallor is observed, the patient likely has anemia though even that is not a sure thing (in the study, positive likelihood ratio of 4.49)!  I guess CBC are here to stay.

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