Computed and subjective blue scleral color analysis as a diagnostic tool for iron deficiency. Introduction : Iron deficiency (ID) is common in primary care and its diagnosis requires measurement using ferritin due to its non-specific clinical presentation. Blue sclera is described as a specific and sensitive sign of ID but there are few reports of this in the literature. We aimed to determine the diagnostic value of blue sclera for the diagnosis of ID. Methods : We enrolled a total of 74 patients suspected of having ID in a tertiary medical center. Pictures of their eyes were taken using a smartphone under similar daylight. Three independent physicians who were blinded from iron stores, graded the scleral color in anonymized pictures. A computer analysis of the picture yielded the blue percentile (BP) of the sclera. ID was defined where ferritin ≤ 30 μg/L (100 μg/L in case of inflammatory syndrome). Results : Final analysis included 67 patients (mean age 59.9 ± 20.1-year) with a male:female ratio of 0.8. Fifty-one patients had ID. Subjective blue scleral color was associated with ID for physician 1 (p = 0.03) with low sensitivity 60.8% [CI95: 46.1;74.2], specificity 68.8% [CI95: 41.3;89%] and high positive predictive value 86.1% [CI95: 70.5;95.3]. A non-significant trend was observed for other physicians (p = 0.05). Inter-rater reliability was poor (Fleiss’s κ 0.02-0.23). Computer analysis of the pictures showed higher BP in the ID group (p = 0.04). The area-under-the-curve of receiver-operating-characteristics curve was 0.7 [CI95: 0.54;0.85]. Sensitivity was 78.4% [CI95: 63.7;88.7], specificity was 50% [CI95: 24.7;75.3] with a threshold of 29.1. Assessment of blue sclera was not influenced by iris color, sex or anemia. Conclusion : Clinical assessment of blue sclera has good positive-predictive value for ID diagnosis. Computer analysis showed encouraging results correlated to clinical assessment. Improvement of this innovative method could provide simple diagnostic tool for ID diagnosis in primary care.