Background: Iron deficiency anemia is one of a major problem in children especially in the middle-to-low-income countries. This condition could affect growth and development, so screening anemia at 9-12 months of age in high-risk children is recommended. Non-invasive measurement of hemoglobin saturation (SpHb) by using pulse CO-oximeter may be an alternative method for screening anemia. The optimal site of measurement in children is uncertain.
Objectives: To evaluate correlation coefficient, bias and limits of agreement at group and individual level between non-invasive Hb measurement from various fingers and toes and venous hemoglobin (VHb).
Methods: a prospective diagnostic study was conducted in Chiang Mai University Hospital, Thailand during July 2019 and June 2021. At high risk follow up clinic, 6-24 months of age infants, having a history of preterm birth with gestational age < 34 weeks were included. After inform consent was obtained, hemoglobin saturation (SpHb) was determined by placing cutaneous probe to right fingers and toes. Venous hemoglobin (VHb) was measured from venous blood sampling within 2 hr after non-invasive Hb measurement. Correlation coefficient and the Bland-Altman plot were determined between 2 measurements.
Results: Of 10 patients, mean(SD) chronological age and adjusted age were 14(5.7) months and 12(5.4) months, respectively. At group level, paired t-tests did not show significant differences between SpHb and VHb, except those from the second, forth, and fifth finger. For percent differences, SpHb and VHb from the first finger and all toes had less than 10% difference, interpreting as a good outcome. The Bland-Altman plots showed unbiased , while the first two fingers and toes demonstrated narrower limits of agreement than others. At individual level, SpHb from the first two fingers and toes had shown fair to moderate correlation (r=0.3-0.5). None of fingers or toes showed poor outcome according to cross classification. From perfusion index bar chart, best perfusion index is third finger while forth and first finger are inferior, respectively.
Conclusions: A non-invasive Hb measurement from fingers and toes had fair to moderate correlation with VHb. The first finger might be the optimal site for SpHb measurement because of its satisfied correlation with VHb, narrowed limits of agreement, and acceptable percent mean difference.
Keywords: screening anemia, non-invasive hemoglobin measurement, hemoglobin saturation, venous hemoglobin, the first finger
