Table 3:

Analytic Validity of Baseline Hematologic Biomarkers among Tanzanian pregnant women^1,2

Biomarker		Iron Deficiency (ID)3	Higher cutoff iron deficiency (hID)	Regression-corrected iron deficiency (rID)	Iron deficiency anemia (IDA)	Higher cutoff iron deficiency anemia (hIDA)	Regression-corrected iron deficiency anemia (rIDA)
Hemoglobin, g/L
>110c	Sensitivity	100%	57%	55%
	Specificity	85%	70%	74%
ZPP
>70c	Sensitivity	60%	89%	45%	70%	66%	62%
	Specificity	79%	50%	88%	78%	80%	79%
sTfR, mg/L
>4.4c	Sensitivity	31%	25%	26%	37%	35%	35%
	Specificity	91%	93%	93%	91%	92%	91%
Hepcidin, μg/L
≤13.3c	Sensitivity	99%	100%	100%	100%	100%	100
	Specificity	4%	7%	6%	4%	4%	4%
≤1.6j	Sensitivity	82%	76%	75%	86%	84%	83%
	Specificity	61%	79%	74%	58%	61%	60%

^cCut-off is conventional;

^jCut-off identified using Youden Index;

^*P-value <0.05;

^**P-value<0.01;

^***P-value <0.001

¹All biomarkers tested at baseline.

²Sensitivity was calculated as a/a+c, where a=number of patients meeting both the test biomarker threshold (ZPP or sTfR or Hepcidin) and the comparator threshold (hemoglobin or ferritin or both), and c=number of patients meeting comparator threshold but not the test biomarker threshold. Specificity was calculated as d/b+d, where d=number of patients who did not meet both the test biomarker threshold and the comparator threshold, and b=number of patients meeting the test biomarker threshold but not the comparator threshold. In some cases, a, b, c or d were equal to zero, and these were replaced with 0.5. The Youden index is a summary statistic of the ROC curve and maximizes the sum of the sensitivity and specificity

³Anemia was defined as hemoglobin <110g/L. Iron deficiency was defined as ferritin ≤15 μg/L regardless of inflammation. Higher cutoff iron deficiency was defined depending on the presence (ferritin, <30 μg/L; CRP, >8.2 μg/mL) or absence (ferritin, <15 μg/L; CRP, ≤8.2 μg/mL) of inflammation

Values are percentages.