Diagnosing empty iron stores in women: unbound iron binding capacity (UIBC) versus soluble transferrin receptor (sTFR)

Figures & data

Table 1. Study population grouped according to CRP < 5 mg/L and pregnancy.

Characteristic	CRP < 5 mg/L		CRP ≥ 5 mg/L
	Not pregnant	Pregnant	Not pregnant	Pregnant
Group no	1	2	3	4
N	1560	169	426	182
Age, years	19 (12–49)	26 (15–44)	30 (12–49)	26 (17–36)
CRP, mg/L	0.7 (0.1–4.9)	2.9 (0.1–4.9)	8.7 (5–139)	9.7 (5–70)
Ferritin, μg/L	33 (2–611)	22 (3–286)	44 (3–499)	22 (3–195)
Hemoglobin, g/dL	13.5 (8.1–16.7)	12.5 (8.6–16.2)	13.3 (6.2–17.0)	12.5 (8.6–14.7)
UIBC, μmol/L	51.0 (3.6–97.2)	60.1 (29.4–125)	54.5 (24.4–101)	66.7 (23.3–114)
sTFR, mg/L	3.4 (1.1–18.6)	3.1 (1.4–11.7)	3.7 (1.3–28.6)	3.4 (1.3–8.6)

The number of women in each group (N) are given, along with median and range (in parenthesis) of age, CRP, ferritin, hemoglobin, UIBC and sTFR.

Table 2. Area under the receiver operating characteristic (ROC) curve (95% confidence interval) for UIBC and sTFR in the four groups of women described in Table 1.

Group	Test	Ferritin cut-off value for empty iron stores
		< 10 µg/L	< 15 µg/L	< 20 µg/L
1: CRP < 5 mg/L, not pregnant	UIBC	0.918 (0.899–0.936)	0.868 (0.844–0.892)	0.830 (0.806–0.854)
	sTFR	0.893 (0.868–0.919)	0.845 (0.819–0.872)	0.793 (0.767–0.819)
2: CRP < 5 mg/L, pregnant	UIBC	0.860 (0.804–0.917)	0.851 (0.793–0.909)	0.843 (0.786–0.901)
	sTFR	0.856 (0.790–0.922)	0.796 (0.723–0.870)	0.739 (0.664–0.814)
3: CRP ≥ 5 mg/L, not pregnant	UIBC	0.904 (0.837–0.971)	0.866 (0.810–0.922)	0.802 (0.747–0.857)
	sTFR	0.921 (0.873–0.970)	0.885 (0.827–0.942)	0.785 (0.723–0.846)
4: CRP ≥ 5 mg/L, pregnant	UIBC	0.843 (0.785–0.901)	0.824 (0.763–0.885)	0.789 (0.723–0.855)
	sTFR	0.771 (0.685–0.857)	0.788 (0.720–0.856)	0.747 (0.677–0.817)

Table 3. Area under the receiver operating characteristic (ROC) curve (95% confidence interval) for various test in diagnosing empty iron stores in 1560 nonpregnant women with CRP < 5 mg/L (group no 1 in Table 1).

Test	Ferritin cut-off value for empty iron stores
	< 10 µg/L	< 15 µg/L	< 20 µg/L
UIBC	0.918 (0.899–0.936)	0.868 (0.844–0.892)	0.830 (0.806–0.854)
sTFR	0.893 (0.868–0.919)	0.845 (0.819–0.872)	0.793 (0.767–0.819)
Iron	0.823 (0.784–0.862)	0.764 (0.729–0.799)	0.724 (0.694–0.754)
TIBC	0.869 (0.842–0.896)	0.831 (0.805–0.857)	0.795 (0.770–0.820)
Transferrin saturation	0.872 (0.841–0.902)	0.814 (0.784–0.845)	0.775 (0.748–0.802)
MCV	0.788 (0.748–0.828)	0.725 (0.689–0.761)	0.694 (0.664–0.725)
MCH	0.809 (0.772–0.846)	0.752 (0.719–0.786)	0.711 (0.681–0.741)
RDW	0.869 (0.838–0.899)	0.821 (0.793–0.850)	0.773 (0.746–0.800)