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Table 4 Diagnostic performance of ZPP, measured in whole blood or erythrocytes, in detecting iron deficiency a at hypothetical prevalence values (50%, 30%, and 10%) for iron deficiency b

From: Diagnostic utility of zinc protoporphyrin to detect iron deficiency in Kenyan pregnant women

Cut-point

Sensitivity

Specificity

True prevalence

PPV

NPV

Estimated prevalence

Whole blood ZPP, μmol/mol haem

>70c

78%

47%

50%

59%

68%

66%

30%

39%

83%

61%

10%

14%

95%

56%

>49d

95%

3.2%

50%

50%

39%

96%

30%

30%

60%

96%

10%

10%

85%

97%

>85e

63%

63%

50%

63%

63%

50%

>102e

43%

76%

30%

43%

76%

30%

>160e

13%

90%

10%

13%

90%

10%

Erythrocyte ZPP, μmol/mol haem

>70f

38%

87%

50%

75%

58%

26%

30%

56%

77%

21%

10%

25%

93%

16%

>40g

64%

68%

50%

66%

65%

48%

30%

46%

81%

42%

10%

18%

94%

35%

>11h

95%

19%

50%

54%

80%

88%

30%

34%

90%

85%

10%

12%

97%

82%

>34i

67%

67%

50%

67%

67%

50%

>52i

48%

77%

30%

48%

77%

30%

>81i

27%

92%

10%

27%

92%

10%

  1. PPV, Positive predictive value; NA, Not applicable; NPV, Negative predictive value.
  2. aDefined as serum ferritin concentration <15 μg/L; bAnalysis restricted to women without inflammation, Plasmodium infection or HIV infection; cCut-off point corresponding to 2.7 μg/g, which has been selected to define the presence of iron-deficient erythropoiesis [23]; dCut-off point selected for screening, with a sensitivity of 95%; eCut-off points selected to yield unbiased estimates of the prevalence of iron deficiency (see text); fRecommended range to indicate iron deficiency in the absence of infection [24]; gCut-off point recommended to distinguish between iron deficient erythropoiesis and iron sufficient erythropoiesis [2]; hCut-off point selected for screening, with a sensitivity of 95%; iCut-off points selected to yield unbiased estimates of the prevalence of iron deficiency (see text).