Skip to main content

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).