The cutoffs of ferritin that have at least 95% PPV or at least 95% NPV to predict reduced iron stores with different preprobabilities. The area below blue line has >95% certainty of reduced iron stores, the area above red line has >95% certainty of full iron stores, and the area between blue and red areas does not have either. The shaded blue and red areas resemble the 95% CI for the cutoffs. Ferritin is in logarithmic scale. The same results in linear scale are presented in supplemental Figure 2. If the preprobability is estimated for a patient, the cutoffs for ruling in iron deficiency can be seen from the figure. For example, for an imaginary patient with 50% preprobability for reduced iron stores, the highest cutoff for ferritin with 95% PPV is 30 μg/L (females) or 51 μg/L (males), and the lowest cutoff with NPV of at least 95% is 1750 or 4967 μg/L, respectively. This means that if the clinician estimates that a patient has a 50% chance of having reduced iron stores, a ferritin level of <30 μg/L (females) or 51 μg/L (males), indicates at least a 95% chance of having reduced iron stores. However, in the same scenario, only a ferritin level of >1750 or 4967 μg/L, respectively, can rule out reduced iron stores with 95% probability.