State which group has the greatest range of blood hepcidin concentration.

Calculate the difference in median blood hepcidin concentration for CHF patients with anemia and without anemia, giving the units.

Using the data, deduce whether the incidence of CHF or the incidence of anemia has a greater effect on the blood hepcidin concentration.

Iron is necessary for hemoglobin to carry oxygen so low iron levels cause low levels of hemoglobin. Suggest reasons for the levels of hepcidin found in CHF patients with anemia.

CHF without anemia

9 ng cm^–3 (calculation not required, accept answers in the range of 8.5 ng cm^–3 to 9.2 ng cm^–3)

median of CHF without anemia greater than median of CHF with anemia;
median of CHF without anemia similar to median of control;
median of CHF with anemia lower than median of control;
anemia (with CHF) appears to be more significant than CHF (without anemia) in affecting hepcidin concentrations;
difficult to determine as overlaps of ranges/population sizes not given/no control with anemia;

low hepcidin levels in CHF patients with anemia;
low hepcidin allows more iron intake/absorption;
more iron allows more hemoglobin so less anemia / low iron leads to anemia;
low iron levels exert negative feedback on hepcidin production;

It seems that this question was extremely difficult for many students. In part (a) the majority read the graph as "without anemia" being the group with the greatest range of hepcidin concentrations, but only a part of them added "CHF patients" to gain the mark, since the control group was also without anemia.

Most calculated the difference correctly for part (b), but a certain number of answers were out of acceptable range, probably due to a too imprecise reading of values.

For part (c), only a part of candidates gained their only mark for deducing that anemia with CHF was more significant in affecting hepcidin concentration; many failed to consider medians when comparing the data, in spite of the focus on the median of the part (b), and many also only compared differences in values without stating if it was higher or lower than the control median value. Some candidates nevertheless noticed how the ranges overlapped and that the data could therefore not be completely trusted.

For part (d), candidates could say that the CHF patients with anemia had lower hepcidin levels, but they often misunderstood the mechanism of why that was true and did not seem to understand that iron could be obtained from nutrition and could be absorbed when hepcidin levels were low to restore iron deficiencies and low hemoglobin. Many stated that the iron was coming from the breakdown of hemoglobin in anemic patients.