Table 5.

Expected changes to iron parameters throughout the menstrual cycle in active females.

Commonly measured iron variable	What does it measure	Early Follicular Phase: Menses	Mid to late Follicular phase	Luteal phase	Factors that will upregulate iron parameters	Factors that will downregulate iron parameters
Serum Iron	Measure of how much iron is in your plasma	Low	Low/ Gradual increase	High	Previous exercise session, exogenous/synthetic estrogens, iron supplements, diurnal variation (afternoon), dietary intake	Menstrual bleeding, diurnal variation (morning), dietary intake, inflammation, E2
Total iron binding capacity (TIBC)	Measure of the blood capacity to bind with iron	High	High	Low	Menstrual bleeding, dietary intake, serum iron, basal iron status	Dietary intake, serum iron, basal iron status
Transferrin Saturation	Measure of a percentage of iron bound to transferrin. Calculated as Serum iron/TIBC	Low	Low/ Gradual increase	High Early luteal phase it is not uncommon for females to present with > 45%	Mirrors changes in serum iron	Mirrors changes in serum iron
Hemoglobin	Measure of free levels of hemoglobin in the blood	Low/ Normal	Increasing/No change	High/ No change	Previous exercise, dehydration, decrease in plasma volume (e.g., post exercise shifts, changes with posture)	Haemodilution, hypovolemia with training or heat adaptation, increase fluid retention due to P4 in luteal phase,
Serum Ferritin	Measure of the body's iron stores	Low/ no change	Increasing/no change	High/no change	Previous exercise, infection/illness, inflammation, iron infusion/injection, prolonged suppression of serum hepcidin	Prolonged elevation in serum hepcidin, iron supplements or iron rich food in iron sufficient individuals
Serum Hepcidin	Measure of the concentration of hepcidin in the blood	Low/No change	Increasing/No change	High/No change	Previous exercise, dehydration, decrease in plasma volume, P4, energy availability status, inflammation/illness/ infection, iron supplements, iron fortified foods, high-normal iron status	Haemodilution, hypovolemia, hydration status, E2, carbohydrate availability, altitude exposure, enhanced erythropoiesis, deficient iron status