Ferritin in single figures while haemoglobin reads normal. That is the pattern we see most weeks in active women referred from a GP visit that came back "all clear". The standard NZ iron panel often anchors to haemoglobin and serum iron, and by the time those flag, the deficit has been running for months. Active women pay the energy bill before the diagnosis arrives.

What the standard GP iron test misses

A typical iron screen in New Zealand returns haemoglobin, haematocrit, MCV, serum iron, transferrin, transferrin saturation, and ferritin. On paper, that looks thorough. In practice, the result usually gets read against haemoglobin first. If haemoglobin sits inside the reference range, the panel is called normal and the conversation stops.

The problem: haemoglobin is the last domino. Iron stores deplete first (low ferritin), then transport iron drops (low transferrin saturation), and only then does red cell production suffer (low haemoglobin). A woman training five to ten hours a week can sit at a ferritin of 12 µg/L with a haemoglobin of 135 g/L and be told she is fine. She is not fine. She is iron deficient without anaemia, and her training, sleep, and cognition will tell the truth before the bloods do.

The second miss is interpretation. The lab reference range for ferritin in NZ often starts at 15 or 20 µg/L. That floor was built from general population data, not from women who run, lift, or cycle. Performance and recovery thresholds sit higher.

Ferritin thresholds that matter for active women

We work alongside your GP on this, but the thresholds we use in coaching context are tighter than the lab flag.

  • Below 30 µg/L: iron deficient for performance purposes, regardless of haemoglobin. Symptoms common.
  • 30 to 50 µg/L: depleted stores. Recovery, mood, and endurance often suffer.
  • 50 to 100 µg/L: working range for most active women.
  • Above 100 µg/L: comfortable, particularly through heavy training blocks or pregnancy planning.

These numbers are not a diagnosis. They are a coaching frame. Several research groups, including work out of the AIS and European sports science labs, have flagged ferritin under 30 to 35 µg/L as the point where iron supplementation produces measurable performance and fatigue improvements in menstruating athletes.

The other markers worth requesting: transferrin saturation (under 20% is a red flag), reticulocyte haemoglobin if available, and CRP. Ferritin is an acute phase reactant, so a recent illness, hard training week, or inflammation will inflate the number and hide a real deficit. Reading ferritin without CRP is reading half the page.

Why active women drain iron faster

Three losses stack up. Menstruation is the largest single driver across a month. Foot-strike haemolysis, where red cells rupture under repeated impact in running and court sports, adds a steady drip. Sweat and gut losses round it out. Hepcidin, the hormone that gates iron absorption, also rises for several hours after hard sessions, which means the post-training meal is a poor absorption window.

Layer on a diet that has shifted toward plant-forward eating, and the maths gets harder. Plant (non-haem) iron absorbs at roughly 2 to 10%. Haem iron from red meat absorbs at 15 to 35%. Across our 2,846-food dataset, the gap between a stated iron value on a label and what a woman actually absorbs is one of the largest hidden errors we correct in coaching.

Low ferritin is not a lab quirk. It is the reason a strong week of training feels like wading through wet sand, and the reason the 6am alarm started winning.

Food first, and what that actually looks like

Food cannot rebuild stores from a deep deficit quickly, but it sets the floor that supplementation builds on. The highest-yield foods on our NZ client plans:

  • Beef, lamb, and venison. Lean cuts, two to four servings a week. NZ red meat remains the densest practical source.
  • Liver or pâté. One serving a fortnight delivers more iron than most weeks of salad.
  • Oysters, mussels, and pāua where available. High haem iron and zinc.
  • Eggs, particularly the yolk, daily.
  • Legumes and tofu, paired with vitamin C (kiwifruit, capsicum, citrus) at the same meal to lift non-haem absorption.
  • Cooking acidic foods in cast iron. Small effect, free.

Two practical blockers worth fixing: tea and coffee with meals can cut non-haem iron absorption by 50 to 70%. Move them to 60 to 90 minutes either side of the meal. Calcium supplements taken with iron-rich meals do the same. Separate them.

When supplementation earns its place

If ferritin is under 30 µg/L with symptoms, food alone will take six to twelve months to climb out, and that is if losses stay flat. Supplementation is usually the right tool, run with your GP.

The current evidence favours alternate-day dosing of elemental iron (often 60 to 100 mg) over daily dosing. Hepcidin spikes after an iron dose and blunts absorption for the next 24 hours. Every-other-day dosing absorbs more total iron with fewer gut side effects. Take it on an empty stomach with vitamin C if tolerated. Recheck bloods at eight to twelve weeks.

Iron infusion is a GP and specialist decision, generally reserved for severe deficiency, intolerance to oral iron, or pregnancy timelines. It is not a shortcut, but it is the right call in specific cases.

What to do this week

  • Book a full iron panel with your GP and ask for ferritin, transferrin saturation, and CRP read together.
  • If ferritin is under 50 µg/L, treat it as a performance issue, not a "watch and wait".
  • Move tea and coffee 90 minutes away from your iron-containing meals.
  • Add two to four servings of NZ red meat or equivalent haem sources weekly, with vitamin C at plant-iron meals.
  • If supplementing, discuss alternate-day dosing with your GP and recheck at eight to twelve weeks.

Iron is one of the cleaner problems to solve in nutrition coaching, but only once it is named. The standard panel, read at face value, will keep an active woman tired for a year. A tighter read of the same bloods changes that in a quarter.