Iron Panel

Iron is one of the few nutrients that is dangerous in both directions. Too little, and your cells starve for oxygen and energy. Too much, and the surplus corrodes your organs from the inside. The two extremes do not announce themselves equally. A low ferritin flags deficiency clearly enough, but excess iron, which the body has no way to excrete, builds for years behind numbers that can still read normal.

That is why iron is ordered as a panel, not a single test. Each test in it photographs a different point in the same supply chain: how much iron is moving through your blood right now, how much your blood could carry, what fraction of that capacity is filled, and how much you have locked away in storage. Any one of those numbers, read alone, can reassure you while the others are sounding an alarm.

The pattern is the whole point. A normal ferritin can sit beside a transport system already loaded past capacity, the early signature of hereditary iron overload. A normal hemoglobin can sit beside stores that emptied months ago. Reading the panel as a pattern is how you tell genuine deficiency from inflammation, and either of those from the slow overload that hides for decades. It is also why this site exists. Read the lab result that started everything →

The panel measures iron at four points, and each one means little without the others.

Serum iron is the iron actually circulating, bound to its transport protein. It is the most volatile number on the panel. It rises after an iron-rich meal or a supplement and follows a daily rhythm, highest in the morning and lower by evening. On its own it is nearly useless, which is why it is never read in isolation.

TIBC (total iron-binding capacity) measures the total amount of iron your transport protein, transferrin, could carry if every site were full. The liver adjusts it deliberately. When iron is scarce, it builds more transferrin, so TIBC rises and more carts go out to find iron. When iron is abundant, it builds less, and TIBC falls ^[1]. Some labs measure the transferrin protein directly instead of TIBC, but the two are interchangeable here, since saturation can be calculated from either. You will rarely see transferrin itself listed on a panel, because TIBC already does its job.

Transferrin saturation is serum iron divided by TIBC, times one hundred: the percentage of the fleet that is loaded ^[2]. That ratio is what makes the number readable: a given serum iron means little until you know the capacity behind it, and saturation builds that context in. It is the panel's single best screen, running low in deficiency and high in overload.

Ferritin is the storehouse. A protein shell that holds iron safely in reserve, and the earliest marker to fall when iron runs short. Its one weakness is that it also rises with inflammation, which is why it is never read without context.

Put together, the four numbers resolve into three patterns. In deficiency, ferritin falls first, then saturation drops while TIBC climbs, and only last does hemoglobin fall ^[3]. In inflammation, the liver hormone hepcidin locks iron inside cells: serum iron and saturation fall while ferritin rises, so the storehouse reads full while the floor runs empty. In overload, saturation climbs first, often past 45%, while ferritin can still read deceptively normal.

Two thresholds do most of the interpretive work.

On the low end, most labs flag ferritin as deficient only below 12 to 15 ng/mL, but the World Health Organization uses 30 ng/mL, the level where the body's iron reserves are genuinely empty. That higher cutoff is anchored to the iron in bone marrow, the most direct measure of iron stores there is ^[4]. Millions of people sit in the gap. Technically normal on paper, functionally depleted, tired for reasons no one connects to iron. A transferrin saturation below 20% alongside a low ferritin confirms the picture.

On the high end, a fasting transferrin saturation above 45% is the established trigger to investigate iron overload ^[5]. This is where the panel earns its place, because saturation tends to rise before ferritin in genetic iron loading ^[6]. The condition is hereditary hemochromatosis, driven mostly by two copies of the HFE C282Y variant, and it is the most common genetic disorder in people of Northern European descent. A screening study of nearly 100,000 people confirmed both how common the genotype is and how badly symptoms alone catch it, since the overload hides for decades behind vague fatigue and joint pain ^[7]. Carrying the genotype does not guarantee disease: iron-overload-related illness developed in roughly 28% of male C282Y homozygotes but only about 1% of women, whose monthly iron losses are protective for much of life ^[8]. The genotype sets the risk; the panel reveals whether it is being expressed.

The reason the high end matters even at "normal-ish" levels is that excess iron is not inert. Once the transport system is overwhelmed, unescorted iron settles into the liver, pancreas, heart, and joints and generates the free radicals that accelerate their aging. A long Danish cohort found mortality rising in a stepwise fashion with ferritin, with median survival falling sharply at the upper end ^[9]. The goal is not simply to avoid anemia. It is to stay in the window where iron is always available and never loose.