{"id":15096,"date":"2026-10-20T15:00:00","date_gmt":"2026-10-20T15:00:00","guid":{"rendered":"https:\/\/bioprofile.com\/?page_id=15096"},"modified":"2026-11-05T05:39:27","modified_gmt":"2026-11-05T05:39:27","slug":"free-t4","status":"publish","type":"page","link":"https:\/\/bioprofile.com\/en\/biomarkers\/free-t4\/","title":{"rendered":"Free T4"},"content":{"rendered":"\n<div id=\"content\" tabindex=\"-1\"><\/div>\n<style>@import url('https:\/\/fonts.googleapis.com\/css2?family=Poppins:ital,wght@0,400;0,600;0,700;0,800;1,400&display=swap');\n\/* ===========================================================================\n   BioProfile advertorial, the design Jesse approved on 2026-07-30, expressed\n   as a WordPress design system.\n\n   THE @import IS LOAD BEARING and must stay the first thing in this sheet (a\n   CSS @import after any rule is dropped by the parser). elementor_canvas does\n   not enqueue the theme's fonts, so without it the whole page falls back to the\n   system font. Caught by LOOKING at the live page on 2026-07-30, right after\n   the template was switched to canvas.\n\n   Everything is scoped to `.bp-adv`, so nothing here can reach the rest of\n   bioprofile.com, and core blocks are styled BY ELEMENT so a heading, a\n   paragraph, a quote, a list, an image or a button inserted by hand inside the\n   advertorial comes out on-design with no class to remember.\n\n   Jesse's design feedback, 2026-07-29 23:38, point by point:\n   1. the light green and the dark green are the preferred colours; grey may be\n      used but the page must NOT open grey;\n   2. more colour and variation across sections, e.g. a colour block on the left\n      or the right side of a section, without overdesign;\n   3. ONE H1, plain text on white; everything else H2 or H3; an H2 may carry its\n      own background colour so the page can be read from the headings alone; an\n      H3 keeps its section background and gets a bigger font size;\n   4. reuse the results page design feel;\n   5. Written by \/ Verified by, the placeholder blocks and noindex stay.\n\n   COLOUR PROVENANCE. Not one hex is invented.\n   - #b7cb32  LIGHT GREEN, brand manual \"colours rejuvenation protocol\"\n              (R183 G203 B51). Same value as --bp-lime in\n              brands\/bioprofile\/brand\/tokens.md.\n   - #006b62  DARK GREEN, brand manual, nourish the cells (R0 G107 B98).\n   - #005859  brand manual primary teal, the value the brand is built on.\n   - #228a62  brand manual, challenge the body (R34 G138 B98).\n   - #7ca64c  brand manual, calm the mind (R124 G166 B76).\n   - #dbd4cd  brand manual \"additional color\", the warm neutral.\n   - #B7CB3329 is the brand token --bp-lime-soft (light green at 16 percent).\n   - the gradients are the brand token layer's own, copied verbatim.\n\n   SPECIFICITY NOTE. Elementor's global kit emits `.elementor-kit-6 h2` style\n   rules at (0,1,1). Element rules below are written `.bp-adv h2`, also (0,1,1),\n   and win on source order because this sheet is inline in the body while the\n   kit is a <link> in the head. Component rules that MUST NOT lose carry two\n   classes, e.g. `.bp-adv .wp-block-button__link`.\n\n   LAYOUT NOTE. Vertical rhythm uses `margin-block` and never the `margin`\n   shorthand, so the measure rule `.bp-adv-sec > * { margin-inline: auto }` can\n   centre a block without being outranked by its own element rule.\n   =========================================================================== *\/\n\n.bp-adv {\n  --bp-ink: #212527;\n  --bp-teal: #005859;\n  --bp-forest: #006B62;\n  --bp-emerald: #228A62;\n  --bp-olive: #7CA64C;\n  --bp-lime: #B7CB33;\n  --bp-lime-soft: #B7CB3329;\n  --bp-sand: #DBD4CB;\n  --bp-white: #FFFFFF;\n  --bp-foot: #6b6b6b;\n  --bp-grad-dark: linear-gradient(237deg, rgba(0,88,89,0.00) 62.94%, #005859 100%), linear-gradient(90deg, rgba(34,138,98,0.00) 40%, #228A62 100%), #006B62;\n  --bp-grad-lime: linear-gradient(110deg, rgba(183,203,51,0.00) 36.06%, rgba(183,203,51,0.25) 97.65%), #FFFFFF;\n  --bp-font: 'Poppins','Segoe UI',Arial,sans-serif;\n  --bp-fs-h1: 44px; --bp-fs-h2: 31px; --bp-fs-h3: 24px; --bp-fs-pre: 15px;\n  --bp-fs-body: 17px; --bp-fs-small: 14px; --bp-fs-foot: 13px; --bp-fs-btn: 17px;\n  --bp-lh-body: 1.75;\n  --bp-s-1: 4px; --bp-s-2: 8px; --bp-s-3: 12px; --bp-s-4: 16px;\n  --bp-s-5: 24px; --bp-s-6: 32px; --bp-s-7: 44px; --bp-s-8: 72px;\n  --bp-measure: 760px; --bp-side: 40px;\n  --bp-radius-photo: 16px; --bp-radius-btn: 10px; --bp-radius-card: 20px;\n  --bp-shadow: 0 10px 30px rgba(0,88,89,0.10);\n  font-family: var(--bp-font);\n  font-size: var(--bp-fs-body);\n  line-height: var(--bp-lh-body);\n  color: var(--bp-ink);\n  background: var(--bp-white);\n  -webkit-font-smoothing: antialiased;\n}\n.bp-adv, .bp-adv * { box-sizing: border-box; }\n.bp-adv p, .bp-adv li, .bp-adv h1, .bp-adv h2, .bp-adv h3, .bp-adv blockquote,\n.bp-adv a, .bp-adv cite, .bp-adv span { overflow-wrap: break-word; min-width: 0; }\n\n\/* THE TOGGLE. One word in the block's own \"Additional CSS class(es)\" field\n   hides an optional component on the front end without deleting anything. *\/\n.bp-adv .bp-off { display: none !important; }\n\n\/* the page opens on green, never on grey (his point 1) *\/\n.bp-adv .bp-adv-rule {\n  height: 6px; border: 0; margin-block: 0; max-width: none;\n  background: linear-gradient(90deg, #005859 0%, #006B62 38%, #228A62 66%, #B7CB33 100%);\n}\n\n\/* --- section surfaces ------------------------------------------------------ *\/\n.bp-adv-sec { position: relative; background: var(--bp-white);\n  padding: var(--bp-s-8) var(--bp-side); margin-block: 0; }\n\/* the measure: every direct child of a section is the 760px text column *\/\n.bp-adv-sec > * { max-width: var(--bp-measure); margin-inline: auto; }\n.bp-adv-sec > *:last-child { margin-block-end: 0; }\n.bp-adv-sec--wash  { background: linear-gradient(180deg, #B7CB331F 0%, #B7CB3312 100%), #FFFFFF; }\n.bp-adv-sec--dark  { background: var(--bp-grad-dark); color: var(--bp-white); }\n.bp-adv-sec--dark p, .bp-adv-sec--dark cite, .bp-adv-sec--dark li { color: var(--bp-white); }\n.bp-adv-sec--offer { background: var(--bp-grad-lime); text-align: center; }\n.bp-adv-sec--hero  { padding-block-start: var(--bp-s-6); }\n.bp-adv-sec--disclosure { padding-block: var(--bp-s-6);\n  border-top: 1px solid var(--bp-sand); }\n\n\/* --- the side accent bar, his own example (\"a colour block on the left or the\n       right side of a section\"), design rev 3: a slim vertical bar hugging the\n       text column rather than a wide margin panel. Below 1100px the margin is\n       gone, so it becomes a slim top edge. ---------------------------------- *\/\n.bp-adv-rail { overflow: hidden; }\n.bp-adv-rail::before {\n  content: \"\"; position: absolute; top: var(--bp-s-7); bottom: var(--bp-s-7);\n  width: 6px; border-radius: 3px;\n  background: linear-gradient(180deg, var(--bp-forest) 0%, var(--bp-lime) 100%);\n}\n.bp-adv-rail--left::before  { left: calc((100% - var(--bp-measure)) \/ 2 - 34px); }\n.bp-adv-rail--right::before { right: calc((100% - var(--bp-measure)) \/ 2 - 34px); }\n@media (max-width: 1099px) {\n  .bp-adv-rail::before { left: 0; right: 0; width: auto; bottom: auto; top: 0;\n    height: 4px; border-radius: 0; background: var(--bp-lime); }\n}\n\n\/* --- CORE BLOCKS, styled by element. This is the part that makes an inserted\n       block come out on-design with no class. --------------------------------- *\/\n.bp-adv p { font-size: var(--bp-fs-body); line-height: var(--bp-lh-body);\n  margin-block: 0 var(--bp-s-5); }\n.bp-adv h1 { font-size: var(--bp-fs-h1); font-weight: 700; line-height: 1.22;\n  margin-block: 0 var(--bp-s-4); }\n\/* an H2 is its own colour band, so the page can be read from the headings\n   alone (his point 3). Dark green on light sections, light green on the dark\n   one, so a heading always wins against its own background. *\/\n.bp-adv h2 {\n  font-size: var(--bp-fs-h2); font-weight: 700; line-height: 1.28;\n  margin-block: 0 var(--bp-s-5);\n  background: var(--bp-grad-dark); color: var(--bp-white);\n  padding: var(--bp-s-4) var(--bp-s-5);\n  border-radius: var(--bp-radius-btn);\n  border-left: 6px solid var(--bp-lime);\n}\n.bp-adv-sec--dark h2 { background: var(--bp-lime); color: var(--bp-ink);\n  border-left-color: var(--bp-forest); }\n\/* H3: same background as its section, bigger font (his point 3, verbatim) *\/\n.bp-adv h3 { font-size: var(--bp-fs-h3); font-weight: 700; line-height: 1.35;\n  color: var(--bp-forest); background: transparent; margin-block: 0 var(--bp-s-3); }\n.bp-adv-sec--dark h3 { color: var(--bp-lime); }\n.bp-adv ul, .bp-adv ol { font-size: var(--bp-fs-body); line-height: var(--bp-lh-body);\n  margin-block: 0 var(--bp-s-5); padding-left: var(--bp-s-5); }\n.bp-adv li { margin-block-end: var(--bp-s-2); }\n.bp-adv a { color: var(--bp-teal); text-decoration: underline; }\n.bp-adv a:hover { color: var(--bp-olive); }\n.bp-adv-sec--dark a, .bp-adv-sec--dark strong { color: var(--bp-lime); }\n.bp-adv strong { font-weight: 700; }\n\/* the highlight pill. Colours ride on the inline style core writes, so only\n   the shape lives here and any <mark> in the article picks it up. *\/\n.bp-adv mark {\n  padding: 0 10px; border-radius: 10px; display: inline;\n  -webkit-box-decoration-break: clone; box-decoration-break: clone;\n}\n\/* figures match the approved page exactly: card radius plus the soft shadow,\n   and a left-aligned caption rather than core's centred one *\/\n.bp-adv .wp-block-image { margin-block: var(--bp-s-5); margin-inline: auto; }\n.bp-adv .wp-block-image img { display: block; width: 100%; height: auto;\n  border-radius: var(--bp-radius-card); box-shadow: var(--bp-shadow); }\n.bp-adv .wp-block-image figcaption { font-size: var(--bp-fs-foot); line-height: 1.55;\n  color: var(--bp-foot); text-align: left; margin-block: var(--bp-s-2) 0; }\n.bp-adv .wp-block-embed, .bp-adv .wp-block-video { margin-block: var(--bp-s-5); }\n.bp-adv .wp-block-embed iframe, .bp-adv .wp-block-video video {\n  width: 100%; border-radius: var(--bp-radius-photo); }\n.bp-adv .wp-block-separator:not(.bp-adv-rule) { border: 0; border-top: 1px solid var(--bp-sand);\n  margin-block: var(--bp-s-5); }\n\n\/* quotes: core pullquote and core quote both land on the lime rule. The\n   font-size reset undoes core's own 1.5em on the figure, which would otherwise\n   leak into anything inside the quote that has no size of its own. *\/\n\/* margin-inline is load bearing, and it must be `auto` rather than `0`.\n   `blockquote` and `figure` carry a 40px side margin in the browser's own\n   default stylesheet, which indents the quote inside its rule and makes the\n   copy wrap early on a phone. But these blocks are direct children of a\n   section, so zeroing the side margin also defeats the measure rule\n   `.bp-adv-sec > * { margin-inline: auto }` and pins them to the left edge. *\/\n.bp-adv .wp-block-pullquote, .bp-adv .wp-block-quote {\n  border: 0; border-left: 5px solid var(--bp-lime); background: transparent;\n  padding: var(--bp-s-2) 0 var(--bp-s-2) var(--bp-s-5);\n  margin-block: var(--bp-s-5); margin-inline: auto;\n  text-align: left; font-size: var(--bp-fs-body);\n}\n.bp-adv .wp-block-pullquote blockquote { border: 0; margin: 0; padding: 0; }\n.bp-adv .wp-block-pullquote p, .bp-adv .wp-block-quote p {\n  font-size: 24px; line-height: 1.45; font-weight: 600;\n  margin-block: 0 var(--bp-s-2); color: var(--bp-forest); }\n.bp-adv .wp-block-pullquote cite, .bp-adv .wp-block-quote cite {\n  display: block; margin: 0; font-size: var(--bp-fs-small); color: var(--bp-foot);\n  font-style: normal; text-transform: none; }\n\n\/* buttons: two classes so core's own .wp-block-button__link cannot win *\/\n.bp-adv .wp-block-buttons { display: flex; justify-content: center;\n  margin-block: 0 var(--bp-s-4); }\n.bp-adv .wp-block-button__link {\n  display: inline-flex; align-items: center; justify-content: center; min-height: 48px;\n  background: var(--bp-teal); color: var(--bp-white); font-size: var(--bp-fs-btn);\n  font-weight: 700; line-height: 1.2; border-radius: var(--bp-radius-btn);\n  padding: 15px 44px; text-decoration: none; transition: background 250ms ease;\n  box-shadow: var(--bp-shadow);\n}\n.bp-adv .wp-block-button__link:hover { background: var(--bp-olive); color: var(--bp-white); }\n\n\/* --- slot 1: pre-headline, headline, sub-headline (Jesse's headline skill) --- *\/\n.bp-adv .bp-adv-preheadline {\n  color: var(--bp-forest); font-size: var(--bp-fs-pre); font-weight: 600; line-height: 1.5;\n  border-left: 4px solid var(--bp-lime); padding-left: var(--bp-s-3);\n  margin-block: 0 var(--bp-s-4);\n}\n.bp-adv .bp-adv-subheadline { font-size: 21px; line-height: 1.5; font-weight: 600;\n  color: var(--bp-forest); margin-block: 0 var(--bp-s-5); }\n.bp-adv .bp-adv-standfirst { font-size: 19px; line-height: 1.65;\n  margin-block: 0 var(--bp-s-5); }\n.bp-adv .bp-adv-lede { font-size: 18px; line-height: 1.7;\n  margin-block: 0 var(--bp-s-5); }\n.bp-adv .bp-adv-byline { font-size: var(--bp-fs-small); color: var(--bp-foot);\n  line-height: 1.6; margin-block: 0 var(--bp-s-5); }\n.bp-adv .bp-adv-socialproof { font-size: var(--bp-fs-small); color: var(--bp-foot);\n  margin-block: 0 var(--bp-s-5); }\n\/* the offer headline above the CTA. Jesse asked for a second H1 here; the brand\n   doc's accessibility rule is one h1 per page, so it is rendered at H1 size and\n   stays an h2 element. Named in the close as the one design conflict. *\/\n.bp-adv h2.bp-adv-offerhead {\n  font-size: var(--bp-fs-h1); font-weight: 700; line-height: 1.22;\n  margin-block: 0 var(--bp-s-4); text-align: center; color: var(--bp-ink);\n  background: none; padding: 0; border: 0; border-radius: 0;\n}\n\n\/* --- Written by + Verified by. The avatar is the first child and spans the\n       three text rows, so the whole box is four ordinary paragraphs and stays\n       editable without nested columns. ---------------------------------------- *\/\n.bp-adv .bp-adv-authors {\n  background: var(--bp-white); border: 1px solid var(--bp-sand);\n  border-top: 4px solid var(--bp-lime); border-radius: var(--bp-radius-card);\n  box-shadow: var(--bp-shadow); padding: var(--bp-s-5);\n  margin-block: 0 var(--bp-s-4);\n  \/* auto-fit, so switching the verified box off leaves one full-width author\n     rather than a half-empty card *\/\n  display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));\n  gap: var(--bp-s-5); align-items: start;\n}\n.bp-adv .bp-adv-author {\n  display: grid; grid-template-columns: 62px 1fr; gap: 0 var(--bp-s-3);\n  align-items: start; min-width: 0;\n}\n.bp-adv .bp-adv-avatar {\n  grid-row: 1 \/ span 3; width: 62px; height: 62px; border-radius: 50%;\n  background: #B7CB331F; border: 2px dashed var(--bp-olive);\n  display: flex; align-items: center; justify-content: center;\n  font-size: 10px; font-weight: 700; letter-spacing: 0.06em; color: var(--bp-forest);\n  margin-block: 0;\n}\n.bp-adv .bp-adv-author.is-placeholder .bp-adv-avatar {\n  border-color: var(--bp-sand); background: #fff; color: var(--bp-foot); }\n.bp-adv .bp-adv-author-role {\n  font-size: 11px; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase;\n  color: var(--bp-forest); line-height: 1.6; margin-block: 0; }\n.bp-adv .bp-adv-author.is-placeholder .bp-adv-author-role { color: var(--bp-foot); }\n.bp-adv .bp-adv-author-name { font-size: 17px; font-weight: 700; line-height: 1.35;\n  margin-block: 0; }\n.bp-adv .bp-adv-author-cred { font-size: var(--bp-fs-foot); color: var(--bp-foot);\n  line-height: 1.55; margin-block: 0; }\n\/* the optional wrapper must not break the two-column grid of the box *\/\n.bp-adv .bp-adv-authors > .bp-optional { display: contents; }\n.bp-adv .bp-adv-authors > .bp-optional.bp-off { display: none !important; }\n\n\/* --- placeholders: image slot, video slot ---------------------------------- *\/\n.bp-adv .bp-slot {\n  display: flex; align-items: center; justify-content: center; text-align: center;\n  min-height: 180px; padding: var(--bp-s-4); margin-block: var(--bp-s-5) 0;\n  border: 2px dashed var(--bp-olive); border-radius: var(--bp-radius-photo);\n  background: #B7CB331F; color: var(--bp-forest);\n}\n.bp-adv .bp-slot p { font-size: var(--bp-fs-small); font-weight: 700; margin-block: 0; }\n.bp-adv .bp-slot--video { min-height: 260px; }\n\n\/* --- mid-article CTA band --------------------------------------------------- *\/\n.bp-adv .bp-adv-midcta {\n  background: var(--bp-grad-lime); border: 1px solid var(--bp-lime);\n  border-radius: var(--bp-radius-card); padding: var(--bp-s-5) var(--bp-s-4);\n  margin-block: var(--bp-s-6); text-align: center;\n}\n.bp-adv .bp-adv-midcta .wp-block-buttons { margin-block-end: var(--bp-s-2); }\n.bp-adv .bp-adv-midcta .bp-adv-foot { margin-block: 0; }\n\n\/* the closing CTA is one named unit in List View, so it moves and toggles as a\n   whole. It carries no box of its own: the spacing must read exactly as it does\n   on the approved page, where the three parts are plain siblings. *\/\n.bp-adv .bp-adv-ctablock { margin-block: 0 var(--bp-s-5); }\n.bp-adv .bp-adv-ctablock .wp-block-buttons { margin-block-end: var(--bp-s-4); }\n.bp-adv .bp-adv-ctablock .bp-adv-foot { margin-block: 0; }\n\n\/* --- the condition, slot 8: the results page reference-card shape ----------- *\/\n.bp-adv .bp-adv-condition {\n  background: var(--bp-white); border: 1px solid var(--bp-sand);\n  border-left: 5px solid var(--bp-lime); border-radius: var(--bp-radius-btn);\n  padding: var(--bp-s-4) var(--bp-s-5); font-weight: 600; box-shadow: var(--bp-shadow);\n}\n\n\/* --- the numbers card: the results page focus panel, same gradient, same\n       radius, same lime figures (\"use more of that design\") ------------------ *\/\n.bp-adv .bp-adv-numcard {\n  background: linear-gradient(135deg, var(--bp-teal) 0%, var(--bp-forest) 100%);\n  border-radius: var(--bp-radius-card);\n  padding: var(--bp-s-6) var(--bp-s-5) var(--bp-s-5);\n  box-shadow: var(--bp-shadow); margin-block: var(--bp-s-5) 0;\n  position: relative; overflow: hidden;\n}\n.bp-adv .bp-adv-numcard::after {\n  content: \"\"; position: absolute; right: -70px; top: -70px; width: 240px; height: 240px;\n  border-radius: 50%; background: rgba(255,255,255,0.05); pointer-events: none;\n}\n.bp-adv .bp-adv-numcard .wp-block-columns {\n  position: relative; z-index: 1; gap: var(--bp-s-5); margin-block: 0; }\n.bp-adv .bp-adv-numcard .wp-block-column { min-width: 0; }\n.bp-adv .bp-adv-num-v { font-size: 44px; font-weight: 700; line-height: 1.12;\n  color: var(--bp-lime); text-align: center; margin-block: 0 var(--bp-s-2); }\n.bp-adv .bp-adv-num-l { font-size: var(--bp-fs-small); line-height: 1.5;\n  color: rgba(255,255,255,0.92); text-align: center; margin-block: 0; }\n.bp-adv .bp-adv-numsrc { margin-block: var(--bp-s-5) 0; }\n\n\/* --- the proof slot: a dashed card until a consented quote exists. 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Helder uitgelegd, met bronnen.\",\"inLanguage\":\"nl-NL\",\"dateModified\":\"2026-10-10\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/bioprofile.com\/biomarkers\/vrij-t4\/\"},\"isPartOf\":{\"@id\":\"https:\/\/bioprofile.com\/biomarkers\/vrij-t4\/\"},\"publisher\":{\"@id\":\"https:\/\/bioprofile.com\/#organization\"},\"about\":{\"@id\":\"https:\/\/bioprofile.com\/biomarkers\/vrij-t4\/#biomarker\"},\"citation\":[{\"@type\":\"CreativeWork\",\"name\":\"MedlinePlus, U.S. National Library of Medicine. Thyroxine (T4) Test. Geraadpleegd op 10 oktober 2026.\",\"url\":\"https:\/\/medlineplus.gov\/lab-tests\/thyroxine-t4-test\/\"},{\"@type\":\"CreativeWork\",\"name\":\"Labplusarts, het laboratorium waarmee BioProfile werkt: referentiewaarde bij de bepaling vrij t4 (FT4), 11,0 tot 21,0 pmol\/l. Lijst van 24 september 2026.\"},{\"@type\":\"CreativeWork\",\"name\":\"BioProfile, de pakketten van het bloedonderzoek en de waarden in elk pakket.\",\"url\":\"https:\/\/bioprofile.com\/bloedonderzoek\/\"}]},{\"@type\":\"MedicalTest\",\"@id\":\"https:\/\/bioprofile.com\/biomarkers\/vrij-t4\/#biomarker\",\"name\":\"Vrij T4\",\"alternateName\":[\"Free T4\"]}]}<\/script>\n\n\n\n<section class=\"wp-block-group bp-adv bp-biomarker bp-biomarker--page is-layout-flow wp-block-group-is-layout-flow\">\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity bp-adv-rule\"\/>\n\n\n\n<div class=\"wp-block-group bp-adv-sec bp-adv-sec--hero is-layout-flow wp-block-group-is-layout-flow\">\n\n<p class=\"bp-bm-crumbs wp-block-paragraph\"><a href=\"https:\/\/bioprofile.com\/en\/\">Home<\/a> \u203a <a href=\"https:\/\/bioprofile.com\/en\/biomarkers\/\">Biomarkers<\/a> \u203a <span>Free T4<\/span><\/p>\n\n\n\n<h1 class=\"wp-block-heading bp-adv-h1\">Free T4 (FT4): what your level tells you about your thyroid<\/h1>\n\n\n\n<p class=\"bp-adv-standfirst wp-block-paragraph\">Free T4 is the active form of the hormone thyroxine in your blood. A level that is too low or too high can point to a problem with your thyroid.<sup>[1]<\/sup><\/p>\n\n\n\n<p class=\"bp-adv-lede wp-block-paragraph\">On this page you can read what free T4 is, what the guidelines say about a low or high level, what affects your level and which values are best to look at alongside it.<\/p>\n\n\n\n<p class=\"bp-bm-names wp-block-paragraph\">Also known as: free thyroxine, free T4, thyroxine. At the lab: FT4.<\/p>\n\n\n\n<p class=\"bp-adv-byline wp-block-paragraph\">Updated on 10 October 2026<\/p>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec bp-adv-sec--wash is-layout-flow wp-block-group-is-layout-flow\">\n\n<div class=\"wp-block-group bp-bm-toc is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-inhoud\">On this page<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li><a href=\"#bp-in-het-kort\">In short<\/a><\/li>\n\n\n<li><a href=\"#bp-wat-is-vrij-t4\">What is free T4?<\/a><\/li>\n\n\n<li><a href=\"#bp-waarom-het-ertoe-doet\">Why your thyroid hormone matters<\/a><\/li>\n\n\n<li><a href=\"#bp-wat-je-waarde-zegt\">What your free T4 level tells you<\/a><\/li>\n\n\n<li><a href=\"#bp-wat-het-beinvloedt\">What affects your free T4<\/a><\/li>\n\n\n<li><a href=\"#bp-welke-pakketten\">Which BioProfile packages measure free T4<\/a><\/li>\n\n\n<li><a href=\"#bp-waarden-die-erbij-horen\">Related values<\/a><\/li>\n\n\n<li><a href=\"#bp-hoe-gemaakt\">How this page was made<\/a><\/li>\n\n\n<li><a href=\"#bp-bronnen\">Sources<\/a><\/li>\n\n<\/ul>\n\n<\/div>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-in-het-kort\">In short<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li>T4 is the main hormone your thyroid makes.<sup>[1]<\/sup><\/li>\n\n\n<li>Free T4 is the form that enters your tissues, where you need it.<sup>[1]<\/sup><\/li>\n\n\n<li>Too much or too little T4 can point to a problem with your thyroid.<sup>[1]<\/sup><\/li>\n\n\n<li>A T4 test on its own does not tell you enough, so TSH is usually measured as well.<sup>[1]<\/sup><\/li>\n\n<\/ul>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec bp-adv-sec--wash is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-wat-is-vrij-t4\">What is Free T4?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Your thyroid is a small, butterfly-shaped gland at the front of your neck. The main hormone it makes is called thyroxine, or T4.<sup>[1]<\/sup><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">T4 is found in your blood in two forms. Free T4 is the active form that enters your tissues. Bound T4 is attached to proteins and stays in your blood as a reserve until your tissues need it.<sup>[1]<\/sup><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A free T4 test measures only the free part. Medical experts consider this test more accurate than a total T4 test, which is why it is used more often.<sup>[1]<\/sup><\/p>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-waarom-het-ertoe-doet\">Why your thyroid hormone matters<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Thyroid hormones control how your body uses energy. They act on almost every organ. They affect your breathing, your heart rate, your weight, your digestion and your mood. In children, they also affect growth.<sup>[1]<\/sup><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Too little thyroid hormone slows your body down. For example, you may feel tired, your weight may go up, you may feel cold easily and your skin may become dry.<sup>[1]<\/sup><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Too much thyroid hormone speeds your body up. For example, your weight may drop even though you eat more than usual, your heart may beat fast or irregularly, and you may feel nervous or sleep badly.<sup>[1]<\/sup><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Symptoms differ from person to person. Thyroid problems often run in families, and that can be a reason to have your level measured.<sup>[1]<\/sup><\/p>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec bp-adv-sec--wash is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-wat-je-waarde-zegt\">What your Free T4 level tells you<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">The lab's reference range<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The lab BioProfile works with, Labplusarts, uses a reference range of 11.0 to 21.0 pmol\/l for free T4. The lab calls a level between these limits normal.<sup>[2]<\/sup><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Labplusarts reference value<\/h3>\n\n\n\n<figure class=\"wp-block-table bp-bm-table\"><table><thead><tr><th>Value<\/th><th>What it can mean<\/th><th>Who it is for<\/th><\/tr><\/thead><tbody><tr><td>11.0 to 21.0 pmol\/l<sup>[2]<\/sup><\/td><td>The lab calls a value between these limits normal<\/td><td>Results measured by Labplusarts<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"bp-bm-caption wp-block-paragraph\">Source: Labplusarts, the lab BioProfile works with. Reference range for free T4 (FT4).<sup>[2]<\/sup><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Free T4 too low<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A level below normal can point to a thyroid that is working too slowly. It can also point to an immune reaction in which your immune system attacks the thyroid, to certain stages of an inflamed thyroid, or to too much or too little iodine in your diet. Sometimes the pituitary gland is the cause, but that is rare. In a newborn baby, it can point to a thyroid that has worked too slowly since birth. A low level can also come from thyroid treatment, such as radiation, radioactive iodine or surgery.<sup>[1]<\/sup><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Free T4 too high<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A level above normal can point to a thyroid that is working too hard. It can also point to an immune reaction in which your immune system attacks the thyroid, to certain stages of an inflamed thyroid, or to an enlarged thyroid or a lump that makes too much hormone. Your doctor usually looks at your result alongside other thyroid values to see what it means.<sup>[1]<\/sup><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">BioProfile is working on its own zones for each value, from risk to optimal. A doctor reviews those zones before they appear in your result.<\/p>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-wat-het-beinvloedt\">What affects your Free T4<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Medicines and supplements<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Some medicines and supplements can affect your result. Tell your healthcare provider what you take. Do not stop taking a medicine without talking to them first.<sup>[1]<\/sup><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Thyroid hormone as a medicine<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Do you take thyroid hormone because your thyroid works too slowly? Then a T4 test can show how well that medicine is working.<sup>[1]<\/sup><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Iodine in your diet<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Too much or too little iodine in your diet can go together with a low T4.<sup>[1]<\/sup><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Your pituitary gland and brain<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">An abnormal T4 usually comes from the thyroid itself. Sometimes the cause lies in the pituitary gland, which makes too much or too little TSH, or in the hypothalamus, the part of your brain that controls the pituitary gland.<sup>[1]<\/sup><\/p>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec bp-adv-sec--wash is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-welke-pakketten\">Which BioProfile packages measure Free T4<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Free T4 is included in BioProfile 87, 121 and 150.<sup>[3]<\/sup><\/p>\n\n\n\n<div class=\"wp-block-buttons is-content-justification-center is-layout-flex wp-container-core-buttons-is-layout-3e41869c wp-block-buttons-is-layout-flex\">\n\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link wp-element-button\" href=\"https:\/\/bioprofile.com\/en\/blood-testing\/\">View the packages<\/a><\/div>\n\n<\/div>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-waarden-die-erbij-horen\">Values that go with it<\/h2>\n\n\n\n<ul class=\"wp-block-list bp-bm-related\">\n\n<li><a href=\"https:\/\/bioprofile.com\/en\/biomarkers\/tsh\/\">TSH<\/a>: tells your thyroid how much hormone to make, and is usually measured together with T4.<sup>[1]<\/sup><\/li>\n\n\n<li><strong>Selenium<\/strong>: helps build the wider picture, because a T4 test on its own does not tell you enough about your thyroid.<sup>[1]<\/sup><\/li>\n\n\n<li><strong>TPO antibodies<\/strong>: relevant to the question of whether an immune reaction against your thyroid is behind an abnormal T4.<sup>[1]<\/sup><\/li>\n\n\n<li><strong>Iodine<\/strong>: too much or too little iodine in your diet can go together with a low T4.<sup>[1]<\/sup><\/li>\n\n\n<li><strong>Free T3<\/strong>: another thyroid value, because T4 is usually looked at together with other thyroid tests.<sup>[1]<\/sup><\/li>\n\n<\/ul>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec bp-adv-sec--wash is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-hoe-gemaakt\">How this page was made<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The BioProfile editorial team wrote this page on 10 October 2026 from the sources below, which we read on 10 October 2026. Every number on this page appears in one of those sources, with that source's number next to it. An expert has yet to check this page; after that check, the expert's name and the date of the check will appear at the top. This page offers explanation, not a diagnosis. Discuss a value outside the range with your GP.<\/p>\n\n<\/div>\n\n\n\n<div class=\"wp-block-group bp-adv-sec bp-adv-sec--disclosure is-layout-flow wp-block-group-is-layout-flow\">\n\n<h2 class=\"wp-block-heading\" id=\"bp-bronnen\">Sources<\/h2>\n\n\n\n<ol class=\"wp-block-list bp-adv-srclist bp-bm-src\">\n\n<li>MedlinePlus, U.S. National Library of Medicine. Thyroxine (T4) Test. Accessed on 10 October 2026. <a href=\"https:\/\/medlineplus.gov\/lab-tests\/thyroxine-t4-test\/\" target=\"_blank\" rel=\"noopener\">https:\/\/medlineplus.gov\/lab-tests\/thyroxine-t4-test\/<\/a><\/li>\n\n\n<li>Labplusarts, the laboratory BioProfile works with: reference range for the free T4 (FT4) test, 11.0 to 21.0 pmol\/l. List dated 24 September 2026.<\/li>\n\n\n<li>BioProfile, the blood test packages and the values in each package. <a href=\"https:\/\/bioprofile.com\/en\/blood-testing\/\" target=\"_blank\" rel=\"noopener\">https:\/\/bioprofile.com\/en\/blood-testing\/<\/a><\/li>\n\n<\/ol>\n\n<\/div>\n\n<\/section>\n\n","protected":false},"excerpt":{"rendered":"<p>Home \u203a Biomarkers \u203a Free T4 Free T4 (FT4): what your level tells you about your thyroid Free T4 is the active form of the hormone thyroxine in your blood. A level that is too low or too high can point to a problem with your thyroid.[1] On this page you can read what free [&hellip;]<\/p>\n","protected":false},"author":18,"featured_media":0,"parent":6592,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"elementor_header_footer","meta":{"_yoast_wpseo_title":"Free T4 (FT4): what your level tells you | BioProfile","_yoast_wpseo_metadesc":"What is free T4, what can a low or high level mean, and which values do you look at alongside it? 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