Vitamin K
A fat-soluble vitamin essential for blood clotting and bone health. Its status is usually judged not by measuring the vitamin directly but by its effect — a deficiency prolongs clotting and raises the INR. It is also the vitamin that warfarin works against.
What it measures
Vitamin K is a fat-soluble vitamin the liver needs to make several of the proteins that allow blood to clot, and which also contributes to bone health. It comes from green leafy vegetables and is also made by gut bacteria. In practice, vitamin K status is rarely assessed by measuring the vitamin itself; instead it is judged by its function — the prothrombin time and INR, which lengthen when clotting-factor production falls. Deficiency in adults is uncommon and usually results from fat malabsorption (liver, pancreatic or bowel disease), long-term poor intake, or antibiotics wiping out gut bacteria; it causes easy bruising and bleeding with a raised INR. Newborn babies are naturally low in vitamin K and are given a dose at birth to prevent a serious bleeding disorder. Vitamin K is also central to how the blood thinner warfarin works — warfarin blocks vitamin K, and vitamin K is used to reverse its effect when the INR is dangerously high.
What a high value can mean
- Supplementation — the usual reason; not generally harmful.
- A high level is rarely the clinical concern — the important direction is deficiency and its effect on clotting.
What a low value can mean
- Fat malabsorption — liver, pancreatic or bowel disease; the commonest adult cause.
- Poor intake, or antibiotics reducing gut bacteria.
- Warfarin — deliberately antagonises vitamin K (this is how it thins the blood).
- Effect — a raised INR/prothrombin time, easy bruising and bleeding.
- Newborns — naturally low; given vitamin K at birth to prevent bleeding.
When to discuss with a doctor
Vitamin K deficiency is usually recognised through its effect — a prolonged prothrombin time or raised INR with bruising or bleeding — rather than by measuring the vitamin, which is not a routine test. It is worth considering in someone with fat malabsorption or liver disease who has unexplained bleeding or a raised INR, where giving vitamin K can correct it. In an emergency, a dangerously high INR (whether from warfarin or liver disease) with bleeding is treated urgently, sometimes with vitamin K. Newborns receive vitamin K routinely to prevent bleeding. Mediora.AI shows the INR alongside liver markers so a vitamin K-related clotting problem is visible in context; the interpretation and treatment belong with your doctor.