Vitamins, minerals and amino acids
Vitamine K2
The amount of vitamin K2 in the blood; a single value says little about vitamin K status.
Everything about this testWhat it measures
Vitamin K2 is the collective name for the menaquinones, labeled MK-4 to MK-14. They differ in the length of their tail and therefore in how long they stay in the blood. The body makes MK-4 itself from vitamin K1; the longer forms are made mainly by gut bacteria and are found in fermented food, cheese and egg yolk. Like vitamin K1, vitamin K2 helps activate clotting proteins and proteins in bone and the blood vessel wall.
- A low intake or absorption of vitamin K2, for example with problems with fat absorption
- The effect of a vitamin K2 supplement on the blood level
High
A high value is almost always caused by a supplement or by food shortly before the blood draw, such as fermented products, cheese or egg yolk. There are no known symptoms or diseases that go with a high value; an excess of vitamin K has not been described as harmful in the Netherlands. However, for anyone using a coumarin-type blood thinner, a supplement with a lot of vitamin K does matter, because it disturbs the dose setting.
Low
A low or unmeasurable value is the normal result in people who do not take a supplement: the menaquinones are present in the blood in very small amounts and disappear from it quickly. So a low value does not mean there is a deficiency in the bone or blood vessel wall. With problems absorbing fats from the gut, the value can be truly low. Symptoms from a vitamin K deficiency involve a tendency to bleed, and that is better read from the clotting test (PT or INR).
If your result is abnormal
An abnormal value on its own usually does not lead to further testing. With a tendency to bleed, the GP looks at clotting (PT or INR) and at causes of poor fat absorption. With osteoporosis, the approach follows from the bone density scan and the risk of falling, not from this result.
Reliability
The body's vitamin K status is hard to read from a single blood value, and the meaning of an abnormal vitamin K2 value has been little studied. The concentrations are very low and fluctuate strongly with diet and with the form (MK-4 disappears within hours, MK-7 stays much longer), and there is no agreed cut-off value. Whether extra vitamin K prevents fractures has not been sufficiently shown; the guideline on osteoporosis and fracture prevention therefore does not recommend vitamin K supplements, not even with a low blood value.
Limitations
- The result depends strongly on diet and on any supplements in the days and hours before the blood draw.
- The different forms (MK-4, MK-7 and longer menaquinones) stay in the blood for different lengths of time; which forms the laboratory includes differs per method.
- Coumarin-type blood thinners (acenocoumarol, phenprocoumon) block the action of vitamin K and not the level; a normal result then says nothing about clotting, and extra vitamin K actually disturbs the dose setting of these medicines.
- There are no standardized reference values; laboratories use their own methods and limits.
How common is this
A confirmed vitamin K deficiency is rare in adults in the Netherlands. How often a low vitamin K2 value in the blood occurs is not known, because there is no agreed cut-off value and little research has been done on it.
Who is this useful for
The result says little in people without symptoms. Even with osteoporosis or an increased risk of fractures, the result changes little: it has not been shown that extra vitamin K prevents fractures. Anyone who wants to know whether clotting works well gains more from the prothrombin time (PT or INR).
Downsides and risks
- A low result can cause unnecessary worry, while a low value is actually normal in people who do not take a supplement.
- A low result can lead to buying supplements whose benefit for bones has not been shown, and which are dangerous when using a coumarin blood thinner.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results