BBC News Online looks at why it bought the company.

Who is the US company?

The company the government has bought is New York based Life Resources Incorporated, which already supplies plasma to the UK.

The government bought the company - for �50m - because US companies have been bought up by private suppliers and the government was told its supplies could be threatened.

Plasma is the fluid in which the red and white cells and platelets are carried around the body.

It contains clotting factors, antibodies, albumin and minerals.

It will be bought from Life Resources, and turned into plasma products by a UK company, Bio Products Laboratory.

Why has the government decided it is necessary to turn to the US for plasma?

It wants to guarantee a 'safe' supply for NHS patients.

The UK government has been using US blood products since 1998 to reduce the risk of patients contracting vCJD through infected products.

It chose the US because there have been no reported cases of vCJD there, and it is the only country which can provide the quantity of good quality plasma the NHS needs.

The NHS no longer uses plasma from British blood donors because they have, in theory, been exposed to vCJD through the food chain, whereas in the US, people have not.

What is plasma used for?

It is used to make the blood clotting agents albumin, immunoglobulin and Factor 8.

Each year the NHS uses :-

• 5,000 kilos of albumin for patients with burns, shock and major trauma,
• 2,000 kilos of intravenous immunoglobulin for patients with problems with their weakened immune systems
• 400,000 bottles of Factor 8, used to treat 3,000 haemophilia patients.

Are there other safety measures in place?

Yes. In July it was announced that fresh frozen plasma would be imported from America to treat new-born babies and children born after 1 January 1996.

For the last four years, plasma has been imported to make clotting agents such as Factor 8, Factor 9 and albumin, to treat adult haemophiliacs and patients who have clotting problems after surgery.

Other safety measures include not taking blood from high-risk donors, and testing all units of blood for the presence of infections such as HIV, hepatitis B and hepatitis C.

What is CJD?

CJD, or Creutzfeldt-Jakob Disease, is an infectious and deadly brain disease for which is there is no cure or treatment.

It causes personality change, loss of body function, and eventually death.

It is thought to be caused by rogue proteins called prions.

It can take years for symptoms to develop.

CJD is a member of the same class of diseases as Bovine Spongiform Encephalopathy (BSE), commonly known as Mad Cow Disease.

There are two forms of CJD, classical and a new form, variant (vCJD).

Sporadic CJD, which comprises 85-90% of all classical CJD cases, occurs spontaneously in the general population with no known cause or triggering event.

vCJD is a similar neuro-degenerative disease, but generally occurs in younger people and is believed to be caused by eating meat infected with BSE.

There are about 35 to 70 cases of CJD each year in the UK. Most are of the sporadic form. In total, 117 people in the UK have died from vCJD.

Another 11 are dying from the disease.

What is the risk of being infected with vCJD?

A report by the National CJD Surveillance Unit in Edinburgh, published in July this year estimated cases of vCJD would increase by around 20% each year.

It stressed numbers would still be very small.

But other experts said the number of cases was still uncertain and that the report simply contained "best estimates".