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Glossary of terms used on this site

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Term Definition

Joint bleeds (haemathrosis) are the single most crippling complication of severe haemophilia and can result in chronic disabling arthritis. While not life threatening they should never be left untreated, no matter how mild they appear. Signs and symptoms of a joint bleed are, pain, a reluctance to move the affected joint, swelling and warmth.


The study of blood formation and the diseases associated with alterations in the constituents of the blood.


Presence of blood in the urine.


To haemorrhage means to bleed or lose blood.

Heart attack

Heart attack (myocardial infarction or coronary thrombosis) is when part of the heart muscle dies because it has been starved of oxygen. Usually, this happens when a blood clot forms in one of the coronary arteries (blood vessels to the heart muscle), which blocks the blood supply. Occasionally, a blockage is caused by a spasm (sudden narrowing) of a coronary artery.

Heart bypass

An operation to bypass a narrowed section or sections of coronary arteries and improve the blood supply to the heart.


The surgical removal or disconnection of one side of the brain from the other.

hepatitis C virus (HCV)

Hepatitis C is a blood-borne viral infection. Very rarely it can also be passed on through other body fluids, such as through having unprotected sex. Drug users sharing needles are at particular risk, as is anyone whose blood has come into contact with the blood of someone infected with hepatitis C.


Hermaphroditism and intersex are older terms for a group of conditions increasingly referred to as Disorders of Sex Development (DSD) where there is a discrepancy in an individual between the external genitals and the internal genitals (the testes and ovaries).

Heterozygote (Heterozygous): Carrier

When referring to a particular trait or condition, an individual who has two different alleles, usually one normal and the other altered, at a particular locus.

Hickman line

A central (Hickman) line is a long, hollow tube made from silicone rubber. The central line is inserted under the skin of the chest into a vein. The space in the middle of the tube is called the lumen.

HLA-B27 gene

Research has shown that most people who have ankylosing spondylitis carry a particular gene known as human leukocyte antigen B27 (HLA-B27). Among people with ankylosing spondylitis, 9 out of 10 have HLA-B27.


Matched or identical, particularly when referring to chromosomes.

Homozygote (Homozygous)

When referring to a particular trait or condition, an individual who has two identical alleles at a particular locus.


Hormones are the body's chemical messengers. They travel in your bloodstream to tissues or organs. They work slowly, over time, and affect many different processes, including

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