HEALTH / Common Procedures: Blood tests

ALMOST everyone who goes into a hospital as an outpatient will have some blood taken from a vein for 'tests'. Laboratories can measure the blood content of thousands of substances, from chemicals to complex proteins such as antibodies to HIV. The test most commonly done is a full blood count (a relatively simple procedure, nowadays mostly fully automated) in which the numbers of red and white blood cells and the small blood-clotting cells, the platelets, are counted. The amount of red pigment, haemoglobin, is measured, and often a thin smear of the blood on a glass slide is stained and examined under a microscope. Often the results do no more than confirm the diagnosis made at the first consultation, but confirmation is reassuring for doctor and patient.

Firstly, the red cell count and other measurements will show whether the person is anaemic - defined as having less than the normal amount of haemoglobin. Symptoms of anaemia are unusual until the haemoglobin has fallen below 10g per 100ml. Anaemia of this severity is usually obvious enough from features such as pallor and lack of energy, but the blood count and the smear will refine the diagnosis, often pointing clearly to a cause such as recent blood loss, a vitamin or iron deficiency, or even some more serious disorder such as leukaemia.

The white cell count is also often no more than a confirmation of the working diagnosis of an infectious illness such as pneumonia, shown by an increase in the white cell numbers and of one kind, granulocytes, in particular. An increase in another kind of white cell, mononuclear cells, will suggest the possibility of some kinds of virus infection, tuberculosis, some tropical diseases, and exotic infections such as Rocky Mountain spotted fever.

An increase in eosinophilic white cells, which contain granules which stain a red colour in standard tests, occurs in many kinds of parasitic infections (such as worms in the intestines) as well as in allergic disorders such as hay fever and some kinds of asthma. It may also act as an alert to the possibility of an allergic reaction to a drug such as aspirin. Too few white cells may be a sinister sign, though some entirely healthy people go through their lives with only one-fifth of the so-called normal numbers in their blood. A really low white cell count indicates that the body's immune sytem is faltering. This may be due to damage to the cell factory in the bone marrow from poisonous chemicals, reactions to prescribed medicines, or replacement of the bone marrow by cancer cells. It is also a feature of some infectious illnesses such as typhoid and glandular fevers, malaria and Aids.

Examination of the blood smear is important in the diagnosis of anaemia and white cell disorders; the proportion of young cells, for example, will indicate how well the body is responding to the illness. The microscopic examination may also come up with surprises such as an unsuspected infection.

If the blood counts and smear are normal then a serious illness seems less likely, though it is not ruled out. We are still many years away from the science-fiction fantasy of a machine that takes a blood sample and, within a few seconds, produces a complete and reliable diagnosis.

Arts and Entertainment
Shades of glory: Roger Daltrey and Pete Townshend

Glastonbury Roger Daltrey and Pete Townshend will perform with Paul Weller as their warm-up act

Arts and Entertainment
Billie Piper as Brona in Penny Dreadful
tvReview: It’s business as usual in Victorian London. Let’s hope that changes as we get further into the new series spoiler alert
Arts and Entertainment
No Offence
tvReview: No Offence has characters who are larger than life and yet somehow completely true to life at the same time spoiler alert
Arts and Entertainment
The Queen (Kristin Scott Thomas) in The Audience
theatreReview: Stephen Daldry's direction is crisp in perfectly-timed revival
Arts and Entertainment

Will Poulter will play the shape-shifting monsterfilm
Have you tried new the Independent Digital Edition apps?
Arts and Entertainment

ebooksNow available in paperback
Arts and Entertainment

ebooks
  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?

ES Rentals

    Independent Dating
    and  

    By clicking 'Search' you
    are agreeing to our
    Terms of Use.

    General Election 2015: Ed Miliband's unlikely journey from hapless geek to heart-throb

    Miliband's unlikely journey from hapless geek to heart-throb

    He was meant to be Labour's biggest handicap - but has become almost an asset
    General Election 2015: A guide to the smaller parties, from the the National Health Action Party to the Church of the Militant Elvis Party

    On the margins

    From Militant Elvis to Women's Equality: a guide to the underdogs standing in the election
    Amr Darrag: Ex-Muslim Brotherhood minister in exile still believes Egypt's military regime can be replaced with 'moderate' Islamic rule

    'This is the battle of young Egypt for the future of our country'

    Ex-Muslim Brotherhood minister Amr Darrag still believes the opposition can rid Egypt of its military regime and replace it with 'moderate' Islamic rule, he tells Robert Fisk
    Why patients must rely less on doctors: Improving our own health is the 'blockbuster drug of the century'

    Why patients must rely less on doctors

    Improving our own health is the 'blockbuster drug of the century'
    Sarah Lucas is the perfect artist to represent Britain at the Venice Biennale

    Flesh in Venice

    Sarah Lucas has filled the British pavilion at the Venice Biennale with slinky cats and casts of her female friends' private parts. It makes you proud to be a woman, says Karen Wright
    11 best anti-ageing day creams

    11 best anti-ageing day creams

    Slow down the ageing process with one of these high-performance, hardworking anti-agers
    Juventus 2 Real Madrid 1: Five things we learnt, including Iker Casillas is past it and Carlos Tevez remains effective

    Juventus vs Real Madrid

    Five things we learnt from the Italian's Champions League first leg win over the Spanish giants
    Ashes 2015: Test series looks a lost cause for England... whoever takes over as ECB director of cricket

    Ashes series looks a lost cause for England...

    Whoever takes over as ECB director of cricket, says Stephen Brenkley
    Fishing for votes with Nigel Farage: The Ukip leader shows how he can work an audience as he casts his line to the disaffected of Grimsby

    Fishing is on Nigel Farage's mind

    Ukip leader casts a line to the disaffected
    Who is bombing whom in the Middle East? It's amazing they don't all hit each other

    Who is bombing whom in the Middle East?

    Robert Fisk untangles the countries and factions
    China's influence on fashion: At the top of the game both creatively and commercially

    China's influence on fashion

    At the top of the game both creatively and commercially
    Lord O’Donnell: Former cabinet secretary on the election and life away from the levers of power

    The man known as GOD has a reputation for getting the job done

    Lord O'Donnell's three principles of rule
    Rainbow shades: It's all bright on the night

    Rainbow shades

    It's all bright on the night
    'It was first time I had ever tasted chocolate. I kept a piece, and when Amsterdam was liberated, I gave it to the first Allied soldier I saw'

    Bread from heaven

    Dutch survivors thank RAF for World War II drop that saved millions
    Britain will be 'run for the wealthy and powerful' if Tories retain power - Labour

    How 'the Axe' helped Labour

    UK will be 'run for the wealthy and powerful' if Tories retain power