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
Blackman: Landscape of children’s literature does not reflect the cultural diversity of young people
booksMalorie Blackman appeals for a better ethnic mix of authors and characters and the illustrator Quentin Blake comes to the rescue
Arts and Entertainment
'Eminem's recovery from substance abuse has made him a more potent performer, with physical charisma and energy he never had before'
musicReview: Wembley Stadium ***
Arts and Entertainment
‘Dawn of Planet of the Apes’ also looks set for success in the Chinese market

film
News
Arts and Entertainment
The successful ITV drama Broadchurch starring David Tenant and Olivia Coleman came to an end tonight

tv
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
Arts and Entertainment
Chocolat author Joanne Harris has spoken about the financial struggles most authors face

books
Arts and Entertainment
A scene from How To Train Your Dragon 2

Review: Imaginative storytelling returns with vigour

film
Arts and Entertainment
Josh Hutcherson, Donald Sutherland and Jena Malone in Mockinjay: Part 1

film
Arts and Entertainment

film
Arts and Entertainment
Characters in the new series are based on real people, say its creators, unlike Arya and Clegane the Dog in ‘Game of Thrones’
tv
Arts and Entertainment
A waxwork of Jane Austen has been unveiled at The Jane Austen Centre in Bath

books
Arts and Entertainment
Britney Spears has been caught singing without Auto-Tune

music
Arts and Entertainment
Unless films such as Guardians of the Galaxy, pictured, can buck the trend, this summer could be the first in 13 years that not a single Hollywood blockbuster takes $300m

tv
Arts and Entertainment
Miley Cyrus has her magic LSD brain stolen in this crazy video produced with The Flaming Lips

music
Arts and Entertainment
Gay icons: Sesame Street's Bert (right) and Ernie

tv
Arts and Entertainment
Singer Robin Thicke and actress Paula Patton

music
Arts and Entertainment
The new film will be shot in the same studios as the Harry Potter films

books
Arts and Entertainment
Duncan Bannatyne left school at 15 and was still penniless at 29

Bannatyne leaves Dragon's Den

TV
Arts and Entertainment
The French economist Thomas Piketty wrote that global inequality has worsened

books
Arts and Entertainment
David Tennant and Benedict Cumberbatch

TV
Arts and Entertainment
Ben Affleck plays a despondent Nick Dunne in David Fincher's 'Gone Girl'

film
Arts and Entertainment
Pete Doherty (L) and Carl Barât look at the scene as people begin to be crushed

music
Arts and Entertainment

tv
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
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.

    Iraq crisis: How Saudi Arabia helped Isis take over the north of the country

    How Saudi Arabia helped Isis take over northern Iraq

    A speech by an ex-MI6 boss hints at a plan going back over a decade. In some areas, being Shia is akin to being a Jew in Nazi Germany, says Patrick Cockburn
    The evolution of Andy Serkis: First Gollum, then King Kong - now the actor is swinging through the trees in Dawn of the Planet of the Apes

    The evolution of Andy Serkis

    First Gollum, then King Kong - now the actor is swinging through the trees in Dawn of the Planet of the Apes
    You thought 'Benefits Street' was controversial: Follow-up documentary 'Immigrant Street' has got locals worried

    You thought 'Benefits Street' was controversial...

    Follow-up documentary 'Immigrant Street' has got locals worried
    Refugee children from Central America let down by Washington's high ideals

    Refugee children let down by Washington's high ideals

    Democrats and Republicans refuse to set aside their differences to cope with the influx of desperate Central Americas, says Rupert Cornwell
    Children's books are too white, says Laureate

    Children's books are too white, says Laureate

    Malorie Blackman appeals for a better ethnic mix of authors and characters and the illustrator Quentin Blake comes to the rescue
    Blackest is the new black: Scientists have developed a material so dark that you can't see it...

    Blackest is the new black

    Scientists have developed a material so dark that you can't see it...
    Matthew Barzun: America's diplomatic dude

    Matthew Barzun: America's diplomatic dude

    The US Ambassador to London holds 'jeans and beer' gigs at his official residence – it's all part of the job, he tells Chris Green
    Meet the Quantified Selfers: From heart rates to happiness, there is little this fast-growing, self-tracking community won't monitor

    Meet the 'Quantified Selfers'

    From heart rates to happiness, there is little this fast-growing, self-tracking community won't monitor
    Madani Younis: Five-star reviews are just the opening act for British theatre's first non-white artistic director

    Five-star reviews are just the opening act for British theatre's first non-white artistic director

    Madani Younis wants the neighbourhood to follow his work as closely as his audiences do
    Mrs Brown and her boys: are they having a laugh?

    Mrs Brown and her boys: are they having a laugh?

    When it comes to national stereotyping, the Irish – among others – know it can pay to play up to outsiders' expectations, says DJ Taylor
    Gavin Maxwell's bitter legacy: Was the otter man the wildlife champion he appeared to be?

    Otter man Gavin Maxwell's bitter legacy

    The aristocrat's eccentric devotion to his pets inspired a generation. But our greatest living nature writer believes his legacy has been quite toxic
    Joanna Rowsell: The World Champion cyclist on breaking her collarbone, shattering her teeth - and dealing with alopecia

    Joanna Rowsell: 'I wear my wig to look normal'

    The World Champion cyclist on breaking her collarbone, shattering her teeth - and dealing with alopecia
    Bill Granger recipes: Our chef gives raw ingredients a lift with his quick marinades

    Bill Granger's quick and delicious marinades

    Our chef's marinades are great for weekend barbecuing, but are also a delicious way of injecting flavour into, and breaking the monotony of, weekday meals
    Germany vs Argentina World Cup 2014 preview: Why Brazilians don't love their neighbours Argentina any more

    Anyone but Argentina – why Brazilians don’t love their neighbours any more

    The hosts will be supporting Germany in today's World Cup final, reports Alex Bellos
    The Open 2014: Time again to ask that major question - can Lee Westwood win at last?

    The Open 2014

    Time again to ask that major question - can Lee Westwood win at last?