Cookie policy: This site uses cookies (small files stored on your computer) to simplify and improve your experience of this website. Cookies are small text files stored on the device you are using to access this website. For more information please take a look at our terms and conditions. Some parts of the site may not work properly if you choose not to accept cookies.

Join

Subscribe or Register

Existing user? Login

Whys, whats and whens of blood tests

By Pamela Mason

Most pharmacists will be familiar with the “pin-prick” used to obtain a few drops of blood from a finger tip or ear lobe to measure blood-glucose levels. For other blood tests, blood is usually drawn from the median vein in the antecubital fossa (area in front of the elbow), after applying a tourniquet to the upper arm. Typically, a 10 or 20ml syringe is used, but the amount of blood collected will depend on the tests requested and the number of sample tubes to be filled. For blood gases, arterial blood (drawn at the wrist) is required and the procedure is usually more painful than venous blood collection.

Full blood count

The most commonly requested blood test is the full blood count (FBC), which includes an assessment of the number, size and appearance of the three cellular elements in blood: erythrocytes (red cells), leucocytes (white cells) and thrombocytes (platelets). It can, therefore, be used to detect anaemia, leukaemia, blood clotting problems and many other conditions. Typical parameters with their reference ranges are shown in Panel 1 (p420) and are described below. It should be noted that reference ranges can vary, depending on the laboratory used.

Red blood cell tests

Tests relating to erythrocytes are used primarily to diagnose and investigate the possible causes of anaemia.

Red cell count

The red cell count (RCC) is decreased in anaemia and raised in dehydration. A high RCC also indicates polycythaemia (abnormal increase in erythrocyte production by the bone marrow).

Packed cell volume and mean cell volume

The packed cell volume (PCV) or “haematocrit” is the percentage of the total blood volume occupied by red cells. Traditionally, this has been determined by centrifuging blood in a microhaematocrit tube and measuring the height of the red cell column, but now automated analysers are used to calculate PCV. Centrifuging causes the components of the blood to separate. Red cells move to the bottom of the tube and plasma to the top, with a “buffy coat” (which contains leucocytes and platelets) in the middle.The appearance of the centrifuged sample can also provide subjective information about the patient’s health. For example, the colour and clarity of the plasma can suggest jaundice (dark plasma) or lipaemia (turbid plasma).

PCV can be used as a screening tool for anaemia and to indicate the degree of fluid loss in dehydration. A drop in PCV can also indicate internal haemorrhage before any other symptoms become apparent. PCV is raised in polycythaemia and in chronic hypoxia associated with pulmonary disease and congenital heart disease.

Download the attached PDF to read the full article.

Citation: The Pharmaceutical Journal URI: 10997011

Readers' comments (1)

Have your say

For commenting, please login or register as a user and agree to our Community Guidelines. You will be re-directed back to this page where you will have the ability to comment.

Recommended from Pharmaceutical Press

  • Workplace Drug Testing

    Workplace Drug Testing

    Explains drug testing regulatory frameworks and all aspects of drug analysis. Case studies of successful programmes are included.

    £79.00Buy now
  • Pharmaceutical Capsules

    Pharmaceutical Capsules

    Covers all aspects of capsule technology. An essential resource for all those involved in the development, manufacture and testing of capsules.

    £68.00Buy now
  • Suppositories

    Suppositories

    A detailed review of suppository dosage forms. For all those involved in the formulation, development, manufacture and testing of suppositories.

    £69.00Buy now
  • Pharmacy OSCEs

    Pharmacy OSCEs

    The only pharmacy-specific OSCE revision guide. This easy-to-use book covers the key competencies that will be tested in your exams.

    £24.00Buy now
  • MCQs in Clinical Pharmacy

    MCQs in Clinical Pharmacy

    Four practice tests, each with 80 practice-oriented MCQs. Assess your knowledge of clinical issues, evaluative and analytical skills.

    £24.00Buy now

Search an extensive range of the world’s most trusted resources

Powered by MedicinesComplete
  • Print
  • Share
  • Comment
  • Save
  • Print Friendly Version of this pagePrint Get a PDF version of this webpagePDF

Supplementary information

Newsletter Sign-up

Want to keep up with the latest news, comment and CPD articles in pharmacy and science? Subscribe to our free alerts.