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FAQs - Biochemistry

The lab analyses a huge number of different substances, including hormones, small molecules, electrolytes, proteins and different types of cells.  For results to make the most sense, these components need to stay at the same levels in the tubes as they do in the body.  Thus, we use preservatives to keep the blood stable.  Different components need different preservatives, hence the variety in tube colours.

At the University Hospitals of North Midlands, we use BD Vacutainer® Blood Collection Tubes.

Our test catalogue has information on which bottles are needed for which test.  If you can’t find the test you want, or you need further information, please contact the Duty Biochemist before taking any samples and we will be happy to assist.

Add-on tests can be requested by entering the request on the order comms systems, printing a label and sticking to a request form; and then sending the request form to the lab.  The current order comms system does not communicate add-on with our lab management system.  We do not need any additional patient labels.  The Duty Biochemist reviews the add-on requests throughout the day.  Add-on tests will be performed on the most recent patient sample.  If you wish for a test to be performed on a specific sample, please state this on the request forms.

The lab keeps samples for approximately 48 hours, after which they are disposed.  Please bear this in mind when requesting add-on tests. In addition, the appropriate sample type must be available for a test to be added on.  Finally, if there is insufficient sample volume, we cannot perform any more tests.  This is particularly a concern for paediatric samples.

Certain tests are not suitable to be added to existing samples.  These include bicarbonate and lactate.  In most cases, this is because the analyte is not stable upon storage.  Please send a further sample for analysis.

For tests which are crucial to the immediate management of the patient, telephone the Duty Biochemist (9 am – 7pm Mon-Fri), or bleep the on-call BMS (out of hours).  Please send a paper add-on request as well for audit purposes.

It’s really important that 24-hour urine collections are done correctly, as incomplete collections, over-collecting or under-collecting can have significant impact on the results.

Please see Instructions for collection of 24-hour urine samples. If you need further clarification, please contact the Duty Biochemist for assistance.  

Depending on the type of test, results can be available within an hour; or may take up to 8 weeks.  Most in-house tests are done the same day – this includes things like urea and electrolytes, liver function, thyroid function, adrenal function and pregnancy tests.  We do large numbers of these tests every day, so it makes sense to have them available throughout the day. 

Some tests aren’t done very frequently.  These are often tests requested by specialists, or follow-up tests after an initial set of results.  We often do these tests as a ‘batch’ – this means we process a number of patient samples on one day, and then don’t do them again for a week or so.  This means results can take 2-3 weeks to come through.  This doesn’t mean there’s anything wrong – it’s just that some analyses take longer than others to perform.

Finally, some tests are processed at other laboratories.  The test may require a particular piece of equipment, special expertise to perform, or it may simply be cost-effective to process samples from multiple hospitals at one site.  These tests often take 6-8 weeks for results to come back, as samples need to be sent from our lab, processed and analysed at the referral lab, results posted back to us, and we put them on the system.  However, if anything urgent is identified by the referral lab, then they will telephone us, and we will inform the relevant doctors as soon as possible.

Haemolysis (rupture of red blood cells in blood) can cause significant problems with certain assays, notably potassium and phosphate. Red blood cells contain significant amounts of potassium and phosphate, so if they are ruptured, additional potassium and phosphate is released into the serum/plasma.  This causes spuriously elevated results.  The lab measures haemolysis on samples, and if this is found to be excessive, results may be removed.

Haemolysis is usually a result of traumatic venepuncture and rough treatment of samples during transit. Once venesection is complete, do not vigorously shake samples – gently inverting is sufficient for mixing.

Tests can be rejected for numerous reasons.  These include: incorrect sample type, sample not labelled, request form/sample mismatch, sample not received in the lab within an appropriate timeframe or inappropriate request.  A comment will be attached to the rejected request, please read these carefully.  Contact the Duty Biochemist if further discussion is required.

The lab also operates minimal repeat intervals for a number of tests.  This reduces the lab workload by avoiding performing duplicate tests which provide no new clinical information.  If a repeat test is important for the clinical management of the patient, please state this on the request form.  Duplicate requests are reviewed by the Duty Biochemist, and can be authorised if clinically appropriate.  If a test has been rejected and you wish to reinstate it, contact the Duty Biochemist.  Please note that samples are kept for approximately 48 hours, after this they will be disposed of.

This is a very difficult question to answer, as it depends on a number of variables.  In Biochemistry, most tests are performed on serum/plasma, the volume of which depends on the patient’s haematocrit.  Certain tests require more serum/plasma than others, and multiple tests require more serum/plasma than one or two tests.

Please contact the Duty Biochemist to arrange a slot.  Tests are performed at RSUH Outpatients on Monday, Wednesday, Thursday and Fridays at 8:15/8:20 am.  The patient will need to fast overnight, and then come to RSUH Outpatients in time for the appointment.  A blood sample will be taken and then the patient will be given a glucose drink.  Two hours later, a further blood sample will be taken.  The patient is then free to go.

For General enquiries, please contact the Helpdesk.

For Clinical enquiries, please contact the Duty Biochemist.