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Reference ranges are supplied strictly for guidance only, and these should be used rather than those quoted in textbooks, diaries, etc, as both methods and units vary from department to department.

These should not be published as methodology changes in line with the introduction of new techniques the ranges become outdated and therefore are subject to constant review.

The current reference/therapeutic range is always included with the final report. 5% of the healthy population will have results marginally outside the quoted reference range. Ranges may be affected by age, gender, ethnic group, pregnancy, time of sampling and many other factors. Detailed information or advice on interpretation is always available from the laboratory.

Validity of results

Results are automatically validated if they are within preset ranges and have no error flags from the instruments, eg, Haemolysis, Lipaemia and Icterus. Ranges have been discussed and approved by senior scientists and consultant staff.

Results outside these ranges are scrutinised by qualified staff and authorised HCPC registered Biomedical Scientists or the duty Biochemist/Medic or Consultant. Comments may be appended and additional analyses undertaken based on the clinical details provided and on previous results.

Whilst internal and external quality assurance programmes are in operation to ensure accuracy and precision of results, occasionally random errors may occur and escape detection.

The clinician is often best placed to detect such errors. Therefore if you doubt the validity of a result, it is vital that you contact the relevant ‘Advice/Interpretation’ extension at once so that we can investigate and re-test samples whenever possible.

Please remember that certain factors may affect and possibly invalidate some test results, causing potential biological and analytical interference.

Examples include blood transfusion and other intravenous fluids, antibiotics, anticoagulants, drugs, timing of specimen in relation to drug dose, time of day, fasting status, type of tube.

A common problem which may affect the reliability of results is a delay in transport to the lab, especially if it is critical that the sample is received on ice or within a specific time limit. This is described in the table of tests if relevant to a particular test.

It is important to remember to supply details of drug dose and timing, as prompted in ICE, or on a handwritten request.

GP samples

In order to maintain sample viability there is a requirement for samples to arrive within the target times outlined.

For the routine Biochemistry blood profile tests, blood glucose and HbA1c and endocrine tests that are collected in primary care the target time from venepuncture to delivery in the laboratory is four hours with a maximum of six hours.

This includes samples for PTH collected into EDTA tubes. A small number of specialised tests must be delivered to the laboratory in under this time and/or be transported on ice as indicated. These tests are not ones that would normally be collected in primary care.

Advice on these specialised tests is provided on a test by test basis by the departmental duty biochemist (0161 276 1234 bleep 4375).


(Last reviewed November 2019)