In this section
Specimen requirements and reference ranges are shown in the table of Biochemistry tests.
Blood samples
Avoid contamination – When taking a series of blood specimens, it essential that the serum sample is taken first, followed by lithium heparin samples then the fluoride samples and any EDTA tubes last of all. Failure to adhere to this sequence will lead to contamination of blood samples with anticoagulants/preservatives. This contamination produces spurious and invalid results.
Avoid haemolysis, drip contamination, adverse temperatures (over 30°C or less than 10°C, unless otherwise stated) and prolonged venous constriction.
Ensure thorough and instant mixing of blood with anticoagulant (heparin, fluoride EDTA or potassium EDTA) for plasma samples.
Do not transfer blood from one tube to another e.g. EDTA to Lithium Heparin.
Do not leave Clinical Biochemistry blood samples in the fridge (4°C) or overnight at room temperature. If in doubt, please contact the laboratory (Duty Biochemist bleep 4375) for advice.
Leaking blood tubes will be discarded.
Urine samples
Most of the urine assays are normally reported as a 24 hour output, and a full 24 hour collection is required. Please ensure that start and end dates and times are noted on the bottle label.
Random samples or overnight collections are adequate for some tests and these are marked in the table.
Some analyses require a specific preservative in the collection bottle – check before starting collection. Special bottles are held by the Biochemistry Department and can be collected from there or the reception area in the Clinical Sciences Centre by the portering service or ward staff.
Please complete the bottle label as well as the request form.
Creatinine clearances can only be calculated if the blood creatinine is measured within 24 hours of the 24 hour urine.
Pleural fluid samples
For general biochemistry collect into a fluoride tube, glucose into a fluoride oxalate and sample for acid base assessment collected into a blood gas syringe and treated as a blood gas specimen.
A simultaneous blood sample for general biochemistry into a tube and glucose into a fluoride tube will be helpful for interpretation. See Light’s criteria for evaluating pleural fluid.
Sample volumes
One fully filled tube will generally contain sufficient blood for analysis of all profiles listed above. However this does depend on the MCV of the patient and assumes that a minimum of 2mls of serum or plasma is able to be separated.
For single analytes 1ml of whole blood is usually sufficient.
For all assays not quoted above please send one full tube of the correct type, if collection of multiple tubes causes a problem please call the duty biochemist for advice.
- Faecal samples (for faecal sugar chromatography only)
- Potential for Biotin interference in Immunoassays
(Last reviewed November 2019)