Procedure for taking clinical samples

• Specimen Collection & Containers
• Specimen Requirements

Specimen Collection & Containers

Back to Top

Contamination is a major consideration in trace element analysis and may arise from the collection procedure and the container itself. Good hygiene should be practiced when collecting specimens. Zinc and Aluminium contamination can arise from the powder used as lubricant in disposable gloves. Glass must not be used for specimens for Aluminium determination. Certain plastic specimen tubes also contain Aluminium. Zinc can be released by gel-separation systems, rubber stoppers & o-rings and be present in anti-coagulants. Lead can be released from rubber septa and Cadmium from orange stoppers. Becton Dickinson, Greiner and Sarstedt all manufacture products designated as being suitable for trace element investigation. Products from other manufacturers may be suitable but, unless marketed specifically for trace element analysis, batch variations can be problematical. “Secondary” tubes, used for the storage and transportation of separated plasma or serum, must also be contamination-free. Plastic tubes with simple, skirted, push-on or screw caps can be used. Apart from those with rubber o-rings (do not use!), contamination does not appear to be a major problem. It would be wise, however, to acid-wash a batch of tubes and set aside for trace element use. Alternatively, suitable tubes may be obtained from TekLab.

24-hour urine collections should be made in containers that have been acid washed (1 mol/litre HNO3) followed by rinsing with ultra-pure water; ideally, urine for Mercury measurement should be collected into (hard) polycarbonate containers to avoid loss by diffusion. Random urine samples or aliquots of 24-hour collections should be taken into 30 ml sterile “Universal” containers with plastic tops (not those with metal caps and/or rubber cap-liners). Those manufactured by Sterilin appear to be consistently free of significant trace element contamination and acid-washing is unnecessary.

Specimen Volume Requirements

Blood collection tubes hold volumes of 5 - 10 ml, the usual quantity taken under normal sampling circumstances. This is usually more than enough for analytical purposes and can permit a single specimen to be used for more than one analyte e.g. blood Lead & Cadmium or serum Copper, Zinc & Selenium. When sampling from young children and adults who are difficult to bleed, 2 ml paediatric collection tubes may be used. Analysis of specimens of very small volume will usually be attempted; however in such cases there is usually little scope for mishap, for checking an anomalous result or for the performance of multi-element analysis.

Specimen Requirements

Back to Top

ASSAY	SPECIMEN	VOLUME(ml)	Min. Vol.(ml)	CONTAINER1
Aluminium2	Plasma/Serum	5	2	Special Li-Heparin
Arsenic	Blood	10	5	K-EDTA
Arsenic	Urine	20	10	Sterile plastic
Cadmium3	Blood	5	2	K-EDTA
Cadmium	Urine	20	5	Sterile plastic
Copper	Plasma/Serum	5	2	No anti-coagulant
Copper	Urine	20	10	Sterile plastic
Lead4	Blood	5	2	K-EDTA
Lead	Urine	20	10	Sterile plastic
Mercury	Blood	10	5	Li-Heparin
Mercury	Urine	20	10	Sterile plastic
Selenium	Plasma/Serum	5	2	No anti-coagulant
Zinc5	Serum	5	2	No anti-coagulant

Notes to Table

1. Collection tubes certified for trace element analysis should be used whenever possible. Tubes not so certified may be satisfactory, but there is no guarantee of reproducibility between batches. Avoid all tubes containing a separation gel.
2. Glass collection tubes must not be used – contamination can occur through leaching of Aluminium from the glass.
3. Avoid tubes with orange caps – the latter may contain Cadmium as a colouring agent.
4. Avoid specimen tubes having a “flat”, annular cap with a rubber septum – the latter component of some tubes of this type may be contaminated with Lead during manufacture. Tubes of the Vacutainer type are satisfactory. Sarsted 1.3 ml K-EDTA tubes can contain small, but significant, amounts of Lead. The Li-Heparin equivalent is satisfactory.
5. No anti-coagulant is preferable unless the tube is “trace element designated”. Avoid collection tubes using gel-separation systems and storage tubes with caps sealed by a rubber O-ring; these tubes are likely to be contaminated with Zinc.