This
guide is intended for medical, nursing and laboratory staff as an aid to
making the most efficient use of the service provided by this laboratory for
trace elements monitoring. It should be used in conjunction with the Handbook
of the SAS Trace Elements Laboratories (Ed. A.W. Walker. 3rd Edition,
Guildford 1998) which is accessible on www.sas-centre.org.
The
Laboratory is CPA accredited. The Trace Elements Section has had Supraregional
Assay Service (SAS) designation since 1974, and is on the list of laboratories
‘approved’ by the Health and Safety Executive for the occupational
monitoring of lead and cadmium. Good practical working relationships are
maintained with the other members of the U.K. SAS and Associated Trace Element
Laboratories.
Analysis
is performed by atomic absorption spectrometry (flame and electro-thermal) and
inductively coupled plasma mass spectrometry (ICP-MS). Performance is
monitored by extensive participation in a number of External Quality
Assessment Schemes: NEQAS
(blood lead and cadmium); TEQAS
(eight analytes in blood, serum and urine); Quebec
(eight analytes in blood, serum and urine); SAS
(blood lead, serum aluminium, copper and zinc).
In addition, each batch analysis is monitored by the inclusion of
internal quality control materials.
The Service Offered
The
laboratory aims to provide a comprehensive advisory, analytical and
interpretational service for the following trace elements and toxic metals.
Essential
elements:
copper - plasma/serum & urine
selenium - plasma/serum & urine
zinc - serum & urine
Essential
elements / toxicity only:
chromium – blood,
plasma & urine
cobalt - urine
iron – urine
manganese – blood & urine
Non-essential
elements:
aluminium - plasma, urine, water &
dialysis fluid
arsenic - blood & urine
barium - serum & urine
cadmium - blood & urine
lead - blood & urine
lithium
- urine (occupational exposure only)
mercury
- blood & urine
nickel - urine
thallium - blood & urine
Multi-element screening of blood and urine and
the investigation of individual, less commonly encountered, non-essential
elements is possible using ICP-MS.
Complementary
analytes:
erythrocyte zinc protoporphyrin (ZPP) - blood
creatinine - urine
In
appropriate circumstances, analysis of other matrices such as tablets, powders
and liquid preparations will be attempted, but only following prior
consultation.
The
laboratory aims to provide a turn-around-time of not greater than 10 working
days for most analytes, batches for the frequently requested elements being
run as follows: serum copper, zinc and selenium - at least twice weekly; blood
lead, plasma and water aluminium and urine copper - weekly. IF APPROPRIATE
CLINICALLY, urgent requests can usually be handled, but with prior
consultation only. Printed reports can be faxed in advance of the hard copy.
Consultation
is available on the validity, feasibility and design of large-scale projects
e.g. clinical research studies and environmental investigations. Analyses will
be undertaken if appropriate.
Using the Service
The
service is open to clinicians and pathologists working in the NHS, Public
Health and Private Health Care sectors and to those medical officers
responsible for monitoring occupational exposure.
It
is most important that appropriate specimens are collected for a particular
investigation and that the containers used are contamination-free. Advice on
these points is given below and in the SAS Trace Elements Handbook. If in
doubt, please phone this laboratory.
For
most analytical requests, prior arrangement with the laboratory is not
necessary. However, please note that while a comprehensive nutritional
investigation (e.g. serum copper, selenium and zinc) on one individual may be
valid, the concept of a 'heavy metal screen' is more complex. Situations
prompting this line of enquiry, or those involving ‘unusual’ metals (e.g.
barium, thallium, uranium), should be discussed, in advance, with this
laboratory so as to enable a sensible analytical approach to the problem to be
followed. Similarly, specimens originating from projects such as clinical
studies and environmental investigations will not be processed without
appropriate prior discussion.
Specimens
should be fully documented with respect to the following:
Source details (hospital, surgery, firm) and first-line contact
Personal details of individual being investigated
including home post code
Time and date of collection
Reason for investigation
Details of diet or nutritional impairment or therapy
Details of treatment (e.g. chelation therapy)
Nature and duration of exposure to relevant trace element
Specimens,
securely boxed, should be dispatched to the laboratory by 1st Class Post or
Hospital Transport*. Specimens that need to be kept overnight or over a
week-end should be stored at 4oC and not frozen.
*New
packaging regulations came into force in July 2005, based on the UN-ECE
ADR2005, http://www.unece.org/trans/danger/publi/adr/adr_e.html
within Packing Instruction P650. To comply with the new legal
requirements, all packaging MUST be used and sealed correctly. The outer
container of the triple package MUST bear the words “Diagnostic Specimen”
or “Clinical Specimen” and also bear the UN 3373 diamond mark.
The
packing instructions are detailed in: http://www.hse.gov.uk/biosafety/biologagents.pdf,
in appendix 1.2 (Transport of infectious substances) as Packing Instruction P650 on page 58. Please note that the 100mm minimum external dimension requirement has been deleted from P650: http://www.unece.org/trans/danger/publi/adr/adr2005/ECE-TRANS-175-Corr1e.pdf
Contact Points
Mr.
T.M.T. Sheehan,
Principal Clinical Scientist
& Deputy Head of Department: 0121 507 6028 / 4137
Dr.
R.A. Braithwaite,
Head of Department: 0121 507 4134/5
Miss
Aleha Khatun,
Section Team Leader: 0121
507 4136 / 4137
Charges
All analyses, are
chargeable on a per test basis irrespective of origin.
Payment for NHS requests is the responsibility of the designated
budget-holder within the District, Trust or Fund-holding General Practice.
Unless
work is carried out as part of an agreed contract, invoices are issued
retrospectively at the end of each month. Each request for analysis must be
accompanied by full details of the
individual responsible for receiving statements and invoices; for new users of
the service, this must include written agreement to this responsibility.
Third party instructions to
invoice the company or patient directly are not acceptable.
Details
of the current charges for individual assays will be found in the separate
document "Charges for Laboratory Services".
Specimen collection and containers
Contamination
is a major consideration in trace elements analysis and may arise from both
the collection procedure and the container itself. Good hygiene should be
practiced when collecting specimens, especially at 'dirty' sites such as
factories. In the clinical setting, the situation may be more subtle: zinc and
aluminium contamination has arisen from the powder used as lubricant in
disposable gloves. Containers can
be problematic. Glass must not be used for specimens for aluminium
measurement. With respect to blood collection, zinc can be released by gel-
separation systems, rubber stoppers and O-rings and be present in
anti-coagulants. Lead can be released from rubber septa and cadmium from
orange stoppers. 'Secondary' tubes, used for the storage and transportation of
separated plasma or serum, must also be contamination-free. 24 hour urine
collections should be made into containers that have been acid washed (1 mol/L
HNO3, followed by ultra pure water rinse); ideally, urine for
mercury measurement should be collected into (hard) polycarbonate containers
to avoid loss by diffusion. Plastic 'Universal' containers (not
those with metal caps and/or rubber cap-liners) are suitable for aliquots of
24 hour collections and for 'spot' urine specimens. They do not require
acid-washing.
Preservatives such as boric acid
and thiomersal must not be used.
Specific
requirements are discussed in the notes on individual trace elements and
summarised in Table 1. Note that, with the exception of investigations for
Wilson’ Disease, a ‘spot’ urine is satisfactory most of the time. It
is the urine option of choice for out-patient investigation and for
occupational monitoring, when it should be collected at end of shift towards
the end of the working week. For individuals hospitalised for the
investigation and treatment of metals poisoning an aliquot of a 24 hour
collection is preferred
Appendix 1 lists a number of companies that manufacture specimen containers specified as being suitable for trace element analysis or have been found to be suitable for that purpose by this laboratory. Please note that a charge may be made (equal to the cost of the analysis) if it is necessary to check the contamination status of an empty duplicate tube received in parallel with a specimen.
Specimen volume requirements
The
blood collection tubes listed Table 1 use volumes of 5 - 10 mL, the usual
quantity 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 and cadmium, or serum copper, zinc and
selenium. When sampling from young children, and adults who are difficult to
bleed, 2 mL (or smaller) paediatric collection tubes should be used. Analysis
of specimens of very small volume will usually be attempted; however, there is
usually little scope for mishap, for checking an anomalous result or for the
performance of multi-element measurement. Such a minimum volume is listed for
each element and matrix.
In
the event of poisoning or exposure in which metals may be implicated, the
following combination of specimens should be obtained: 5 mL whole blood
(K-EDTA), 10 mL serum and 30 mL urine. Avoid glass containers and serum
gel-separation tubes!
NOTES ON INDIVIDUAL TRACE ELEMENTS
The Essential Elements
Copper (Cu) - plasma/serum
Indications - Deficiency, hepato-biliary dysfunction
(inc. Wilson's Disease), toxicity.
Specimen requirements - 5 mL serum /plasma (minimum 100
µL).
Comment – (1) Raised values are seen in inflammatory states
and with steroid hormone therapy. (2) When investigating Wilson’s Disease,
plasma/serum Cu measurement is only of value as an addition to plasma
caeruloplasmin concentration and 24 hour urinary Cu excretion.
Reference
values:
Term Neonates*:
0.2 - 0.7 mg/L
By 7 days*:
0.3 – 1.1 mg/L
Children > 6 mth* & adults:
0.7 - 1.6 mg/L
Pregnancy > 15/40:
1.6 - 2.5 mg/L
*
Note that in healthy term neonates there is a gradual increase in values
between one week and six months of age. This is a dynamic period and defining
a ‘normal’ serum copper at any one instant is difficult. In healthy,
premature infants, changes in serum copper concentrations appear to be related
to subsequent growth rate.
Copper (Cu) - urine
Indications - Hepato-biliary dysfunction (inc.
Wilson's Disease), toxicity, occupational exposure.
Specimen requirements - 20 mL aliquot of 24 hour
specimen collected into an acid-washed container. Spot urine acceptable for
investigating acute toxicity and occupational exposure. Note that a ‘spot’
urine is not suitable for Wilson’s Disease investigations as the
results are not easily interpreted.
Comment – (1) To distinguish Wilson's Disease from other forms of
hepatic dysfunction, may require measurement of 24 hour urinary Cu excretion
before and after penicillamine challenge. Consult this laboratory or the SAS
Trace Elements Handbook. (2) Cu IUDs do not appear to increase excretion of or
urine content of the element.
Reference
values: (pre-chelation)
Normal excretion usually
< 50 µg/24 hrs
Patients with cholestasis, hepatic cirrhosis,covert Wilson's Disease
> 50 µg/24 hrs
Patients with frank Wilson's Disease, acute hepatic crisis >100 ug/24 hr
Selenium (Se) - plasma/serum
Indications - deficiency, toxicity
Specimen requirements - 5 mL plasma/serum (minimum 50
µL). Separate without delay to prevent haemolysis.
Comment - plasma/serum Se is a good index of recent (months)
changes in intake of or exposure to the element. However it is an acute-phase
reactant and concomitant measurement of C-reactive protein may be useful in
some circumstances as an aid to interpreting low Se concentrations.
Reference
values:
<18 months:
30 - 50 µg/L
18 months - 4 years:
45 - 90 µg/L
5 - 16 years:
55 - 115 µg/L
Adults (>16 years):
70 - 130 µg/L
Selenium (Se) - urine
Indications - toxicity, occupational monitoring.
Specimen requirements - 20 mL
urine.
Comment - Of no value in investigating deficiency.
Reference
values:
Excretion usually: < 30 µg/g creatinine / < 50 µg/24 hrs
Zinc (Zn) - serum
Indications - deficiency
Specimen requirements - 5 mL serum (minimum volume: 100
µL).
Comments - A relatively crude index of zinc
status. May exhibit diurnal variation in 'healthy' individuals and is affected
by number of factors including acute phase reaction, certain drugs and
pregnancy. Concomitant measurement of C-reactive protein may be useful in some
circumstances as an aid to interpreting low Zn concentration.
Reference
values:
< 0.5 mg/L
May indicate zinc deficiency
0.5 - 0.7 mg/L
May have no clinical significance
0.7 - 1.6 mg/L
'Normal' range for all ages
> 1.6 mg/L
? Dietary supplement use.
Zinc (Zn) - urine
Indications - metabolic studies, chelation therapy,
occupational exposure to zinc fume.
Specimen requirements - 20 mL aliquot of 24 hour
collection; spot urine for occupational monitoring.
Comments - Of little value in assessing
deficiency. May be of value in monitoring the effect on zinc body burden of
extended chelation therapy for the removal of other metals.
Reference values:
Excretion usually:
200 - 1400 mg/24
hrs
Essential Elements – investigations for toxicity or exposure only
Chromium (Cr) – blood, plasma & urine
Indications – toxicity (including PN overload),
occupational exposure.
Specimen requirements - 5mL blood; EDTA (minimum
volume: 100 µL); 20 mL urine. For occupational monitoring, collect urine at
end of working week.
Comments
- (1). In
acute poisoning, measurement of Cr in whole blood and urine is the approach of
choice. Plasma and erythrocyte concentrations can yield information as to form
of the element involved. (2) For suspected PN overload, plasma measurement is
used.(3). For on-going occupational exposure, urine is the preferred specimen.
In cases where exposure has ceased, or has occurred sporadically, within the
last four weeks, blood measurement is more useful. In all circumstances
particular care is needed to avoid contamination when collecting specimens.
(4). Monitoring for Cr ‘deficiency’ is not undertaken because (a) the
problem has yet to be convincingly demonstrated in humans and (b) it is
extremely difficult to collect blood without contaminating it to
concentrations within the normal range.
Reference
range:
Blood:
< 2.0 µg/L
Serum/plasma:
< 0. 5 µg/L
Urine:
< 1.0 µg/g creatinine
Cobalt (Co) – urine
Indications – occupational exposure.
Specimen requirements – 20 mL urine collected end of
shift, towards the end of the working week.
Comments: Only known essential role is as component of Vitamin B12.
Investigation of ‘cobalt deficiency’ per se is, therefore, inappropriate
and would, in any event, be technically extremely difficult.
Reference
range:
Urine: <
1.0 µg/g creatinine
Iron (Fe) – urine
Indications
– iron
overload; monitoring chelation therapy
Specimen
requirements:
20 mL aliquot of a 24 hour collection.
Comments
–Primarily for investigations relating to haemochromatosis or transfusional
siderosis.
Reference
range:
Excretion usually:
< 50 µg / 24 hours
Manganese (Mn) – blood & urine
Indications – toxicity (particularly PN overload)
Specimen requirements: 5 mL blood (EDTA – minimum volume 100 µL);
20 mL urine.
Comments – (1). Blood measurement is the
approach of choice for investigating PN overload. (2) For other situations,
blood and urine should be sent, although the usefulness of analysis for
occupational monitoring purposes is questionable unless the exposure has been
gross. (3) Monitoring
for Mn ‘deficiency’ is not undertaken because (a) the problem has yet to
be convincingly demonstrated in humans and (b) it is extremely difficult to
collect blood without contaminating it to concentrations within the normal
range.
Reference range:
Blood:
children < 1 year:
7 – 18 µg/L
children > 1 year, adults:
4 – 12 µg/L
risk of toxicty:
> 20 µg/L
Urine:
< 1µg / g creatinine
The Non-essential Elements
Aluminium (Al) - plasma
Indications - chronic renal failure, occupational
exposure, gross environmental
exposure.
Specimen requirements - 5 mL plasma. (Minimum volume 50
µL) Special Al-free tubes must
be used! Send specimens to this laboratory unseparated.
Comments - The service is primarily for
monitoring situations in which patients with renal impairment may be exposed
to excessive amounts of Al by virtue of their treatment, i.e. chiefly those
with chronic renal failure, but also premature infants on long-term parenteral
feeding. For individuals with normal renal function, in most cases, this
measurement is of little value as plasma Al concentrations are an index of
very recent exposure only (days) and give no information on body burden.
Exceptions to this may be occupational and gross environmental exposure. In
these circumstances the laboratory must be contacted before specimens are
taken.
Reference
values: (Commission of the European Community [CEC]
Recommendations for patients receiving dialysis)
< 10 µg/L
Normal (no history of CRF)
< 60 µg/L
Desirable in CRF patients
> 60 µg/L
Excessive accumulation
> 100 µg/L
Cause for concern; high risk of toxicity in children
> 200 µg/L
Urgent action required: high risk of toxicity in all
Aluminium (Al) - water
Indications - Treatment of chronic renal failure by
dialysis
Specimen requirements - 2 x 10 mL per sampling point.
Special Al-free tubes must be used! These are available from this
laboratory.
Comments - This service is primarily for
monitoring the Al content of water used in renal dialysis systems. Duplicate
aliquots are taken from the mains supply and from the outlet of any water
purifier used in the system. Requests for analysis of water obtained in other
circumstances are likely to be inappropriate unless extensive precautions are
taken to avoid contamination with respect to both container and sampling.
Reference
values: (CEC Recommendations)
Maximum allowable concentration (MAC) for potable water:
200 µg/L
Guide Line Concentration (GLC) for potable water:
50 µg/L
MAC for water for preparation of dialysis fluid:
30 µg/L
Aluminium (Al) - dialysis fluid
Indications - Treatment of chronic renal failure by
dialysis
Specimen requirements - 2 x 10 mL. Special Al-free tubes must be used! These are available from this
laboratory.
Comments - If Al content is unacceptable, both
concentrate and water used for dilution should be investigated.
Reference
range: (CEC Recommendation)
MAC for dialysis fluid:
30 µg/L
Aluminium (Al) - urine
Indications - Occupational exposure, gross
environmental exposure.
Specimen requirements - 20 mL spot urine. Special
Al-free containers must be used. These are available from this laboratory.
Comments - Gives a slightly broader window of
exposure (weeks) than plasma Al, but again provides no useful data on body
burden. Useful as indicated above, but laboratory should be contacted before
specimens are taken.
Reference
range:
Excretion usually:
< 25 µg/24 hrs
Arsenic (As) – blood & urine
Indications – toxicity, occupational exposure.
Specimen requirements- 5 mL whole blood (EDTA) (minimum
volume: 100 µL). 20 mL urine. For occupational monitoring collect specimen at
end of working week.
Comments – (1). For acute poisoning both blood
and urine should be sent. (2) For suspected chronic exposure and for
occupational monitoring, urine is the specimen of choice in the first
instance. (3) It is important to know, if available, the nature and duration
of exposure as a sea food diet can produce considerable quantities of
detectable As and all forms of the element are excreted rapidly (48 hours).
(4). Analysis is made for total non-dietary arsenic.
Reference
range:
Blood:
< 10 µg/L (Inorganic As & metabolites)
Excretion (inorganic As & metabolites) usually:
< 10 µg/g creatinine
< 10 µg/24 hours
Barium (Ba) - serum & urine
Indications - acute & chronic poisoning;
occupational exposure.
Specimen requirements - 5 mL serum (minimum volume 100
µL); 20 mL urine.
Reference
range:
Serum:
< 1 µg/L
Urine:
< 4 µg/24 hr
Cadmium (Cd) - blood & urine
Indications - occupational exposure, environmental
exposure, acute & chronic poisoning
Specimen requirements - 5 mL whole blood; EDTA.
(Minimum volume 100µL); 20 mL urine.
Comments - (1). Blood is the first-choice matrix.
Urine Cd is not normally measured unless blood Cd is elevated. (2). Smokers
tend to have raised Cd concentrations.
Reference
range:
Blood:
Non-smoker:
< 3.0 µg/L
Smoker:
< 6.0 µg/L
Acceptable occupational exposure:
< 10.0 µg/L
Urine:
Non-smoker:
< 1.0 µg/g creatinine
Smoker:
< 3.0 µg/g creatinine
Acceptable occupational exposure:
< 10.0 µg/g creatinine