Copper (Cu)
Copper is an essential component of numerous copper metalloenzymes that are required for normal oxidative metabolism, iron metabolism, free radical detoxification and synthesis of haemoglobin, elastin and collagen. Only small amounts of copper are required in the diet (1.0 mg/day). Copper is absorbed in the proximal intestine. Copper is normally excreted in bile and so an increase in plasma and urine copper may occur in cholestatic liver disease. Most circulating copper is in the form of caeruloplasmin. Oestrogens increase copper by increasing caeruloplasmin synthesis, so it can be two to three-fold higher in the last trimester of pregnancy and with the use of oral contraceptives. In neonates, copper is low (3-5 µmol/L) but increases gradually to adult values by one year of age. For this reason copper deficiency may occur especially in neonates on diets deficient in copper and they are at potential risk of bone disease. Plasma copper is sometimes requested when abuse is suspected in young children with unexplained bone fracture.
Copper deficiency is uncommon but may occur as a result of gastric surgery, untreated coeliac disease, misplaced duodenal tube and, more commonly, inhibition of its absorption because of high oral zinc ingestion (usually in excess of 75 mg/day) following zinc prescription or over-the-counter purchase of zinc supplements, high zinc enteral feeds, or over-application of zinc-containing dental adhesive (Fixodent). Symptoms are anaemia, neutropenia and in more severe cases ataxia and peripheral neuropathy.
Measurement of copper is centrally involved in the diagnosis of Wilson's Disease. Concentrations are usually low in plasma because of the impairment of its incorporation into caeruloplamin, the main copper carrying protein in the circulation, and high in urine and liver. Liver concentrations of over 250 µg/g dry weight are usually found. However, 3% of Wilson’s Disease patients have results < 50 µg/g and 13% of Wilson’s Disease patients have results of 50 to 250 µg/g.26 High concentrations may also be found in obstructive liver disease.26
Other rarer genetic causes of a low plasma copper are Menkes Disease and acaeruloplasminaemia.
Assessment of Status
Caeruloplasmin, and so copper, is a positive acute phase reactant and a detectable increase in plasma copper (by up to 30%) may be seen after infection, injury, or inflammation. In the first two days following elective surgery, plasma copper falls by around 10% (Table 1).27 Subsequently copper concentrations increase by up to 25% (Table 2).28 Occasionally in patients with a severe systemic inflammatory response plasma copper concentrations may fall substantially.
Recommended Daily Allowance
Adults: 1 mg/day.
Effect of Systemic Inflammatory Response on Plasma Copper Concentrations
Table 1: Baseline, peak/ trough and day 7 concentrations of plasma copper following elective surgery for knee arthroplasty (n = 20)27.
| Analyte | Baseline values |
Peak/trough (48 h) |
Final values (168 h) |
Friedman (0 to 168 h) |
| CRP (mg/L) | <6 (<6–17) | 160 (83-240) | 29 (10-87) | p < 0.001 |
| Copper (μmol/L) | 18.1 ± 4.4 | 16.0 ± 3.9 | 22.0 ± 4.6 | p < 0.001 |
Table 2: Distribution of median plasma copper concentrations according to increments of CRP concentrations (n = 2176)28.
|
CRP (mg/L) |
n |
Median Cu (μmol/L) |
p |
| ≤ 5 | 1133 | 16.1 | - |
| > 5 to 10 | 309 | 18.4 | <0.001 |
| > 10 to 20 | 227 | 19.8 | <0.001 |
| > 20 to 40 | 174 | 20.6 | <0.001 |
| > 40 to 80 | 142 | 19.3 | <0.001 |
| > 80 | 191 | 18.8 | <0.001 |
Further Information
Wilson's Disease Information Site
Food Standards Agency on Copper
Sample Requirements and Reference Ranges for Copper
| Sample Type | Plasma /serum (fasting sample preferred), urine (24 hour sample)*, liver biopsy |
|---|---|
| Container |
Plasma/serum: Tubes that are trace element free are the preferred sample type but lithium heparin (non-gel) and plain tubes are also accepted.
SST, lithium heparin gel and EDTA (except EDTA tubes that are trace element free) tubes are unsuitable. |
| Precautions |
Plasma/serum: Send by first class post to arrive within 72 hours of collection. If delivery to Glasgow will be outwith 72 hours, separate sample and store plasma/serum frozen until sending and then send by first class post.
|
| Minimum volume** |
Plasma: 250 μL (zinc and selenium can be analysed simultaneously on this volume) Urine: 1 mL Liver biopsy: Ideally samples should have a dry weight >3 mg (multiply by 3.5 to obtain estimated wet weight). Results are increasingly inaccurate when biopsy dry weight is below 3 mg. When the biopsy dry weight is extremely low (<1 mg) the result is likely to be very approximate and should be interpreted with caution. The absolute minimum dry weight that can be analysed is 0.5 mg. |
|
Reference ranges |
Plasma (µmol/L): 10 to 22 (men; STEMDRL derived) Urine copper: < 0.6 µmol/24h (STEMDRL derived)***
Liver: 8 to 40 µg/g dry weight30 diagnostic for Wilson's disease) |
| Mean Turnaround time | Plasma / serum: 2.6 days; urine: 4.5 days (see this page for STEMDRL TAT targets) |
| Method | Inductively coupled plasma mass spectrometry |
| Traceability |
Plasma: Traceable to reference material produced in accordance with EN ISO 17511:2003 “In vitro diagnostic medical devices. Measurement of quantities in biological samples. Metrological traceability of values assigned to calibrators and control materials” Urine: Traceable to reference material produced in accordance with EN ISO 17511:2003 “In vitro diagnostic medical devices. Measurement of quantities in biological samples. Metrological traceability of values assigned to calibrators and control materials” and reference materials with values determined by reference laboratories. Liver: Traceable to certified reference material BCR 185R and ERM – BB186. |
| Intermediate Precision (CV) | See this page for latest data |
| Measurement Uncertainty, U | See this page for latest data |
| Analytical Goals (CV) |
See this page for latest data Plasma copper goal is based on biological variation32,33,34 |
| EQA Scheme | Plasma, urine and liver: UK NEQAS, Guildford (Plasma and urine - once per month; liver - four times per year). |
| Included in UKAS scope? | Plasma, urine and liver: Yes |
* A 24 hour sample is required, unless request is part of a penicillamine test. Please quote volume of timed collection. If a volume is not quoted the sample will be assumed to be random and analysis not performed.
** Absolute minimum volume; this volume is insufficient to carry out repeat analysis if analysis fails.
*** 0.6 µmol/24h is also the cut-off quoted in Wilson’s Disease guidelines.31