Blood Sciences Test


Monitoring for potential toxicity in patients with metal on metal hip protheses

Protocol

Sample is a large EDTA tube.

Please note the hip replacement monitoring service is currently only available by referral to the Orthopaedic surgeons at the RDE.

Note MHRA has updated its alert as of June 2012

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While both chromium and cobalt ion levels are elevated in patients with MoM implants, cobalt is the most important contributor to metal ion toxicity. When cobalt was used to treat refractory anaemia in patients in the 1960s, symptoms of cobaltism were described and subsequently confirmed to include neurological, cardiac and endocrine symptoms. Pathology laboratories are reporting an increasing number of people who have had an MoM THR with very high serum cobalt concentration (>1000 nmol/L). Serum reference ranges for cobalt and chromium are 0–20 nmol/L and 0–100 nmol/L, respectively. Patients with high serum cobalt concentrations who undergo revision surgery with ceramic-plastic revisions experience a rapid fall in serum cobalt and significant improvement in neurological and cardiovascular function.

MDA/2010/033: If metal ion levels in whole blood are elevated above 120 nmol/L (cobalt) or 135 nmol/L (chromium) [i.e. seven parts per billion (ppb) for either metal], a second test should be performed three months after the first in order to identify patients who require further surveillance, which may include cross sectional imaging.

Signs of cobalt–chromium toxicity — advice for GPs

Cobalt–chromium toxicity produces a symptom complex that may include neurosensory, endocrine,respiratory, neurocognitive, cardiac and neurological symptoms, such as loss of auditory and visual acuity. When presented with a seemingly disparate cluster of symptoms, it may be difficult to identify metal ion toxicity as a potential precipitating cause, even in people who have had MoM THR.

The essential link between symptoms and peak metal ion levels, or the length of exposure to these ions, remains unclear. Consequently there is a lack of consensus worldwide regarding the safe level of metal ions in the bloodstream, and more research is required to establish the levels at which the presence of metal ions causes toxicity. Many people with MoM THRs and high cobalt levels have fully functioning athroplasties and no signs or symptoms of toxicity.

Current guidelines suggest referring people with a cobalt level > 340 nmol/L, with or without symptoms, to their orthopaedic surgeon. Increasing levels on serial review should also prompt referral to the treating surgeon for further investigation and review.

Referred Test

Analysis performed by Partnership Pathology Services. Frimley park and Royal Surrey County Hospitals NHS Trusts.
Pathology Helpline 01276 604998

 

Specimen Labelling Procedure