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Wellington SCL Newsletter
14th August 2019

Please find the latest information from your laboratory provider Wellington SCL.  In this newsletter we cover:

 
  • Thrombophilia Testing: to do or not to do?
  • Protamine Sulphate Testing
  • Choosing to Test B12 wisely - has it made a difference
  • New strain Chlamydia trachomatis not detected by Hologic Aptima assay

Thrombophilia Testing: to do or not to do?

Despite the increased risk of venous thromboembolism (VTE) associated with inherited thrombophilia, the detection of these inherited abnormalities rarely determines patients’ anticoagulation management. Anticoagulation management is largely determined by the patient’s personal and family history of VTE. International testing guidelines have therefore become more restrictive to reflect this.
 
In general, thrombophilia testing will only be performed outside these guidelines if it will affect patient management or is likely to be informative for future management. Testing outside these guidelines will need to be discussed with and approved by a haematologist.
 
Inherited thrombophilia describes a familial tendency for some individuals to develop venous thrombosis such as deep vein thrombosis (DVT) with or without associated pulmonary embolus (PE). Collectively venous thromboses are now termed Venous Thromboembolic events (VTE). Reduction or deficiency in the natural occurring proteins in the anticoagulation system, Protein C, Protein S and Antithrombin will place an individual at higher risk of venous thrombosis. The Factor V Leiden and Prothrombin (F2G20210A) gene mutations have also been shown to be associated with an increased risk of venous thrombosis.
 
Acquired thrombophilia covers a range of conditions that develop during the lifetime of an individual which result in an increased risk of thrombosis, both venous and arterial. Antiphospholipid syndrome is the most well recognized specific pro-thrombotic syndrome. Antiphospholipid syndrome is diagnosed by the persistent presence of lupus anticoagulant and / or antiphospholipid antibodies and is also associated with an increased risk of miscarriage in pregnant women.

The majority of thrombotic events develop in patients with no recognized specific inherited or acquired prothrombotic tendency.  These events become more common with advancing age, immobility, chronic ill health, obesity, cancer, surgical intervention and use of oestrogen-based contraception or HRT or in pregnancy. For further information on prevention of VTE in this group please follow this link: VTE Prophylaxis Policy
 
Previously thrombophilia testing has been common in unselected patients and their families. However, it has now become apparent that testing for heritable thrombophilia does not predict likelihood of recurrence in unselected patients with symptomatic venous thrombosis (Baglin, et al 2003, Christiansen, et al 2005) and testing for inherited thrombophilia did not reduce recurrence of venous thrombosis in a large cohort study (Coppens, et al 2008). There is a low risk of thrombosis in affected asymptomatic relatives followed prospectively (Langlois and Wells 2003) and the results of thrombophilia tests are frequently misinterpreted (Jennings, et al 2005).
 
Whilst thrombophilia screening is no longer felt to be of value in unselected patients it is helpful for selected patients to receive advice / counselling on measures they can take to prevent VTE themselves. Wellington Hospital therefore holds a doctor/nurse led thrombosis clinic. Patients who are referred to the thrombophilia clinic are seen by a nurse or doctor first to obtain a full thrombosis history, organise targeted thrombophilia screening where appropriate. Patients will be given practical, individual advice on subjects such as future high risk situations, hormonal contraceptives / HRT, travel and pregnancy. This also gives advice or decisions on duration of treatment with anticoagulation.

Click here to view who should have testing

Dr Alwyn D'Souza
Clinical Haematologist 
Wellington SCL

Protamine Sulphate Testing

Our Wellington SCL Haematology department is pleased to announce the introduction of a new test, Protamine Sulphate, which can confirm the presence of heparin contamination in otherwise unexplained prolonged APTTs.

As part of the Coagulation screen, this test will be automatically reflexed if required or can be requested specifically if approved by a Haematologist. This should aid the physician in interpretation of results and most appropriate course of action.

For further information, please contact 

Rebecca O’Toole
rebecca.otoole@wellingtonscl.co.nz 
Haematology Head Department
Wellington SCL

Choosing to Test B12 wisely – Has it made a difference?

Triaging of vitamin B12 requests through éclair e-ordering began in the community in December 2018.  This process supports referrers in selecting the most appropriate setting for testing for Vitamin B12 deficiency in symptomatic patients, and since this process was introduced Vitamin B12 request numbers through all ordering processes have dropped by 44% when compared to the same period last year.  To demonstrate the impact this change has made, we have added the 2019 “post triage introduction” data to the graph from our first Vitamin B12 article last year.

                             
While the impact of this initiative is clearly evident, the detection rate for those patients who are most likely deficient (B12 <110 pmol/L), has remained the same, so we are not missing likely deficient patients through our triaging process.  

The proportion of patients in the borderline range of 110-170 pmol/L have also remained stable at 6%, but interestingly, the number of patients whose values are above the top of the reference interval (>800pmol/L) has increased.  

Closer analysis of those patients who were above the measuring range of the assay (B12 >1476 pmol/L), as well as above the top of the reference intervals showed that 35% of these patients had their test repeated within 6 months of their previous level, so within the recommended minimum repeat interval.  This group included patients with a previously low B12 <110 pmol/L, tested within 6 months of the first level, who now have levels above the reference interval, most likely measuring the supplementation rather than a change in the patient’s Vitamin B12 status, as well as patients whose initial levels were above >800 pmol/L but were still repeated, when an elevated Vitamin B12 does not need either confirming or repeating. 

While the patient groups with results above the top of the reference interval are predominantly in the groups we triage for, levels this high raise the question as to whether these patients are actually symptomatic, or purely patients who are in at risk groups for B12 deficiency.  The most effective use of vitamin B12 testing is in patients groups who are at risk of deficiency, as well as being symptomatic for B12 deficiency.

Overall, we are very pleased with the outcome of this initiative, and will continue to work on ways of making the minimum repeat interval more accessible for requestors, which should also reduce inappropriate testing.

Max Reed
Head of Department, Biochemistry
Wellington SCL


Dr Melissa Yssel
Chemical Pathologist
Wellington SCL 

New strain Chlamydia trachomatis not detected by Hologic Aptima assay

There have been recent reports from Europe of a circulating C. trachomatis variant with a mutation in the 23S rRNA gene allowing it to escape detection by the Aptima Combo 2 CT/NG assay.  This strain accounts for 6-10% of C. trachomatis positive cases in Finland, and has also been detected in a handful of samples in Sweden and Norway. The mutation confers difficulty with detection of chlamydia, but has no effect on antibiotic treatment for the organism. After extensive testing, including over 140,000 samples in the United Kingdom alone, no additional cases have been detected in other European countries at this time.

Given the absence of this mutation outside the Nordic region, it is currently very unlikely that a patient in New Zealand presenting with symptoms of an STI carries a mutant C. trachomatis strain. Therefore, practitioners and patients should be reassured that the excellent overall performance of the AC-2 for the detection of C. trachomatis in your region is unchanged.

Representatives from Healthscope laboratories have spoken to Hologic, the manufacturer, who have advised us of several interventions and surveillance systems that are rapidly being instituted in order to monitor for, and reduce the risk of, false negative results.

The manufacturer is currently in the process of updating the Aptima Combo-2 assay so that it reliably detects the mutants. They aim to make the revised assay available by the end of this year. Additionally, in the short term, a centralised, European surveillance system is being set-up to detect potential spread of the mutant through sexual networks. Informal surveillance will also be performed in the US and Australasia.

In New Zealand, Healthscope laboratories will identify certain samples for which further analysis for mutants will be performed through prospective sentinel clinical and laboratory surveillance. Most of this work will be done based on laboratory parameters, but Clinical Microbiologists will also liaise with sexual health clinics to identify patient groups where additional analysis of tests may be warranted.

The aim of these surveillance activities is to detect potential spread of the mutant strain outside the Nordic countries, in order that, should this occur, appropriate and timely interventions can be performed to mitigate the risk of false negatives in other regions of the world.

We will communicate further as necessary. 
 
Dr Juliet Elvy
Clinical Microbiologist
Wellington SCL 



 
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