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Wellington SCL Newsletter -
29th March 2018

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

  • Perplexity around methylphenidate
  • ELab to Éclair Lab Orders Transition in the Wellington & Hutt regions
  • Warfarin Dosing Transition to Wairarapa GPs
  • Key Performance Indicators November 2017 - January 2018
  • Easter Weekend 2018 Collection Centre opening hours 

Perplexity around methylphenidate

  • Monitoring methylphenidate compliance - request urine methylphenidate NOT urine drug screen
  • Positive urine amphetamine is unlikely due to methylphenidate use.
 
Methylphenidate (Ritalin) is a central nervous stimulant that is used for the treatment of Attention Deficit Hyperactivity Disorder. The prescription of the medication has been increased worldwide. It is recognised that laboratory testing play a valuable role in monitoring the compliance. In addition, there can be clinical indications that urine drug screening is required in this group of patients. As methylphenidate has similar pharmacological properties to amphetamines, there is confusions around how methylphenidate can affect the urine amphetamine results.

Methylphenidate and its metabolites is generally not considered to cross-react with amphetamine in the urine immunoassay. The basis of cross reactivity in immunoassay is structural similarity. In spite of sharing similar dopamine-releasing pharmacological actions, methylphenidate is not structurally similar to amphetamine. Furthermore, the manufacturer of the urine amphetamine assay used in our laboratory, Roche Diagnostics, indicated in their document that methylphenidate at 100,000 ug/L in human urine would not give a positive result in their urine amphetamine assay. Although there was a report describing cross reactivity of methylphenidate in amphetamine assays published in 2002, that was the only report in the scientific literature and no similar cases of cross-reactivity have been described since then. In essence, a positive urine amphetamine on immunoassay should not be assumed to be due to the use of methylphenidate. On the other hand, the urine drug screen for amphetamine is also not fit for monitoring patients’ compliance of methylphenidate. 

Targeted analysis for methylphenidate and its major metabolite ritalinic acid in urine is available. The analytical method is liquid chromatography and electrospray ionisation tandem mass spectrometry with isotope-labelled internal standards which is highly specific and sensitive. The result is reported as detected when the drug present in the urine at a concentration of ≥ 5 ug/L. Thus, for compliance monitoring, urine methylphenidate should be requested.

It is imperative to come to the realisation that urine drug screens, namely for amphetamine type substances, benzodiazepines, cannabinoids, cocaine and opiates, by immunoassays should be regarded as screening tests only. Cross-reactivity is a relentless issue for immunoassays. For amphetamines, the potential interferents include chlorprothixene, mexiletine, ranitidine, selegiline, sertraline and this list is not exhaustive. Most of the time, it is indeed not practical to work out what exact interference is causing the false positive results.  On the other hand, unexpected negative results can also happen. For example, benzodiazepine assays do not detect all kinds of benzodiazepines with equal sensitivity. Cannabinoid assays cannot detect synthetic cannabinoids. Hence, it is crucial for referrers to communicate with the laboratory regarding unexpected results on urine drug screening. Confirmatory testing for the urine drug screen results is available on request. This is performed by chromatography with mass spectrometry, which is the definitive method for drug detection.

Dr Carol Siu
Chemical Pathologist,
Wellington SCL

 
References:
Breindahl T, Hindersson P. Methylphenidate is distinguished from amphetamine in drug-of-abuse testing. J Anal Toxicol. 2012:36(7):538-539.
Schwebach A, Ball J. Urine Drug Screening: Minimizing False-Positives and False-Negatives to Optimize Patient Care. US Pharm. 2016;41(8):26-30.
Manzi S,  Law T,  Shannon M.. Methylphenidate produces a false-positive urine amphetamine screen. Pediatric Emergency Care. 2002:18(5):401.
 

Elab to Éclair Lab OrdersTransition in the Wellington & Hutt regions


In readiness for the transition from Elab to the Éclair electronic laboratory request form (in the Wellington and Hutt Valley regions), the Eclair form has been loaded onto your PMS system. You will recently have noticed this form if you have accessed the Wellington SCL icon to view the lab results data repository.  The laboratory form now appears as the default setting. To access the patient results, select the results tab at the bottom of the page.

Please do not be tempted to use this Eclair form until notified, as there are still enhancements to be completed. Fiona James will be in contact with your practice to arrange training when the Éclair form is available.
 

Warfarin Dosing Transition to Wairarapa GPs

 
In early December 2017 warfarin dosing in the Wairarapa transitioned from the lab to some medical centres. The transition went extremely smoothly with very few issues.

The Wairarapa Medical centres using INR Online are reminded to contact INR Online directly with any INR Online queries:
Support is available via INR Online Helpdesk 
9:00am to 5:00pm Monday to Friday
Phone - 0508 WARFARIN (0508 927 327)
Email – help@inronline.net
Or chat window on the INR Online website
 

Key Performance Indicators, November 2017 - January  2018   

 
Wellington SCL's key performance indicators for the period November - January 2018 can be found here 
 

Easter Weekend 2018 Collection Centre opening hours

 
All Collection Centres will be closed on Good Friday, 30th March and Easter Monday 2nd April.

Collection Centres which normally open on Saturday, will be open as usual on Saturday 31st March.  

Click here to view Saturday Collection Centres  
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