Sweat Test Audit

1
Sweat Test Audit

• Steven McCann
• Clinical Biochemist
• Whiston Hospital
• mccann.sjm_at_gmail.com

2
Background

• Cystic Fibrosis
• Prevalence
• CFTR
• Manifestations Lung, GI, Fertility
• Sweat test
• 'that child when kissed on the forehead and
  tastes salty, he is bewitched and soon must die'
  1700's German
• Kessler Andersen 1952 SantAgnese et al 1953
  Gibson and Cooke 1959
• Positive test and clinical history gold
  standard
• Carried out in 180 labs

3
History of the Standards

• 2000 UK NEQAS standing advisory committee (SAC)
  for paediatric tests
• Multidisciplinary group formed
• ACB, British Paediatric Respiratory Society,
  British Thoracic Society, CF Trust, Royal College
  of Paediatrics Child Health, RCPath UK NEQAS
  - various open forums etc
• 2003 evidence based guidelines published

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Audit Guidelines

• rcpch.ac.uk - Evidence based guidelines for the
  performance of the sweat test
• Ann Clin Biochem 20074425-34
• Audit started November 2007 data from Telepath
  covering 1st April 2006 to the 31st March 2007

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Finalised Standards

• Patient information
• Subject suitability
• Sweat collection
• Sweat analysis
• Quality
• Interpretation of results
• Responsibility for testing and training

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Patient Information (3 stds)

• It is good clinical practice to prepare the
  patient and, where appropriate, parent
  effectively before testing
• Not truly audited
• All consultants and respiratory nurse said they
  did provide all patients/parents with Sweat test
  Patient information leaflet. Some parents ask
  the laboratory staff what the test is for...have
  they not been informed?
• ACTION If asked lab staff should re-issue the
  information leaflet and direct queries to the
  paediatric department

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Patient Information (cont)

• Informed consent should be obtained in accordance
  with local policy
• Not audited
• Some Paediatric Consultants stated consent was
  obtained but not usually documented. This should
  be in place
• ACTION At a minimum it should be in the
  patients notes

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Subject suitability (5 Stds)

• All met

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Sweat Collection (31 stds)

• The power supply and electrodes must be regularly
  checked, maintained and recoreds kept
• Electrodes are checked at every test but no
  records kept. Batteries are checked when
  problems arise but no records are kept
• ACTION. This is now logged and signed these in
  the sweat test diary
• Electrical safety of all power supplies must be
  checked annually
• Not currently checked by EBME
• ACTION It is now
• Wescor collectors should be used according to the
  manufacturers instructions, taking precautions to
  avoid direct contact of the sweat-collecting
  surface with the operators hands
• ACTION SOP required clarification for direct hand
  contact with the sweat collection surface

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Sweat analysis (22 stds)

• Liquid sweat from Macroduct collections can be
  stored in sealed Macroduct tubing for upto 72
  hours at 4 degrees. Haematocrit tubes sealed
  with platicine are also suitable, providing an
  air gap is left between the plasticine and sweat
• Any delay in analysis is only upto 6 hours
  Samples are kept at 4ºC until analysis. Analysis
  usually occurs within 2 hours of collection.
  Storage information should be added to SOP
  

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Sweat analysis

• The report should have the date and time of test
  and the date and time of the report printed
• Time of test not included on the report
• ACTION Collection time now added
• The report should have the sweat weight/volume
  collected and minimum weight/volume acceptable
• Actual values not documented on the report
• ACTION Report now contain the weight of sweat
  and adds comment if the weight is low
• Standardised collection time to 30 minutes

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Quality (13 stds)

• Sweat which has been subject to evaporation
  and/or contamination must not be measured
• Not stated in SOP
• ACTION Add to the SOP
• The analytical methods should have a
  between-batch CV of 5 or less at a concentration
  of 40-50 mmol/L
• Mean (95) CV Mean (95)
  CV
• QC l 26.7 (20-34) 13.5 26.8
  (24-29) 3.9
• QC 2 52 (41-63) 10.5 50.3
  (44-57) 6.3
• QC 3 103 (84 -122) 9.2. 100.4 (93-108)
  3.7
• ACTION During audit QC failed now 26/03/08 much
  improved

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Quality

• Results which are not physiological results
  should be questioned (i.e. sodium or chloride
  gt150 mmol/L)
• Not stated in the SOP. Highest result obtained
  in the study period was 101 mmol/L
• ACTION Now modified reportable range lt150
• Failed (i.e. insufficient) sweat collections
  should not exceed 10 of the tested population
  (excluding repeats and tests sick/very young
  patients)
• 84 sweat collections were carried out over the
  year of these 21 (25) were insufficient
• ACTION Emphasise standard required . Review
  equipment and if required retrain failing staff.
  If it looks like a sweat collection is going to
  be insufficient another collection should be
  started immediately

14
Quality

• There should be a repeat target of lt5
• Over the year 06/07 there were 64 patients
  referred for sweat tests. 46 patients or 72 had
  a result reported on the first attempt
• 16 patients (25) had a result reported after 2
  attempts
• 2 patients (3) had a result reported after 3
  attempts
• 1 patient failed to attend for a 3rd appointment
  after 2 failures.
• ACTION With training/new equipment this should
  reduce. Repeat immediately if collection looks
  poor
• Insufficient collections per operator should be
  documented
• Not assessed and difficult to assess
  retrospectively
• ACTION Operator documented in Telepath

15
Quality

• The laboratory should work with clinicians to
  audit sweat test results, in particular repeat
  collections, diagnoses and outcome of positive
  and intermediate results on a regular basis
• Not carried out
• ACTION Retrospectively I wrote to all clinicians
  of patients with results gt40mmol/L to assess
  follow up. All patients were being managed as CF
  (4 results - 51/57, 73, 101 on 3 patients )
• Paeds department were invited to data
  presentation. Apologetically none turned up

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Interpretation of results (7 stds)

• The following definitions are recommended for
  interpretation
• Intermediate chloride concentration of 40-60
  mmol/L is suggestive but not diagnostic of CF
• Chloride 40-60 equivocal please repeat
• ACTION we have now changed our automatic comment
• A sweat chloride of lt40 mmol/L is normal and
  there is a low probability of CF
• Chloride lt40 normal result
• ACTION we have now changed our automatic comment

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Responsibility for testing and training

• A minimum of 10 collection procedures should be
  performed per person per annum
• Not assessed.
• ACTION It is now documented in Telepath for
  future audits
• The responsibilities for sweat testing, both
  collection and analytical, should rest with a
  Consultant (or equivalent) Clinical Chemist and
  should be clearly understood by all operators and
  users a mechanism for reporting any concerns
  about performance should be in place and clearly
  understood
• Overall responsibility lies with Dr Al-Jubouri.
  There have been failures in the past in reporting
  failed sweat collections due to faulty equipment.
  Add to the SOP any failure in service brought to
  the Attention of Dr Al-Jubouri
• ACTION

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Findings

• Majority 75 (50/67) of standards met
• Reporting of sweat weight and time
• High repeat testing rate...equipment failure
• Lack of documentation - equipment and collector
  
• Re-audited after changes
• Everything has improved...

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Impact assessment

• Managed Risk
• Improved practice
• Improved experience
• Better resource use