Poustie et al state that there is no computer package available in the United Kingdom
for calculating percentage weight for height (%WFH). This is incorrect
and for many years there has been available just such a package entitled
W4H under the copyright of Great Ormond Street Hospital for Children NHS
Trust. The program can be used on any version of Windows from 3.1
onwards, Excel, and on Psion's. This p...
Poustie et al state that there is no computer package available in the United Kingdom
for calculating percentage weight for height (%WFH). This is incorrect
and for many years there has been available just such a package entitled
W4H under the copyright of Great Ormond Street Hospital for Children NHS
Trust. The program can be used on any version of Windows from 3.1
onwards, Excel, and on Psion's. This program was produced by the Eating
Disorders Research Team at Great Ormond Street but can be purchased from
the address below:
Dr Bryan Lask
Child and Adolescent Eating Disorders Research Team
Department of Psychiatry
Jenner Wing, St George's Hospital Medical School
London SW17 0RE, UK
As I understand the Scientific Method, a statement purporting to be
factual, either in a scientific article or in a discussion with peers,
must be supported by cited evidence that may be publicly examined for its
scientific veracity.
The paper by Heeley et al provides data to illustrate the equivalence of
conductivity and chloride in cystic fibrosis (CF)
diagnosis,[1] and therefore corrob...
As I understand the Scientific Method, a statement purporting to be
factual, either in a scientific article or in a discussion with peers,
must be supported by cited evidence that may be publicly examined for its
scientific veracity.
The paper by Heeley et al provides data to illustrate the equivalence of
conductivity and chloride in cystic fibrosis (CF)
diagnosis,[1] and therefore corroborates the
findings of an earlier clinical trial by Hammond et al.[2] Further, a
statistical comparison of the extensive published sweat chloride data of
Shwachman et al[3] with the conductivity data of Hammond et al shows that the two
are of equal discriminatory power in CF diagnosis.
Despite this evidence, LeGrys has written a document[4] that
contains a number of assertions on this subject and on other aspects of
sweat testing, that are not supported by any published results of original
work of which I am aware. No clinical trial data exist which show that
conductivity should only be used as a screen, that it is in any way
inferior to chloride as a reliable diagnostic discriminator, or that
conductivity readings of 50 mmol/L are positive for CF. LeGrys's call
for more studies on this matter may be seen as an evasion of the true
issue.[5] I suggest that the time has come, albeit belatedly, for her to
substantiate her case, not with opinions, but by providing proper
citations for relevant experimentally-obtained data to support her
contentions in the said document.
In a separate article[6] LeGrys refers to conductivity as a
"qualitative" assay, appearing to infer that it is less reliable than
chloride analysis. The term "quantitative", used in the pad-absorption
method merely indicates that gravimetric means are used to measure the
obtained sweat. It is obvious that this must be done to allow measurement
of chloride concentration since elution of collecting pads is involved.
The conductivity method is unequivocally quantitative because it measures
a solution property in a micro-cell of defined geometry. The inference is
therfore absurd and irrelevant.
LeGrys, in her eLetter,[5] makes the incredible statement that
since sodium is not as reliable as chloride as a discriminator it would
seem "logical" (sic) that because conductivity measures both, the
discriminatory advantage of chloride would be cancelled out. The logic of
this is difficult to comprehend. Increase in sweat chloride due to
functional aberration of the chloride channel must be compensated by
increase of one or another of the available cation species eg, potassium,
sodium or ammonium in order to satisfy the Law of Electrical Equivalence.
Such an increase in chloride will therefore be reflected by a
proportionate increase in the total electrolyte concentration, which is
the basis of analysis by electrical conductivity.
It is regrettable that lack of proper attention to basic scientific
principles has persisted in the NCCLS Guidelines for sweat testing for a
considerable time without correction and has produced increasing confusion
among medical technologists, particularly in the United States. It is
sincerely hoped that the author of this document will see fit to amend it
appropriately by substituting scientific accuracy for prejudice.
References
(1) Heeley ME, Woolf DA, Heeley AF. Indirect measurements of sweat electrolyte concentration in the laboratory diagnosis of cystic fibrosis. Arch Dis Child 2000;82:420-4.
(2) Hammond KB, Turcios NL, Gibson LE. Clinical evaluation of the
macroduct sweat collection system and conductivity analyser in the
diagnosis of cystic fibrosis. J Pediatr 1994;124:255-60.
(3) Webster HL. Sweat conductivity is a valid analysis for cystic
fibrosis diagnosis. Proceedings of the International Conference; Neonatal
Screening for Cystic Fibrosis. Caen, Sept. 10-11, 1998:101-5
(4) Sweat Testing: Sample collection and Quantitative Analysis:
Approved Guideline. National Committee for Clinical Laboratory Standards
(NCCLS) Document C34-A, 1994.
(5) LeGrys VA. Sweat chloride and conductivity. Arch Dis Child [Rapid Response] 17 July 2000.
(6) LeGrys VA. Sweat Testing for the Diagnosis of Cystic Fibrosis; Practical Considerations. J Pediatr 1996;129:892-7.
Cappendijk and Hazebroek (Arch Dis Child 2000;83:64-6) conclude from
their data that "the major factor in delay is suspected gastroenteritis".
Other studies have not given this factor such prominence and the study
population suggests that the Sophia Hospital was acting as a referral
centre: 32 of 78 children whose admission was delayed for 48 hours had
been seen first by a paediatrician, which may i...
Cappendijk and Hazebroek (Arch Dis Child 2000;83:64-6) conclude from
their data that "the major factor in delay is suspected gastroenteritis".
Other studies have not given this factor such prominence and the study
population suggests that the Sophia Hospital was acting as a referral
centre: 32 of 78 children whose admission was delayed for 48 hours had
been seen first by a paediatrician, which may increase the numbers with
suspected gastroenteritis.
In seeking the chief causes of delayed diagnosis it is helpful to
study all children referred to a district hospital from its catchment
area. Jackson in Newcastle found that parental delay over consulting the
family doctor was important and then, in nearly one-third of 311 home
visits, the practitioner did not decide until a second visit that
admission to hospital for ?acute appendicitis was needed.[1] Jackson, a
paediatrician, did not identify gastroenteritis as a factor. Other work
confirms these findings.[2]
In Aberdeen over 300 children are admitted annually from our region
with acute abdominal pain, and have been studied prospectively since 1965.[3, 4] This soon revealed that about one-third had acute appendicitis, one-third progressively settled without treatment (acute non-specific
abdominal pain, or NSAP) and others had medical and surgical conditions.
Among one year's admissions we found that 20 (18%) of 114 children with
proven acute appendicitis complained of diarrhoea compared with 9% of 119
children with NSAP. Of the 20, 15 had rectal tenderness and proved to have
pelvic appendicitis or peritonitis: we emphasised the importance of
identifying, among the many children with gastroenteritis seen by family
doctors, the few who also complain of abdominal pain, who require careful
abdominal and rectal examination.[3] The practice of "Active Observation"
encourages this.[4]
Occasionally delay in diagnosis of appendicitis is seen by the
surgeon on a call to the
isolation ward, where a child has been mistakenly sent in with suspected
gastroenteritis, but this has not, over the years, been a major problem.
Peter F Jones Emeritus Clinical Professor of Surgery University of Aberdeen, UK
References
(1) Jackson RH. Parents, family doctors and acute appendicitis in childhood. BMJ 1963;ii:277- 81.
(2) Moss JG, Barrie JL, Gunn AA. Delay in surgery for acute appendicitis. J R Coll Surg Edin 1985;30:290-3.
(3) Winsey HS, Jones PF. Acute abdominal pain in childhood: analysis of a year's admissions. BMJ 1967;i:653-5.
(4) Driver CP, Youngson GG. Acute abdominal pain in children: a 25-year comparison. Health Bulletin 1995;53:167-72.
Michael Perkin[1] is absolutely right. The initial protocol defined
routine growth monitoring in the setting familiar to us in poorer
countries as three monthly measurements. As we found so few studies in our
first search, we extended the inclusion criteria to any trial where growth
is routinely monitored twice or more in any two year period in children
aged 0-5 years, but neglected to change the wording in t...
Michael Perkin[1] is absolutely right. The initial protocol defined
routine growth monitoring in the setting familiar to us in poorer
countries as three monthly measurements. As we found so few studies in our
first search, we extended the inclusion criteria to any trial where growth
is routinely monitored twice or more in any two year period in children
aged 0-5 years, but neglected to change the wording in the review. We
excluded "single measures at one age"-that is screening policies where all
children at a particular age are measured. However, assuming Hall[2] defines
growth monitoring as "at least two measures in the period 0 to 5 years" we then
sought trials in this area but found none. We thank Dr Perkin for pointing
this out, and will correct the inclusion strategy on the Cochrane Library,
and note the modification to the original protocol. He will note that even
with the wider definition we found no more trials, so the review remains
relevant to both poorer and richer countries.
We thank David Morley for his comments.[3] He notes we did not examine
whether health workers comprehend the growth chart. In fact, we sought
evidence that health workers understood charts and then took action by
seeking studies that recorded referrals (see inclusion criteria). One
study that met the inclusion criteria reported maternal comprehension
following targeted explanations, although it is not entirely clear what
the marks assigned in the test actually mean for the mother or infant. We
would advocate future research examines things that happen as a result of
growth monitoring, such as treatment of intercurrent illness or referral,
rather than what people comprehend about weight charts.
Paul Garner
Ratana Panpanich Stuart Logan
References
(1) Perkin M. Systematic review had no relevance to routine monitoring as it is undertaken in the UK. Arch Dis Child [Rapid Response] 20 May 2000
(2) Hall DMB. Growth monitoring. Arch Dis Child 2000;82:10- 15.
(3) Morley D. Growth monitoring. Arch Dis Child [Rapid Response] 17 July 2000
Zar and colleagues[1] compared home-made spacers and two commercially
available
valved holding chambers (VHCs) for the treatment of children with acute
asthma. We acknowledge that the practice of using empty drink bottles
is common in some countries (by either necessity or choice). We, as a
manufacturer of one of the VHCs that was evaluated, are highly concerned
about the support to the hypothesi...
Zar and colleagues[1] compared home-made spacers and two commercially
available
valved holding chambers (VHCs) for the treatment of children with acute
asthma. We acknowledge that the practice of using empty drink bottles
is common in some countries (by either necessity or choice). We, as a
manufacturer of one of the VHCs that was evaluated, are highly concerned
about the support to the hypothesis that coffee-cup or drink bottle
spacers are as effective as properly designed add-on devices, given by
implication in the Editor's comments on this article (Archives this Month June 2000),
In Zar et al's paper[1] the production technique did not simulate the
release of medication from a
pressurized metered dose inhaler (pMDI). Instead, the technique created
a radiolabelled aerosol by pneumatic nebulization into a bag (which would
have acted as a particle pre-selector). This set-up would not have
reproduced accurately the ballistic component (polydispersed particles)
that is inevitably released at actuation of a pMDI. It has already been
demonstrated that these particles are more effectively separated by a VHC
than a spacer (with no valve). Had a pMDI containing the radiolabelled
aerosol been used (as is the normal practice in gamma-scintigraphic
studies evaluating pMDI systems), we believe that the dynamic aerosol
behavior (inertial impaction of the ballistic component, turbulent
deposition, etc) following actuation into the chamber would have been
quite different to that observed by having patients drawing in the already
formed aerosol from an anesthesia bag. Simply put, the protocol more
closely simulated a continuous jet nebulizer releasing a liquid phase
aerosol into a bag, which was then connected to a chamber/spacer device,
and may therefore have little relevance to what actually occurs inside a
VHC used with a pMDI.
A well designed holding chamber (with a valve) will retain a
significant portion of the coarse component of the emitted dose (particles
greater than about 5 microns aerodynamic diameter) from the pMDI. A
spacer
(home-made or otherwise) will not perform this function effectively.
Rather it will momentarily contain the aerosol and then deliver particles
of all sizes to the well-coordinated patient who is able to time
inhalation with actuation of the pMDI. In the case of corticosteroid,
the emitted coarser particles can promote local topical infections, such
as oral candidiasis as well as increases in overall systemic absorption.
The inhalation valve, that distinguishes a VHC from a spacer,
needs to be a carefully designed component whose function is to retain the
aerosol once created following actuation of the pMDI, then release it
during the inspiratory cycle. Many children, particularly those
suffering an acute exacerbation of asthmatic symptoms, have poor
coordination, and are therefore likely to mistime inhalation with pMDI
actuation. Such patients, who are at greatest risk, are therefore likely
to derive least benefit from the use of home-made spacers.
While we have other observations of a technical nature, the
information given here should be sufficient to provide you with the
message that this study should not be taken as the final word but rather
as a finding concerning the debate about the efficacy of home-made versus
manufactured add-on delivery devices for use in pMDI-based therapy.
Having said this, if a VHC is unavailable for whatever reason, an empty
drinking bottle may be better than nothing at all.
Jolyon P Mitchell PhD, FRSC(UK), CChem
Scientific Director
Medical Aerosol Research Laboratory
Trudell Medical International
Reference
(1) Zar HJ, Weinberg EG, Binns HJ, Gallie F, Mann MD. Lung deposition of
aerosola comparison of different spacers. Arch Dis Child 2000;82:495-8.
As the principal author of the NCCLS guideline on sweat testing
methodology, Dr Le Grys should be better informed of its content. It
includes the clear statement that when sweat test results are obtained by
conductivity measurement "the patient should be referred for quantitative
sweat electrolyte testing". In our paper we refer to this statement as
implying that sweat conductivity measurement should be re...
As the principal author of the NCCLS guideline on sweat testing
methodology, Dr Le Grys should be better informed of its content. It
includes the clear statement that when sweat test results are obtained by
conductivity measurement "the patient should be referred for quantitative
sweat electrolyte testing". In our paper we refer to this statement as
implying that sweat conductivity measurement should be regarded as
"unreliable for diagnostic purposes". This surely cannot be conceived as
misrepresenting the NCCLS position, as claimed by Dr Le Grys. Although the
NCCLS does, by reference, attribute this advice to Cystic Fibrosis Foundation (CFF)(USA) policy, by
including it in their guideline without comment or qualification, the
NCCLS authors are actively promoting it.
The medical politics of the USA do not concern us, but rather the
question as to whether there is any scientific evidence underpinning this
advice which the NCCLS upholds. The result of our study suggests there is
none.
Dr Le Grys quotes research findings (reference 4) which supports the
conclusion that sweat conductivity measurement is appropriate only for
initial screening purposes. We contend that there is no data presented in
this otherwise excellent paper which provides scientific justification for
that conclusion.
Dr Le Grys is of the opinion that the conclusion we draw from our own
study should have been supported by appropriate linear regression and bias
plots of the data. The ADC's professional statistical adviser reviewing
our manuscript, which included such data analysis, thought otherwise and
requested us to remove it.
It is rather ironic that Dr Le Grys should now be pleading for more
studies to be carried out to resolve the issue of the diagnostic
equivalence of indirect and direct sweat electrolyte measurement, focusing
on patients who produce results which are equivocal. Considering the
relative rarity of such patients in general paediatric practice, if the
problem revolves around these cases why did the NCCLS guideline not
clearly state this in the first place? In reality, the final diagnosis of
CF in these cases is likely to be resolved by the results of
investigations other than the sweat test.
I am grateful to Dr Waterston for his commentary. In order to
clarify the issues that he raised, I will confirm the following:
(1) I was suggesting that the practice in all branches of tertiary
paediatrics should be considered as a disability service from the
perspective of the family and child’s predicament. I was not confining
the proposal to traditional neurodisability.
I am grateful to Dr Waterston for his commentary. In order to
clarify the issues that he raised, I will confirm the following:
(1) I was suggesting that the practice in all branches of tertiary
paediatrics should be considered as a disability service from the
perspective of the family and child’s predicament. I was not confining
the proposal to traditional neurodisability.
(2) I was indeed specifically proposing to change the ethos of
hospital services.
(3) My consultation has been with a number of support groups which are
part of Contact a Family.
(4) I have no problem with supporting community paediatrics, providing
we are clear what it is and that it is appropriately resourced, but this
is another issue.
(5) I have no problem about supporting a community based approach to
the whole of paediatrics and have worked with research groups in India,
Bangladesh and Kenya on community based rehabilitation. Whether community
paediatrics as presently practised meets the definition of being a process
which enables disabled people and their families to function and
participate fully within their community and support the primacy of the
community in the use of resources is open to question, as Dr. Waterston I
think agrees. This process would require facilitation of a bottom up
approach, ie, giving power and resources from health, education and
social services to the community, and the research testing of such models.
I was proposing a much more confined revolution of tertiary medicine which
let the users and community into the action reorganising the difficulties
and influence that the people in tertiary services face.
Brian G R Neville
Professor of Paediatric Neurology
The article from the Netherlands by Cappendijk and Hazebroek[1] has again confirmed what is already known in clinical
practice. A recent paper from the Leicester Royal infirmary[2] is almost
identical.
As the authors pointed out, the factors determining the diagnostic
delay are numerous and often cannot be influenced. However, I agree with
their statement that “in a child with abdominal pai...
The article from the Netherlands by Cappendijk and Hazebroek[1] has again confirmed what is already known in clinical
practice. A recent paper from the Leicester Royal infirmary[2] is almost
identical.
As the authors pointed out, the factors determining the diagnostic
delay are numerous and often cannot be influenced. However, I agree with
their statement that “in a child with abdominal pain which do not settle
quickly, appendicitis should be excluded by early and if necessary
repeated surgical consultations”.[1]
The vermiform appendix varies from 2 cm to 24 cm in length, the
average being about 9 cm. It is longer in the child than in the adult. The
position of the appendix shows a high variation in children. [3, 4] This
variation in the location of the appendix in the abdomen explains the
variation of symptoms seen with acute appendicitis. If the appendix is
retrocaecal or located in the posterior portion of the abdomen,
localisation of the pain and tenderness on examination occur late if at
all. If the appendix is posterior in the pelvis, the pain may localise
only to the lower abdomen. And tenderness to palpation is poorly
localised. The diarrhoea of appendicitis is most common in patients with a
low-lying appendix in proximity to the colon and rectum.[5]
We recently saw a 9-year-old boy presenting with maximum tenderness
in the left iliac fossa. There was a 31-hour history of generalised
abdominal pain followed by vomiting. He was referred to the surgeon with
the diagnosis of generalised peritonitis. Examination under anaesthesia
revealed a mass in the left iliac fossa. Laparotomy confirmed a
generalised peritonitis resulting from a left iliac fossa abscess. This
was from a ruptured appendix, the tip of which was in the left iliac
fossa.
References
(1) Cappendijk VC, Hazebroek FWJ. The impact of diagnostic delay on
the course of acute appendicitis. Arch Dis Child 2000;83:64-6
(2) Williams N, Bello M. Perforation rate relates to delayed presentation
in childhood acute appendicitis. J R Coll Surg Edin 1998;43: 101-2
(3) Bakheit MA, Warille AA. Anomalies of the vermiform appendix and
prevalence of acute appendicitis in Khartoum. East Afr Med J 1999;76:338-40
(4) Johnston TB, Whillis J. Gray’s Anatomy 1942; 28th Edition, Longmans,
Green and Co.
(5) Shandling B, Fallis JC. Acute appendicitis. In Nelson’s Textbook of
Paediatrics. 1992; 14th Edition, Behrman R. W.B. Saunders Company
Dr Stephen Kwame Dotse
115 Nab Wood Drive
Shipley, West Yorkshire BD18 4AP, UK
If sleep studeis are worth doing, they are worth doing well. The study of
sleep disordered breathing is another area of paediatrics that the UK has
stumbled to embrace.[1, 2] Sleep medicine has exponentially increased in
adults in recent years, yet in paediatrics many questions remain
unanswered.
While, van Someren et al made a valiant attempt to answer an
important question,[3] they did...
If sleep studeis are worth doing, they are worth doing well. The study of
sleep disordered breathing is another area of paediatrics that the UK has
stumbled to embrace.[1, 2] Sleep medicine has exponentially increased in
adults in recent years, yet in paediatrics many questions remain
unanswered.
While, van Someren et al made a valiant attempt to answer an
important question,[3] they did so by assessing clinical scores in
relation to a standard which was far from gold, and as such accuracy could
not be determined, only inferred. Clinical scores or simple oximetery are
limited in their ability to identify obstructive sleep apnoea (OSA), being
able to identify significant OSA but not mild/moderate cases.[4, 5] Data
is now accumulating that even mild OSA may be associated with significant
neurocognitive morbidity in children.[6, 7] Full polysomnography is the
current gold standard. The Visilab has not been satisfactorily validated
against full polysomnography, and the results presented in the paper
demonstrated a discrepancy in 2 of 10 simultaneous recordings (a 20% error
rate) with important differences in mean oxygen saturation between the two
systems (93% vs 95%). It is true that full polysomnography may not be
required in all children for the diagnosis of OSA, however this process
should be one of working down from a gold standard rather than edging up
towards it. The arguments used by van Someren against the use of full
polysomnography are weak. Children in dedicated sleep areas tolerate full
polysomnography well: In the 54 full polysomnographic OSA studies
performed in the past 6 months in this unit, sleep efficiency was a mean
of 90% (sd 8%), which includes children with frequent wakening as a result
of their OSA!
Centres in both North America and Australia have dedicated
significant funding in recent years to paediatric sleep laboratories and
the appropriate training of both nursing and medical staff through
specific specialist training criteria; the UK sadly lacks such support.
With the exception of one paediatric unit (concentrating on sleep in rare
disorders) sleep related research in the UK is linked to adults centres.
UK paediatrics needs a sleep medicine wake up call, so that standards can
be set from gold.
Steve Cunningham Margaret Harris Consultants in Paediatric Respiratory Medicine
Department of Paediatric Respiratory and Sleep Medicine Mater
Children’s Hospital Brisbane, Australia
References
(1) Shann F. Australian view of paediatric intensive care in Britain.
Lancet 1993;342:68.
(2) Wheeler R, Foote K. Pectus excavatum: studiously ignored in the
United Kingdom? Arch Dis Child 2000;82:187-8.
(3) van Someren V, Burmeister M, Alusi G, Lane R. Are sleep studies
worth doing? Arch Dis Child 2000;83:76-81.
(4) Carroll JL, McColley SA, Marcus CL, Curtis C, Loughlin GM.
Inability of clinical history to distinguish primary snoring from
obstructive sleep apnea syndrome in children. Chest 1995;108:610-8.
(5) Brouilette RT, Morielli A, Leimanis A, Waters KA, Luciano R,
Ducharme FM. Nocturnal pulse oximetry as an abbreviated testing modality
for pediatric obstructive sleep apnea. Pediatrics 2000;105:405-12.
(6) Kennedy D. Neurocognitive function in childhood obstructive sleep
apnoea syndrome (OSAS). 6th World Congress on Sleep Apnea. March 2000;
Sydney, Australia.
(7) Ali NJ, Pitson D, Stradling JR. Sleep disordered breathing: effects
of adenotonsillectomy on behaviour and psychological functioning. Eur J
Pediatr 1996;155:56-62.
As a principal author of the sweat testing document published by
National Committee for Clinical Laboratory Standards (NCCLS) and
consultant to the Cystic Fibrosis Foundation (CFF)(US), I write to address
an inaccuracy in the article by Heeley et al (Indirect
measurement of sweat electrolyte concentration in the laboratory diagnosis of cystic fibrosis. Arch Dis Child 2000;82:420-4). The authors
misrepresent...
As a principal author of the sweat testing document published by
National Committee for Clinical Laboratory Standards (NCCLS) and
consultant to the Cystic Fibrosis Foundation (CFF)(US), I write to address
an inaccuracy in the article by Heeley et al (Indirect
measurement of sweat electrolyte concentration in the laboratory diagnosis of cystic fibrosis. Arch Dis Child 2000;82:420-4). The authors
misrepresent the NCCLS document on the role of conductivity analysis.
Nowhere does the NCCLS document refer to the current conductivity methods
described in the paper as unreliable; it does restate the widely accepted
fact that some older conductivity methods are subject to evaporation
error. The NCCLS document goes on to state that the CFF has approved the
use of newer conductivity analyzers for the screening of CF at community
hospitals, using a decision level of 50 mmol/L.[1] This decision level is
supported by the data presented in the Heeley article. The data presented
in the article concerning equivocal patients also supports the US
reference interval for sweat chloride as normal below 40 mmol/L.[2, 3]
Patients with chloride values greater than 40 mmol/L should be further
evaluated.
The reluctance of many to accept the use of sweat conductivity in
place of sweat chloride for confirming a diagnosis of CF is based on the
fact that chloride determinations directly reflect the genetic mutation of
the disease. Conductivity is a property of all the charged species in a
sample (i.e. sodium, potassium, chloride, lactate, bicarbonate, etc). As
the authors' point out, chloride provides greater discrimination than
sweat sodium i.e. less overlap between diagnostic categories. It would
seem logical then, that combining sodium with chloride in a conductivity
measurement would effectively cancel out the discrimination advantage of
chloride alone. Referring to the data presented in Table 2, there were
twice as many patients with equivocal conductivity concentrations as with
chloride (albeit a very limited sample size). Additionally, there exists
a paucity of data in the scientific literature comparing conductivity and
chloride values in CF and non-CF individuals. Even the scientists
publishing such research support the conclusion that conductivity is
appropriate for initial screening and chloride for confirmatory diagnosis.[4]
Heeley et al's article attempts to provide relevant data, however it is
most unfortunate that the authors failed to include in their analysis, a
linear regression plot of chloride versus conductivity along with a bias
plot of the data so that the reader could assess the correlation. More
studies need to be published comparing conductivity with chloride,
particularly in patients with results in the equivocal range, before the
conclusion can be made that sweat conductivity is as effective as chloride
measurement for the diagnosis of CF.
Sincerely
Vicky A. LeGrys, Dr.A.
Professor, Division of Clinical Laboratory Science
School of Medicine, University of North Carolina at Chapel Hill
References
(1) Sweat Testing: Sample Collection and Quantitative Analysis; Approved Guideline. National Committee for Clinical Laboratory Standards (NCCLS) Document C34-A, 1994.
(2) Rosenstein BJ, Cutting GR: The diagnosis of cystic fibrosis: A
consensus statement. J Pediatr 1998;132:589-95.
(3) Farrell PM, Koscik RE: Sweat chloride concentrations in infants
homozygous or heterozygous for delta 508 cystic fibrosis. Pediatrics
1996;97:524-8.
(4) Hammond KB, Turcios NL, Gibson LE: Clinical evaluation of the
macroduct sweat collection system and conductivity analyzer in the
diagnosis of cystic fibrosis. J Pediatr 1994;124:255-60.
Poustie et al state that there is no computer package available in the United Kingdom for calculating percentage weight for height (%WFH). This is incorrect and for many years there has been available just such a package entitled W4H under the copyright of Great Ormond Street Hospital for Children NHS Trust. The program can be used on any version of Windows from 3.1 onwards, Excel, and on Psion's. This p...
Dear Editor
As I understand the Scientific Method, a statement purporting to be factual, either in a scientific article or in a discussion with peers, must be supported by cited evidence that may be publicly examined for its scientific veracity.
The paper by Heeley et al provides data to illustrate the equivalence of conductivity and chloride in cystic fibrosis (CF) diagnosis,[1] and therefore corrob...
Dear Editor
Cappendijk and Hazebroek (Arch Dis Child 2000;83:64-6) conclude from their data that "the major factor in delay is suspected gastroenteritis". Other studies have not given this factor such prominence and the study population suggests that the Sophia Hospital was acting as a referral centre: 32 of 78 children whose admission was delayed for 48 hours had been seen first by a paediatrician, which may i...
Michael Perkin[1] is absolutely right. The initial protocol defined routine growth monitoring in the setting familiar to us in poorer countries as three monthly measurements. As we found so few studies in our first search, we extended the inclusion criteria to any trial where growth is routinely monitored twice or more in any two year period in children aged 0-5 years, but neglected to change the wording in t...
Dear Editor:
Zar and colleagues[1] compared home-made spacers and two commercially available valved holding chambers (VHCs) for the treatment of children with acute asthma. We acknowledge that the practice of using empty drink bottles is common in some countries (by either necessity or choice). We, as a manufacturer of one of the VHCs that was evaluated, are highly concerned about the support to the hypothesi...
As the principal author of the NCCLS guideline on sweat testing methodology, Dr Le Grys should be better informed of its content. It includes the clear statement that when sweat test results are obtained by conductivity measurement "the patient should be referred for quantitative sweat electrolyte testing". In our paper we refer to this statement as implying that sweat conductivity measurement should be re...
Dear Editor:
I am grateful to Dr Waterston for his commentary. In order to clarify the issues that he raised, I will confirm the following:
(1) I was suggesting that the practice in all branches of tertiary paediatrics should be considered as a disability service from the perspective of the family and child’s predicament. I was not confining the proposal to traditional neurodisability.
(2)...
Dear Editor
The article from the Netherlands by Cappendijk and Hazebroek[1] has again confirmed what is already known in clinical practice. A recent paper from the Leicester Royal infirmary[2] is almost identical.
As the authors pointed out, the factors determining the diagnostic delay are numerous and often cannot be influenced. However, I agree with their statement that “in a child with abdominal pai...
Dear Editor:
If sleep studeis are worth doing, they are worth doing well. The study of sleep disordered breathing is another area of paediatrics that the UK has stumbled to embrace.[1, 2] Sleep medicine has exponentially increased in adults in recent years, yet in paediatrics many questions remain unanswered.
While, van Someren et al made a valiant attempt to answer an important question,[3] they did...
As a principal author of the sweat testing document published by National Committee for Clinical Laboratory Standards (NCCLS) and consultant to the Cystic Fibrosis Foundation (CFF)(US), I write to address an inaccuracy in the article by Heeley et al (Indirect measurement of sweat electrolyte concentration in the laboratory diagnosis of cystic fibrosis. Arch Dis Child 2000;82:420-4). The authors misrepresent...
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