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Reliability of self reported smoking status by pregnant women for estimating smoking prevalence: a retrospective, cross sectional study

BMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b4347 (Published 30 October 2009) Cite this as: BMJ 2009;339:b4347

Point of care cotinine testing in pregnancy

Shipton et al (BMJ 29th October 2009) have once again highlighted the
problem of the unreliability of self reported smoking status by pregnant
women. They used stored blood samples and measured serum cotinine to
identify true smokers. This reinforces the need for biochemical
verification of smoking habit to identify all smokers, who can then be
offered advice and support to quit.

Some years ago, while evaluating a novel 5-minute point-of-care urine
test for cotinine and the other nicotine metabolites called SmokeScreen, I
attended two hospital antenatal clinics in Birmingham and gathered
information about smoking-habit from 800+ pregnant women at their
‘booking’ visit. The women were interviewed about 5 minutes after they had
completed their interview with the midwife. They were aware that a
biochemical test for smoking would be carried out. With subsequent
reference to their ‘notes’ we found that 10.3% had denied smoking to the
midwife and 38.4%, although they had reported smoking, had significantly
under-reported their cigarette consumption; only 51.3% reported the same
to both parties (1).

This study demonstrated that cotinine measurements could be carried
out rapidly and easily in an antenatal setting and repeat measurements
were carried out at subsequent appointments to monitor changes to smoking
behaviour following advice to quit. The rapid colorimetric test result (a
positive sample for cotinine turning shades of pink) was shown to the
smoker along with the quantitative result. This feedback was shown to
double the quit rate and increase birth weight (2).

Very few pregnant smokers appreciate why quitting smoking is
important. Firstly, they are weary of constant bombardment of the anti-
smoking message, and ‘switch off’. Secondly, they don’t appreciate that
the chemicals they inhale from tobacco actually get into their blood
stream, and so to their developing foetus. This information coupled with
personalized results throughout pregnancy reiterates the message and
improves smoking cessation, especially in the last trimester.

A subsequent project carried out by community midwives using
SmokeScreen, carried out in the homes of pregnant women, found the rate of
smoking to be an alarming 47%, much higher than the 17% officially
reported for the same population. Furthermore, 75% of the midwives thought
the test motivated the women to stop smoking, 67% felt the test enriched
their anti-smoking intervention and over half thought the test should be
introduced as a routine screen in the early stages of pregnancy (3).

Biochemically-verified information is therefore required during
pregnancy. CO monitoring is one approach, but it is prone to false
positives from environmental sources and the short half-life of
carboxyhaemoglobin allows a short abstinence from smoking (e.g. overnight)
to give a negative result. The point-of-care SmokeScreen test monitors
smoking behaviour for up to three days and allows for quick and simple
cotinine monitoring, and on a urine sample that is routinely brought to
clinic and so removing further patient involvement.

References

1. Cope GF, Nayyar P, Holder R. Measurement of nicotine intake in
pregnant women - association to changes in blood cell count. Nic Tob Res
2001; 3: 119-122.

2. Cope GF, Nayyar P, Holder R. Feedback from a point-of-care test
for nicotine intake to reduce smoking during pregnancy. Ann Clin Biochem
2003; 40: 674-679.

3. Giles J, Taylor D, Cope GF. Incorporation of a point-of-care
cotinine test into routine community care to reduce smoking in pregnancy –
a pilot study. Eur Conf Tob or Health, Basel, Switzerland Oct 2007.

Competing interests:
Dr Cope is the inventor of the SmokeScreen tests and is a director of GFC Diagnostics Ltd, (grahamcope@gfcdiagnostics.co.uk) the manufacturer and distributor of the test.

Competing interests: No competing interests

05 November 2009
Graham F. Cope
Honorary Senior Research Fellow
University of Birmingham, UK