## A method of calculating diagnostic indexes for possible cancer symptoms in general practice

##### Permanent lenke

http://hdl.handle.net/10037/12484##### Dato

1990##### Type

Journal articleTidsskriftartikkel

Peer reviewed

##### Forfatter

Holtedahl, Knut Arne##### Sammendrag

Most medical encounters start with the presentation
of symptomns that lead to hypotheses about
the diagnosis. It might be useful to know the probability
of a disease when a symptom of it is presented in
a consulation with a general practitioner, i.e., the
positive predictive value (PPV) of a particular symptom
in relation to a disease. A diagnostic index of this
kind would need to be based on data about symptom
prevalence and disease prevalence in the population
studied, and on sensitivity of the symptom as an indicator
of the disease at the time of the encounter.
Likelihood ratio (LR), the probability of a given
symptom when a particular disease is present divided
by the probability of finding the symptom without
the disease, could also be calculated on the basis of
such data. The calculation of diagnostic indcxes for
colorectal cancer and lung cancer is shown. A Norwegian
general practice study of the seven warning
signals of cancer has yielded data about symptom
prevalence. This material has been combined with information
on local groups of cancer patients, cancer
statistics and population statistics to produce necessary
estimates of cancer prevalence and of sensitivity.
The PPV of the warning signal "indigestion" in relation
to colorectal cancer increases with age from
<0.1 % to2.5%-4.4% for men 70 years old or more.
and 3.4%-6.1% for women in this high age group.
LR varies from 7 to 46 and has slightly lower values
for the highest age groups. For ''cough/hoarseness''
the PPV range for men 60-69 years old is 3.9%-9.0%.
There were insufficient data for males in other
age groups. For women, PPV for the different age
groups varies from 0.1-0.2% to 0.6-1.5%, with
a slight increase with age. LR in the age group 60-69
years is 22-55 for men and 13-30 for women. There
is a slight tendency to lower LR values with increasing
age in women. The value of a quantitative approach to
cancer diagnosis in general practice is considered. Single
symptoms may be a good starting point, but they
rarely furnish a sufficient basis for decisions. The external
validity of the figures is limited because some of
the base estimates may vary with time and from place
to place. However, the changes from one age group to
another and differences between males and females
probably would show limited variation. The method
may serve as an example of a local quantitative approach
to diagnostic thinking in general practice.