SESTINI at unisi.it SESTINI at unisi.it
Sat Dec 30 07:32:42 EST 1995

> Date: Sat, 30 Dec 1995 05:29:51 GMT
> Message-ID: <95123002424.~INN-PSCa00202.bionet-news at dl.ac.uk>
> From: Steve Grenard <grenard at herpmed.com>
> Subject: PPD Cross Reactivity

> I am interested in knowing if a patient is mistakenly given two PPD tests,
> perhaps a day or so apart or even a few hours apart, if there can be
> cross-reactivity causing one or both to be a false positive?

A positive PPD reaction may wane over the years. If a subject is tested
repeatedly at this point, the stimulus of the first test can cause the
reaction to reappear or to increase in the subsequent test.
This is called the "booster phenomenon" and may cause such a subject
to be wrongly classified as a recent converter. It is not a false positive
or a cross reaction.

The booster phenomenon occurs more frequently in persons over 55 years,
usually when the test is repeated between 10 days to 12 month or more apart.
I don't know about the short intervals that you asking about.

You can find more information and many references on any good textbook on

Hope this helps

Piersante Sestini

Piersante Sestini   sestini at unisi.it
Istituto di Malattie dell'Apparato Respiratorio
Viale Bracci 3, I-53100 Siena, Italy
Tel +39 (577) 586794/586711   fax +39 (577)280 744

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