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Add On Tests

We are aware that on occasion it is necessary to request additional tests for a sample already in the laboratory.

Most tests are stable, and may be added to a properly stored sample (see below for sample retention times.) Some are more labile and may not be added on outside certain time intervals.

We will accommodate additional requests where possible, provided that:

There are 2 main methods by which additional tests may be requested:

Information required for all requests is as follows:

Sample retention times:

Specimens are retained in the laboratory for a defined length of time in line with guidance from the Royal College of Pathologists (RCPath.)

Specimens sent for bacteriological culture may deteriorate over time. If the delay to add-on test is greater than 48 hours after the specimen has been received in the laboratory it is preferable to take another sample if possible.

Sample Type Retention Period
Swabs for MC&S 7 days
Tissues/Fluids/CSF for MC&S 6 weeks
Urines for Culture 72 hours
Respiratory Samples for MC&S 7 days
Faeces for Culture 7 days

(For C.diff testing – samples must be less than 72hrs old – to avoid false negatives due to sample degradation.)

Routine Serology Bloods 6 months
Antenatal Serology Bloods 2 years
Donor Serology Bloods 10 years
Swabs & Urines for Chlamydia/Gonorrhoea PCR 72 hrs
Respiratory PCR Swabs 72 hrs
Swabs for HSV/VZV PCR 7 days
Bloods for BK/CMV/EBV PCR 2 weeks
Bloods for HBC/HCV/HIV PCR Plasma/Serum Aliquots kept for 4 weeks
Faeces for Molecular Tests (e.g. Norovirus) 48hrs


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