Specimen rejection

Occasionally the laboratory has to reject specimens for the following reasons:

  • Unlabelled specimens. (*See below)
  • The request is not for Microbiology.
  • Incomplete request form (no patient details)
  • The details on the specimen and the request form do not match.
  • Insufficient information on the request form to determine the examination required.
  • The sample submitted is unsuitable for the investigation requested.
  • The sample fails to comply with Health and Safety regulations.
  • Leakage or loss of sample due to damaged container.
  • Poor quality of specimen, e.g. sample not fresh, haemolysed
  • Samples of saliva for respiratory culture
  • Solid stool samples (except for ova cysts and parasites)

*Unlabelled Specimens – These will not be processed. Unrepeatable specimens only will be processed following the completion of an “unlabelled specimen” form by a member of the ward staff.

The laboratory will contact the ward/clinician to inform them of rejected specimens, at the discretion of the Laboratory Section Manager. A report will be issued giving the reason for the rejection of the specimen unless there are insufficient details provided to admit the patient onto the system or match with an existing patient.

Specimen quality

The reliability and value of test results depends of numerous factors.  Improper collection, transport or processing of a specimen can affect test performance and the interpretation of results. For example

  • Site of Collection, e.g. For Pertussis infection, a properly taken pernasal swab is essential to ensure recovery of the organism
  • Sample Container, e.g. a urine containing boric acid may not be used for TB culture.
  • Transport Medium e.g. samples for PCR must be sent in viral transport media and not in charcoal-based transport medium
  • Transport Time, i.e. specimens should be transported to the laboratory as soon as possible to increase likelihood of recovering pathogens. See table below for the maximum age of the specimen before it is rejected for being too old to process
  • Transport Temperature – Specimens left at room temperature will become overgrown with normal bacterial flora. Bacteria can multiply at room temperature particularly in urine samples. Therefore it is very important to have the specimens sent to the laboratory straight away or refrigerated in the specimen collection points. (Exceptions include blood culture bottles and genitourinary samples for gonococcal culture –  these should not be refrigerated be transported to the laboratory as soon as possible)
  • Volume of specimen, e.g. blood cultures.
  • Time of Collection, e.g. Samples for culture should, if possible, be taken before antibiotics are started.
  • Poor quality specimens, e.g. blood cultures may be contaminated with skin flora if there is inadequate skin disinfection.
  • Clinical details – in some cases we will only perform certain tests if indicated by the clinical details. Important clinical details include history of foreign travel, recent hospitalisation abroad, occupational factors such as abattoir worker or vet, and vaccination history.

If in any doubt, please contact the laboratory for advice

Specimen Notes Maximum age
Blood cultures 3 days
Urine in (boric acid) 4 days
Urine (not in boric acid) 3 days
Urine TB investigations 3 days refrigerated
Wound swab 3 days
Genital swabs 3 days
Stools 3 days
Clostridium difficile 3 days
Serum N/A (depends on storage)
Mycology Nails N/A
Hair N/A
Skin N/A
Sputum Culture 2 days
TB investigation 3 days
Fluids Ascitic 3 days
Pleural 3 days
Dialysis etc. 3 days
Pus/Tissue At discretion of lab management / consultant
Chlamydia/gonorrhoea Molecular Swab or urine 30 days at 2-30 ºC in Hologic collection tube
IFAT 48 hours @ 4 ºC