Tag Archives: Microbiological sampling

“A Site for Sore Eyes”

It is not just the clinical details that are important in how a microbiology sample is worked up. It is also where the sample was taken from, as you will be perfectly aware.

However sometimes the site labelling can be a bit too “generic”.

For example an “ear swab” could potentially mean a swab from the auditory canal (i.e. in someone with otitis externae), or it could mean a swab from the skin on the outer ear (i.e. in a patient with impetigo lesions).

The same can apply to “nose swab”. This could mean the skin covering the outer nose as opposed to the inner nose or nostril.

As a final example a “penile swab” could mean a swab from the urethra or it could mean the skin on the outside of the penis.

and there are others.

But why does this matter?

You have probably worked this out already. The microbiological work up from the two different options on each “site” is completely different. We are looking for different microbes, using different media or tests, and even the reporting procedure, susceptibility testing and comments are all different.

It is therefore critical that the requestors (and sample takers as these are not always one and the same) are educated to be as specific as possible when describing the sampling site e.g. outer ear, ear canal, nostril, outer nose, urethra, penile skin, so that the scientist is in no doubt as to where the sample has been taken from so that correct processing can take place. The education needs to also explain why it is so important from a lab perspective.

Another solution is to define the sites in detail as tick boxes on the request form, but tick box request forms have their own set of problems….

The more useful the information that comes into the lab, the more useful the result is to the patient.


“Dubious Reasons for Microbiological Sampling”

We would like to think that every sample that comes into the microbiological laboratory is of great importance and has been taken for the right reasons. However having been in the business for several years now I know that this is not always the case. Here are some of the dubious reasons that I have come across for taking microbiological samples (most of which can of course can be applied to laboratory investigations in general)

  • To make the patient feel that something useful has come from the consultation: Particularly common in the General Practice setting. The GP may use either a prescription or a laboratory test to demonstrate that he is doing something useful for the patient. Particularly common where the patient is required to pay a fee for the consultation.
  •  Fear: The clinician may order the investigation as there is a fear that he/she may get into trouble for missing something strange or unusual. Also in the hospital setting a junior doctor may order a laboratory test “just in case” the consultant is looking for the result on the ward round.
  •  As a test of cure: Common particularly with regards to urine samples. However laboratory test of cures only very rarely indicated. Most of the time the disappearance of symptoms from the patient is an adequate test of cure.
  •  Temptation: Sometimes wound lesions “are just asking” for a swab to be put into them! A burst boil, a discharging ear, a non-healing venous ulcer. Sometimes the temptation to sample is just too much…
  •  Self-Justification: The clinician may start the patient on empirical treatment and then sample in order to justify the treatment, even though in many cases there is little chance of the sample result actually changing the treatment.
  •  Patient request: The patient who presents to the clinician and demands for a urine sample or similar to be sent to the lab even though the doctor may not think the investigation is necessary and communication of this fact may be more hastle than it’s worth.

There may of course be other reasons which I have not thought of. I suspect however the above list may well make up a significant proportion of the total number of specimens coming into a clinical microbiology department.

If your laboratory is funded on a “fee per test” basis, then you may not care why the sample has been taken. “The more tests the better” for this type of set-up.

However if your laboratory is funded on a capped budget” (probably the majority of labs) then you might want to look more closely at the factors influencing testing to ensure that the most important reason is being considered first and foremost; “Will the result of this test/swab/urine etc have a significant chance of affecting the ongoing management of the patient…”