Achieving the best lab test results

Always communicate with the pathology lab to ensure the best results, writes Dr Ceridwen Coulson.

Tests are regularly requested by GPs. These may be to help make a diagnosis or to monitor a patient with a chronic condition. To gain the most relevant information for each patient several processes have to come into play. What your pathology lab will strive to provide is 'sample in - intelligence out'.

In order for this to happen, the GP must request the most relevant test; the correct samples need to be taken, into the appropriate tubes, be stored correctly, transported safely, delivered to the lab while analytes are still stable, someone must be there to receive the samples (24 hours a day), and deal with them if urgent, centrifuge and/or store them appropriately.

Someone must request and analyse the required tests correctly then telephone clinically significant abnormal results to someone who can act on the results.

All results need to be communicated back (by paper or electronic transfer) to the correct requester in a timely, efficient way, then assessed by the GP.

Many factors interplay at each of these steps, all of which can add or detract from the value of the process.

To request the most appropriate test depending on clinical scenario and the differential diagnoses, there are laboratory-based websites you can search (see Resources).

If you have a complex situation, telephone your local laboratory for advice.

If you are monitoring a patient with chronic disease there are often local guidelines to follow. If you are requesting an unfamiliar test, check which bottle to use for each sample,what time of day or month to take the sample, and how it should be transported to the lab.

Plasma glucose is only stable in blood with no preservative for about four hours, and serum testosterone is highest in men at about 9am; gonadotrophins are normally best measured on days 1-5 in women with a regular menstrual cycle.

Some analytes are unstable in blood and the sample must be transported rapidly on ice for centrifugation and serum separation.

Consider if a test be would be more informative if done on a patient's urine, blood or other body fluid. Blood samples must be taken in the correct order to avoid contamination. Potassium EDTA (in bottles for FBC) will interfere with several biochemistry tests, for example, so it is best to fill the plain bottle first.

Samples must be labelled correctly with sufficient patient-identifying information or the lab will refuse to accept them. If it is a series of samples from one patient, times must be clear.

Communicate with the lab
With either a paper request or electronic order communications, add some clinical information; it helps the clinical staff in the lab to interpret the test results (e.g. high prolactin in a patient taking an antipsychotic), to ensure the most appropriate reference range is given, and perhaps add appropriate further tests to shed light on the patient's condition.

As an example, some laboratories perform a 'front-line' TSH on all requests for thyroid function, and decide whether or not to add free T4 or free T3 on the basis of the TSH result and the clinical information provided.

This system reduces costs, but its success is dependent on the quality of clinical information given (e.g. 'patient is taking T4 replacement' or 'taking carbimazole').

Urgent tests
Ensure it is clear to whom the report is to be directed. If results are wanted urgently or there is a high chance of significant abnormality, add a contact telephone number. Telephone the lab if analysis is needed urgently, so the staff are warned and look out for the sample among the hundreds received.

You will probably take it for granted that the analytical process delivers an accurate, precise result. However, much effort is expended by the lab to ensure this. Labs all belong to the necessary quality control schemes and performance is carefully monitored. If you perform any tests in your practice by point of care testing you will be aware of at least some of the governance issues.

Laboratories will have 'action limits' for analysis that define when clinically significant results must be telephoned to a clinician or surgery. It is useful if these are developed mutually so you are aware of levels that would lead to an alert. This is particularly important out of hours.

How will you want your patients contacted at these times if they have abnormal test results?

Another area of useful clarification is how you feel about the lab clinical staff adding on further investigations, either by established protocols or in the light of initial test results.

Would you like the decision regarding further investigation passed back to you?

For example, you might be happy for serum electrophoresis to be added to a request for LFTs following a low albumin result and high globulin, especially in a patient with bone pain.

But you might prefer that, if electrophoresis shows a low alpha-1 region, the request for alpha-1 antitrypsin phenotyping is made by you only after discussion with the patient concerned.

The main message is effective communication. Mutually decide with your lab the optimum approach in relevant areas. Perhaps ask a lab member of clinical staff to visit your surgery to discuss areas of concern, controversy, or common and unusual cases.

If you give the lab staff relevant clinical information they will provide you with test results and interpretation in the best way to help you provide excellent patient care.

  • Dr Coulson is consultant chemical pathologist and head of Clinical Biochemistry Services at North Bristol NHS Trust.


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