What?
I honestly feel completely out of my depth when it comes to ordering blood tests. My only experience up to this point involves ordering medication monitoring tests (i.e. for methotrexate, renal tests, liver tests and full blood counts should be done at least 3 monthly), and that ESR and CRP are raised in infection/inflammation. This means at least I am familiar with some of the abbreviations, but I don't really understand how to relate blood test ordering to MSK care.
So what?
Ordering appropriate blood test has direct relevance to MSK care in certain contexts, such as for gout, PMR or osteoporosis, although I would not feel confident with which tests to order at what time intervals, and how to interpret their results.
More importantly, being able to order appropriate blood tests will result in a meaningful clinical contact with service users who have been incorrectly triaged and do not actually have an MSK problem. This does not happen infrequently, such as with polyarthralgias, or with people who have red flag signs on questioning. At the moment, all I feel I can do for these service users is to refer them on in the correct direction. If I was able to order some appropriate blood tests whilst they were waiting to see whoever I had referred them to, this would mean incurring less wait time for the service user, and reducing the number of clinical contacts needed before they were able to start appropriate management.
For these reasons, I would like to increase my confidence in being able to order the right tests at the right time, and be able to interpret their results to a level of "does this change my management plan" or "does this change the referral pathway". I don't think it is appropriate for me to be arriving at clinical diagnoses based of the results of blood tests for non-MSK cases.
Now what?
I wanted to address this gap in my knowledge by attending an MACP run course on "de-mystifying" blood tests in FCP.
During the course I realised that I had been focussing too much on what tests to order, and that I wasn't really thinking about why I was ordering them. It helped me move from thinking, "this patient is tired all the time, I must order x y and z" to thinking "this patient is tired all the time, maybe they have undiagnosed diabetes, hypothyroidism, or vitamin deficiency?". This helps to eliminate the "shotgun" approach and order tests that aren't relevant. There are also clinical implications to this, particularly in the case of incidental findings that may not be clinically relevant. Significant delays could be incurred in accessing the correct care, if a patient is diagnosed and treated for a vitamin deficiency, because the clinician had missed thyroid tests off their initial shotgun panel and therefore missed their Grave's disease.
Thinking in this way also helped me to realise that as a rule of thumb, I shouldn't be ordering blood tests if I don't understand how to interpret them. Again, this is not to such a level as to make a clinical diagnosis, but it is to the level of knowing if the results of the blood test will change the management strategy or referral pathway. An example of this could be for gout. A patient may have classical features of an acute gout attack, be sent for a uric acid blood test, and come back with a normal result. This presents the requesting clinician with an issue: do you recommend gout treatment, or do you consider an alternative diagnosis? The truth is that the clinician should not be ordering blood tests if they are likely to get "stuck" if the results aren't as expected. In the case of gout, uric acid levels often do not rise until weeks after an acute flare, so clinicians should be referring for uric acid blood tests more as a qualitative measure rather than a diagnostic one, and treat for the gout empirically given that clinical signs are a much more diagnostically relevant.
The course also gave me some excellent clinical pearls, such as that ESR increases with age and is actually measured in age and sex specific ratios rather an as absolutely numbers, that patients with sarcoidosis can't have vitamin D supplementation as it can make them very unwell, and that PSA can be catastrophically elevated during a UTI!
Overall, I feel much more confident in being able to order relevant bloods, however, I must remain mindful of what the clinical value of doing so might be, both diagnostically (why am I ordering them?) and interpretively (will the results change the outcome?)