[Closed] Question for the Doctors on here (the medical type)

IANAD

It depends what particular tests the GP has ordered. In the case of chronic and unexplained fatigue, if they haven't ruled out anaemia, they might do a full blood count which looks at the levels of various different blood cell types, and check for iron levels (iron is necessary for the manufacture of red blood cells). Perhaps a liver function test too.

The results of these can prompt further investigations if suspicious results are found, although there are relatively benign reasons why cell counts might be lower than expected.

Broadly though, certain findings in the full blood count can indicate that further tests are required, and could reveal hints of certain types of blood cancers etc, but plenty more investigation would be required to confirm this.

There do exist various blood tests for chemicals associated with other common cancer types, but whether the GP would order them as a first thing I don't know.

Normally the form you take in for the blood test will have what the doc is asking the lab to do with the sample - FBC, iron, LFT etc - so it will give you an idea of what they are looking for, or looking to exclude.

If you are unsure of what the doctor is aiming for, you should see if you can have a quick chat to clarify.

I'm not a doctor

But...
There's not a magic blood test for cancer as such, you can look for specific markers for some cancers if suspected, but don't think they're is one for melanoma.
You'd need further tests, maybe for circulating tumour dna, but only if the initial test suggested it.

In the first instance white blood cell, platelet, red blood cell counts and their ratios to each other will give a good idea whether there's some sort cancer that requires further investigation. Certainly that'd ID a blood cancer.

It'd be a full ctc scan to confirm other sorts, but a blood test should give a good idea

Ianad

But, as above.  When it looked like I had cancer I was given a whole raft of tests to check including x-ray, fmri and pet scans but I don't recall specific blood tests.   I think one involved being injected with a slightly radioactive sugar and then scanning with a gamma camera to watch where the sugars were going.  My initial diagnosis came from an x-ray rather than blood tests and in the end they had to operate to check rather than do a blood test

My takeaway was that there isn't a single test that can pick these things up and that they are always looking at a broad range of things to give them the best idea of what the cause might be.  Things may have changed though

Edit: the way it works here as well is that the lab doesn't just test for stuff.  My doctor will ask the lab to test for specific things depending on what she thinks is wrong with me and why.

There is a protocol for "tired all the time" - a series of tests that is the normal bundle.

There are some inflammatory markers that can show up that give a hint there is a cancer but no definitive blood test IIRC

Depending on the results from the first round of tests further tests may be indicated. You wouldn't normally go for CAT scans and the like unless there was some indication

If the blood tests showed vit d deficiency that can take many weeks to correct

the way it works here as well is that the lab doesn’t just test for stuff. My doctor will ask the lab to test for specific things depending on what she thinks is wrong with me and why.

Although certain results will trigger follow on tests and useful information included in the clinical details on a request form could lead to extra tests being added.

I don't work in your local biochemistry or haematology lab though.

There’s not a magic blood test for cancer as such, you can look for specific markers for some cancers if suspected

No help to the OP but one is being trialled at the moment, was on the local BBC news as its being trialled in Derby I think. Initially aimed at adding it to the tests run at your over 50 MOT check up, but presumably of wider use.

Firstly, I hope your lethargy isn’t anything serious…
Secondly, probably 95% of cases of “tired all the time” are simply the extreme end of normal human functioning… i.e MOST people feel tired/lethargic, and I suspect it’s to do with our current lifestyles of doing too much, not eating well, and stress and poor sleep…
I’m not saying this is YOUR case, but it’s an observation..

with regards to blood tests for cancer… essentially the way medicine works is HISTORY (i.e the story from the patient), then TARGETED TESTS…
This is why the American model of “pay for a whole body MRI scan TODAY TODAY TODAY” is pretty useless, as you can pick up all sorts of insignificant things that may never have caused issues, or be unrelated to symptoms (if there are any symptoms).
As an example…there’s no point doing a urinary pregnancy test on ALL patients to see if they are pregnant, because what if I ( a sexy young male) had a test come back positive..would you throw a baby shower for me? It’s more likely the reproductive age female with swollen breasts an no period for 3 months is the pregnant one, not me…
Hence, TARGETED TESTS.

So to answer your question.. “Tired all the time” is a VERY BROAD symptoms, thus the true cause may be stress, depression, thyroid, a cold, alcoholism, poor sleep, cancer, overtraining, new kids…
The initial blood tests will be very broad, as the symptoms are rather ‘loose’.
It’s not fair to say “they won’t test for cancer” because some blood tests (and you should also have a chest XR as well) may show a possibility of a cancer (i.e raised platelets CAN be raised in cancer. They can also be raised with a toenail infection. Hence, HISTORY is key..)

There does exist certain tumour markers, but…they are mostly used for monitoring already known cancers.

The key thing in this situation is to realise how modern primary care medicine works; it’s important to rule out serious and life threatening illness early on. As in your example, the doctor will do enough tests to satisfy themselves that you are VERY UNLIKELY to have cancer or a serious illness. They may NOT actually be able to say “you are tired because of disease X”, but they will be able to say that it’s very unlikely due to a serious illness.

DrP

I am a doctor, a GP. The question is too vague to give a particularly helpful answer but:

1.it depends on the clinical situation. 35 year old who has no specific symptoms, low suspicion of cancer. 85 year old with weight loss, high suspicion of cancer. “tired all the time” is an incredibly common symptom. Mostly we would do full blood count, diabetes. thyroid, kidneys, liver. Maybe vitamin D. As above none of these is a test for cancer specifically. Iron deficiency anaemia on the full blood count would prompt further investigations to rule out bowel cancer in some people (eg above a certain age) for instance

2. The lab do the test that the doctor requests. Perhaps they would have checked that the vitamin deficiency has been reversed? Perhaps they would have checked something different. It’s mainly about symptoms. So retaking the history is more important. Fatigue on its own doesn’t narrow things down. Abdominal pain, weight loss, change of bowel habit, etc might point towards other tests. If they are a smoker maybe a chest x ray especially if a cough or short of breath.

3. There is no blood test that would show melanoma. It’s diagnosed by looking at the skin.

Despite what you might believe about modern medicine, there are only a handful of “blood tests for cancer”
Psa for prostate cancer- so men over 50 with urinary symptoms
Ca125 for ovarian cancer- so for women or a similar age with bloating or vague abdominal pains. Old person with back pain- immunoglobulins for myeloma. None of these is diagnostic without further more invasive confirmatory testing.
There are dozens of different cancers, why would one blood test be able to detect them.

The diagnosis comes mainly from the history (symptoms), and is confirmed by examination and investigations. It’s very rare that a blood test tells us someone has cancer.

My wife has a blood test done a few months ago, it picked up pre-diabetes, low iron, thyroid. It didn't pick up the breast cancer for which she is now being treated.