People on vegan and plant-based diets often ask me 'how often do I need to get blood tests?' and 'what do I need to test for?'
These are valid questions, and are actually quite difficult to answer in general terms, as your nutrient needs and status depends on a number of factors, such as your gender, your medical history, your stage of life (whether you're planning a pregnancy, for example), or whether you're on any medications. One thing I can't recommend highly enough is forming a relationship with a good GP who knows you and your medical history, as they will be the one who orders and interprets your blood tests.
To begin with, there’s a lot of confusion about which nutrients tested in the blood are actually reflective of your dietary intake and/or the body's stores. As a prime example of this, many people assume that if their calcium levels in their blood are within the range, that their dietary calcium intake is adequate. This is unfortunately untrue, as the body maintains your calcium levels between narrow limits by way of a mechanism known as homeostasis, so if your dietary calcium intake is low, your body will draw on its calcium stores (i.e. the skeleton) in order to maintain calcium levels in the blood. To some extent, other nutrients are subject to this same regulation, including the minerals zinc and magnesium.
So, how often should you have a blood test?
If you’re otherwise fit and healthy, I wouldn’t recommend having a blood test any more frequently than once per year. If you’ve been diagnosed with a condition such as vitamin B12 deficiency or iron deficiency anaemia, your GP will recommend testing more regularly to ensure that the treatment is working.
What to test for:
1. Full blood examination/count
This provides detailed information about your red and white blood cells, and is usually done with all blood tests. It can be used to detect things such as an anaemia caused by iron and vitamin B12 deficiency.
2. Vitamin B12
As this vitamin is only found in animal products (including meat, dairy and fish), it’s absolutely essential that anyone on a plant-based diet ensure they are taking supplemental vitamin B12 on a regular basis (which you can read more about here).
Your GP will order 'total vitamin B12’, and if this test result is low or borderline low (<260pmol/L), the pathologist will also perform an ‘active vitamin B12’ (holotranscobalamin) test, which measures how much of the biologically active form of the vitamin you have in your blood. Serum methylmalonic acid (MMA) and homocysteine (HC) are metabolites which can also be used to assess vitamin B12 status, but these are not covered by Medicare bulk-billing, so you'll need to pay out of pocket if you'd like these tests conducted.
3. Iron studies
Firstly, there is no greater risk of iron deficiency if you’re vegan or vegetarian (in fact, most people on plant-based diets actually get more dietary iron), though people on plant-based diets usually have lower ferritin levels, which is a marker of how much iron is stored in the body.
As low iron is a relatively common problem for women of childbearing age, it's definitely worth keeping an eye on your levels, particularly if you have heavy periods, are a long distance runner, or are feeling tired and depressed.
If you're interested in reading more about iron and plant-based diets, have a read of this post I published earlier in the year on my blog, or this article published in the Medical Journal of Australia in 2012.
4. Vitamin D
Medicare have recently clamped down on 'unnecessary vitamin D testing' (as it was costing them tens of millions of dollars every year), so under new guidelines, only individuals 'at risk' of vitamin D deficiency are eligible for a bulk-billed blood test (e.g. people with Coeliac Disease, Inflammatory Bowel Disease, or a 'chronic lack of sun exposure’, which just sounds like ‘living in Melbourne’ to me, ha ha).
Vitamin D testing is at the discretion of the GP, so ask them if they think it’s medically necessary for you to have your level tested. As I (and the majority of my clients) live in Melbourne, I routinely recommend vitamin D supplements through the cooler months (May-September) anyway, so for some people it makes more sense to just start on a supplement rather than go out and have their levels tested. In saying this, if your levels are very low, you will need a much higher dose of vitamin D than I recommend for the general population to correct the deficiency, so please have a chat with your GP to see what they recommend for you.
Iodine is something I harp on about a LOT about with clients, as it is required for thyroid function and critically important for pregnant and breastfeeding women. Dietary surveys show that Australians get the majority of their iodine from dairy products, which leaves vegans (and some vegetarians) without a decent dietary source. Unfortunately the soil in which we grow plant food in in Australia are depleted in iodine, which means fruit, vegetables, grains and legumes don't contain much iodine. Brown seaweeds (such as arame and wakame) are very rich sources of iodine, but not many people routinely consume them (and there is a risk of getting too much iodine from them, so I don't recommend starting eating them if you haven't grown up doing so, as dramatically increasing your iodine intake can cause problems). In my opinion, the easiest way to ensure you're getting 100% of the RDI for iodine is by taking a daily multivitamin. The simplest way to assess your regular iodine intake is to do a urinary iodine test.
In summary: your GP is the best person to determine whether you need additional tests depending on your health status. For example, if you've been feeling tired and gaining weight, your GP may want to test your thyroid function, as an underactive thyroid gland could be causing those symptoms. Your GP may also want to test your cholesterol levels (depending on your age, and family history of heart disease) or your glucose tolerance if you are at risk of type 2 diabetes.
One final thing: as a dietitian I can’t order blood tests to be bulk-billed through Medicare, so please ask your GP to fill out a pathology request form for you, which you will then present to the pathology collector.