Blood tests & hot weather: What you need to know
In a world where thousands of (at-home) blood tests are sold direct to consumers, it’s worth pausing before clicking “buy”.
While these tests can seem like a quick and convenient way to check your health markers, there are several important factors to consider before investing in a blood test.
This is true at any time of year, but especially during a heatwave.
Here’s why…
Hot weather can affect blood test results in two ways.
- Heat exposure during sample transport and storage can impact the quality of the sample…
- …while dehydration can alter some of your blood markers.
Heat exposure and dehydration can lead to sample rejection by the lab or affect the reliability of your test results in that they may not accurately reflect your true health status.
How well hydrated (or not) you are matters a lot!
When you’re having a blood test with your GP or privately, don’t forget to hydrate!
This is particularly important during the summer and in a heatwave.
Drinking plenty of water in the days before your appointment (not just on the day itself) helps maintain blood volume and makes your veins easier to find and access.
The result?
A smoother, quicker blood draw and a more pleasant experience for both you and the phlebotomist.
Furthermore, some markers, such as some red blood cell markers, kidney function markers, electrolytes and lipid markers, can be falsely elevated due to dehydration.
Read here how to stay well hydrated.
Blood samples degrade quickly.
In an ideal world, samples should be analysed immediately after the blood draw because they degrade quickly.
This is not always practical and is not possible when samples need to be sent to the lab.
Posting is a common way of sending samples for direct-to-consumers tests back to the lab, and this is also how the lab I use will receive your samples if you work with me, and if the samples sit in a hot post box during summer, the degradation is even quicker.
Hence it’s always advised to post any at-home samples via Special Delivery to ensure the sample reaches the laboratory as quickly as possible and remains as stable as possible during transit.
Also avoid having a blood draw close to the weekend when the postal services are maybe slower and the samples would arrive at the lab during the weekend when the lab might be closed.
A blood test is only as useful as the sample quality and the way the results are interpreted.
When my clients run any blood testing (or any functional testing) with me, I provide detailed instructions and support them through the process — from preparing for the test to making sure the sample is collected and handled correctly.
Buying a test kit online can feel simple, but without personalised guidance you may miss important steps that can affect the quality and usefulness of your results.
Think twice when ordering a finger-prick test.
I generally advise against finger-prick testing for panels that require more than a few drops of blood.
Collecting sufficient blood for the sample can be frustrating and stressful, as blood flow from a finger prick is often inadequate to fill the collection tubes.
Even when enough blood is collected, the sample may still be unsuitable for analysis if the quality has been compromised.
For example, excessive squeezing or “milking” of the finger to encourage blood flow can affect the sample and may result in it being rejected by the lab.
For larger blood panels, a venous blood draw is a must and a much easier, more reliable and less frustrating experience.
Checking for hormones
If you’re having hormone tests and you’re still menstruating, it’s important to time your blood draw correctly.
Female hormone levels fluctuate throughout the menstrual cycle, so the ideal time to test depends on which hormones you’re measuring.
For example, progesterone is best tested during the luteal phase, when levels are naturally at their highest, while oestrogen is often best assessed during the early follicular phase, when levels begin to rise.
These hormones can still be tested at other times in the cycle, but the timing needs to be taken into account when interpreting the results to ensure they are assessed accurately.
Timing isn’t the only factor that matters; alcohol intake, sexual activity and strenuous exercise before a blood test can also affect certain hormone levels and other blood markers, so these should be taken into account when preparing for testing.
Fasting and supplements?
I always advise my clients to fast overnight before a blood draw and to stop taking any vitamin supplements for at least two weeks beforehand.
These instructions aren’t always mentioned by GPs or testing companies, but they’re important if you want the most accurate results.
Some markers, including glucose, cholesterol (lipid) markers and iron, are best assessed from a fasted blood sample.
If you’re testing vitamin levels, it’s also important not to take supplements beforehand; otherwise, your results may reflect the vitamins you’ve recently taken rather than your body’s true nutritional status.
Have you been thinking of getting a clearer picture of your health markers?
Lately, I’ve been running my comprehensive blood test with many clients, new and old.
My comprehensive blood test with 60 biomarkers of health gives you a detailed overview of key areas of your health, helping to identify potential imbalances and areas that may benefit from additional support.
It’s included in the Wellness Check and can be added to a Personalised Nutrition Programme.
By looking at a wider range of markers alongside your symptoms, lifestyle and health goals, we can build a more complete picture of what’s going on in your body and create a targeted plan to support your wellbeing.
The professional lab I use offers a convenient home blood draw service, with a trained phlebotomist coming to your home to collect your sample.
This makes the process simple, comfortable and hassle-free.
Have you ever been told “your blood tests are normal” but you still don’t feel like yourself?
Looking at your health markers is about more than just whether a number falls inside a standard reference range.
Your test results are never interpreted in isolation.
I assess them alongside your symptoms, lifestyle and personal health goals, using functional medicine optimal reference ranges rather than the broader ranges commonly used in conventional medicine.
This helps identify subtle imbalances that may be contributing to your symptoms long before they fall outside the conventional “normal” range, allowing us to provide personalised nutrition and lifestyle support.
Your body often gives you signs before things become a diagnosis — understanding those signs can help you take proactive steps towards better health and wellbeing.
So if your doctor says your test results are fine but you don’t feel like all is fine, then it’s time to make the first step towards taking control of your health.
I can support you with your health testing, making the process simple, comfortable and stress-free for you, while helping you along your journey to start feeling better.
With a professional blood draw arranged to strict standards, you can relax knowing your sample is collected correctly and the details are taken care of — without the worry of navigating it all yourself.
If you’d like to find out more, let’s have a chat.