The Hidden Impact of Dehydration on Your Blood Test Results

You’ve fasted, you’ve arrived on time, but there’s one simple factor often overlooked that can dramatically skew your lab results: hydration. A quick blood draw is a snapshot of your internal health, and if your body is running low on fluids, that snapshot can be blurred, leading to potentially inaccurate readings and unnecessary concern.

In the UK, routine blood tests are common for assessing everything from general health to the monitoring of chronic conditions. However, hydration plays pivotal roles in ensuring those results are accurate. A well hydrated body provides a clearer picture of your health, while dehydration can lead to misleading results. Let’s explore how dehydration impacts blood tests and why staying hydrated might just be the best preparation for your next lab visit.

What Happens to Your Blood When You’re Dehydrated?

When you’re dehydrated, the total volume of fluid in your body including the plasma (the liquid component of your blood)—decreases. This condition, known as hemoconcentration, occurs when the solid components of your blood become more concentrated due to a reduction in plasma volume.

Imagine a busy train car: the number of passengers (blood cells) stays the same, but with less space (plasma volume), they become packed much more tightly. This elevated concentration can lead to falsely high readings on several important blood tests, which may cause unnecessary alarm.

🔬 Key Blood Tests Affected by Dehydration

Dehydration can influence several key markers in your blood, potentially mimicking serious health conditions. Here are some of the critical tests that dehydration may affect:

1. Complete Blood Count (CBC) Components:

• Red Blood Cells (RBCs) & Hemoglobin/Hematocrit: Dehydration can make these values appear falsely elevated. For instance, a high hematocrit may suggest a blood disorder, but it may simply indicate a temporary fluid deficit.

• Platelet Count: Just like RBCs, platelets become more concentrated, leading to a falsely high platelet count (thrombocytosis). This spike might be misinterpreted as a sign of an inflammatory condition or even a bone marrow issue.

2. Kidney Function Tests:

• Blood Urea Nitrogen (BUN) and Creatinine: These waste products often appear elevated when you’re dehydrated. Dehydration reduces blood flow to the kidneys, impairing their ability to clear these toxins, leading to increased levels in the bloodstream.

• Estimated Glomerular Filtration Rate (eGFR): The eGFR is a key measure of kidney function calculated using creatinine levels. If your creatinine is artificially elevated due to dehydration, the eGFR may appear abnormally low, which could suggest kidney disease. Accurate eGFR readings are critical to avoid misdiagnosis.

3. Electrolytes & Glucose:

• Electrolytes (Sodium, Potassium): Dehydration can cause electrolyte imbalances, with sodium levels often appearing elevated. The result is a skewed interpretation of your true electrolyte status, making it difficult to assess whether you have a genuine imbalance.

• Glucose: Dehydration can cause an apparent increase in blood glucose levels. This might lead to a misdiagnosis of pre-diabetes or diabetes, as dehydration can affect glucose metabolism.

4. Liver Enzymes:

• Alanine Transaminase (ALT) and Aspartate Transaminase (AST): Severe dehydration can cause temporary elevations in liver enzymes due to reduced blood flow to the liver. Although these increases are typically reversible with rehydration, persistent elevations should be evaluated further to rule out underlying liver disease.

✅Your #1 Prep Tip: Drink Water!

The good news is that the solution is simple. To ensure your blood test results are as accurate as possible, make hydration a priority. In fact, a glass of water could be your best tool in ensuring reliable results.

• Before You Go: Drink a glass or two of water an hour before your appointment. This ensures that your blood volume is optimal and your veins are easier to access.

• Fasting is for Food, Not Water: If your blood test requires fasting (for example, cholesterol or glucose testing), the rule is typically no food or drinks other than water. It's crucial not to skip water during this period, as dehydration can severely skew your results.

• The Phlebotomist Will Thank You: Well hydrated veins are easier to locate, making the blood draw quicker and less uncomfortable for both you and the technician.

Hydration in the Context of UK Healthcare

In the UK, the importance of hydration before blood tests is highlighted by several health organisations. The National Health Service (NHS) advises that staying well hydrated before a blood test can improve the experience for patients and healthcare professionals alike. Dehydration can cause a number of other issues, including fainting or feeling lightheaded during a blood draw, further complicating the testing process.

Moreover, The British Medical Journal (BMJ) notes that accurate laboratory results are critical in avoiding misdiagnosis and unnecessary follow-up tests. Inaccurate readings due to dehydration could lead to overdiagnosis of conditions like kidney disease or diabetes, which can result in additional, unnecessary treatments or investigations.

Conclusion: A Simple Step for Reliable Results

Dehydration may be a subtle factor, but its impact on your blood test results can be significant. By ensuring you are well-hydrated before a test, you’re not only improving the accuracy of your results but also helping to make the process smoother and less stressful. A simple glass of water can prevent misleading diagnoses and ensure your doctor is working with the most reliable data possible.

Always consult your healthcare provider for specific instructions regarding hydration and other pre test preparations to ensure the most accurate results possible. After all, a well hydrated body is a well prepared body.

References:

• NHS Choices, "Blood Tests: What You Need to Know" – www.nhs.uk

• British Medical Journal, "The Role of Hydration in Blood Test Accuracy" – www.bmj.com

• National Institute for Health and Care Excellence (NICE), "Hydration and Health" – www.nice.org.uk

Disclaimer: The information in this blog post is for educational and informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read in this blog. Relying on information provided in this article is solely at your own risk.