How Dehydration Affects Your Blood Test: eGFR, Urea, Creatinine, and Electrolytes

Something as simple as hydration can dramatically impact your blood results. When you’re dehydrated, blood concentration increases, causing a spike in Urea (BUN) and Creatinine. This elevates your BUN:Creatinine ratio, often mistakenly interpreted as kidney dysfunction.

Your eGFR (a measure of kidney filtration) is calculated from creatinine, and dehydration can make it appear artificially low. Proper hydration, on the other hand, improves filtration and supports healthy lab values.

Hydration also impacts electrolytes. Low fluid or high salt intake can elevate Sodium, while too much fluid or low salt diets may drop it. Adequate Potassium and Magnesium, found in fruits and vegetables, help regulate blood pressure and kidney function.

Takeaways:

• Dehydration raises BUN and Creatinine, and lowers eGFR.
• Stay hydrated before testing — aim for 6–8 glasses of water daily.
• Balance electrolytes by moderating salt and increasing potassium (bananas, greens).
• Avoid excessive water intake, which can dilute sodium too much.
• Protect your kidneys with hydration, balanced protein intake, and caution with NSAIDs.

Test for these Biomarkers: Urea (BUN), Creatinine, eGFR, Sodium, Potassium, Magnesium

‍