15/01/2026
Trained before a blood test? Here’s why that’s a problem
If you’re training consistently - first of all, respect.
But if you’ve got blood work coming up, here’s something most people (and even many trainers) don’t know - your training can completely throw off your blood test results.
Let’s break down what happens, why it matters, and what to do instead.
How resistance training can skew blood tests:
Creatine Kinase (CK): Goes way up after training - looks like muscle damage
Creatinine: Often falsely elevated - triggers kidney concerns
AST/ALT: Liver enzymes rise from muscle breakdown - may suggest liver disease
C-Reactive Protein (CRP): Inflammation marker gets elevated - mimics infection or chronic inflammation
These are all normal responses to training. But they’re not “normal” to your doctor if they don’t know you just crushed a leg day.
Cardio can also mislead:
Cortisol: Spikes for hours after long/intense sessions
Testosterone: Can drop post-cardio - makes your levels look low
White blood cells: Rise post-exercise - suggests “infection”
Glucose/Insulin: Altered if your blood sugar hasn’t stabilised yet
So how long should you rest before a blood test?
Training type Pause before testing
Heavy resistance training 48 - 72 hours
High-intensity cardio 48 hours
Light/moderate activity 24 hours
How to prep properly:
No intense training 48 hours before
Sleep 7-8 hours the night before
Drink water (but avoid food if fasting is required)
No caffeine on test morning (unless advised otherwise)
Tell your doc/lab about your lifestyle - especially if you lift heavy
Your blood test is only as good as the prep behind it.
You work hard in the gym, so don’t let a misunderstood lab result undo your efforts or scare you unnecessarily.
Stay strong and smart.