How to Prepare for a Blood Draw — A Cheat Sheet

This is the single most important preparation step, and the one most people skip. For the full 72 hours, no resistance training, no high-intensity cardio, no intense physical activity of any kind. Light walking is fine.

The 72-hour rule is non-negotiable, but the mechanism matters. Heavy resistance training raises creatine kinase (CK) by 10-20x baseline in some cases, and myoglobin can spike too. Even moderate cardio, like a 30-minute jog, can elevate cortisol and shift your white blood cell count for up to 24 hours. If you are on a cycle, the stakes are higher: your baseline CK is already elevated from training, and a single session can push it past 2000 U/L, which will trigger a cascade of unnecessary follow-up tests. If you absolutely must train, do it 96 hours out, not 72. The extra day costs you nothing and buys you cleaner data.

Hard training sessions produce measurable changes in your blood, and those changes stick around for 48-72 hours in strength athletes.

• A creatinine elevation makes your kidneys look stressed when they are not.
• AST and ALT elevation makes your liver look damaged when it is not.
• CK elevation can exceed 1000 U/L after heavy training.
• Don't be surprised by temporary shifts in electrolytes, cortisol, and inflammatory markers.

If your AST/ALT come back elevated and you trained within 72 hours, there's no way to tell whether it's muscle or liver. You've just wasted your test.

If you already trained within 72 hours and cannot reschedule, do not panic. Ask the lab to add a CK and myoglobin test to the same draw. If CK is elevated but AST/ALT are only mildly high, the source is likely muscle, not liver. But you still cannot trust the numbers for a clinical decision. The smart move is to repeat the panel after 72 hours of full rest. That repeat test is your real baseline. One wasted draw is annoying, but two wasted draws because you ignored the first one is a pattern. Track your training dates in your phone calendar so you never book a draw on a training day again.

You don't need to eat like a monk, but you should steer clear of anything that could skew your results. That means no alcohol, because it elevates GGT and triglycerides for days, no fatty meals, since they affect lipoproteins, and no extreme changes in carbohydrate intake.

Stick to your normal maintenance diet. This isn't the moment for a cheat meal, a carb-loading day, or a prolonged fast. You want to capture your typical metabolic state, not some extreme version of it.

A normal diet means your usual macros, not a bodybuilding prep diet. If you are cutting and eating 2000 calories, that is your normal state. But do not do a refeed or a cheat meal the night before. A high-fat meal, like a burger and fries, can elevate triglycerides by 20-30% for up to 12 hours, which will wreck your lipid panel. Similarly, a carb-loading day can spike fasting glucose the next morning. If you are on a low-carb diet, your fasting glucose may run slightly higher due to physiological insulin resistance, but that is your baseline. Do not change your diet to look better on paper. You want the numbers that reflect your actual protocol.

Supplements can throw your bloodwork off in a big way. Stop all oral supplements 24 hours before your draw:

• Fish oil lowers triglycerides, which makes them look better than they are.
• Creatine monohydrate elevates creatinine, which falsely suggests kidney stress.
• Niacin can skew lipid values and cause transient enzyme elevation.
• High doses of vitamin C can interfere with glucose measurements.
• Pre-workout stimulants affect heart rate, BP, and stress markers.

Continue your injectable supplements, B12 and AAS included, exactly as you normally would. You're testing under your normal physiological conditions, so those stay in the picture. Just cut the oral stuff.

Injectable AAS and B12 stay in your system for weeks, so stopping them 24 hours before a draw would not change your levels anyway. But oral AAS like Anavar, Winstrol, or Turinabol are different. They are oral supplements, so they fall under the 24-hour stop rule. If you are taking an oral, skip the dose the morning of the draw. That gives you a cleaner read on liver enzymes and lipids, which orals hit hard. Also, do not inject any oil-based compound the day before the draw. A recent injection can cause a transient spike in estradiol or hematocrit depending on the ester. Keep your injection schedule normal, but if you can, schedule the draw at least 48 hours after your last injection.

Get your fast going 10-12 hours before the draw. Water is allowed, and honestly, it's encouraged. Coffee, tea, juice, gum, supplements: all off the table. Nothing but water.

Why fasting matters:

• Lipids: Non-fasted triglycerides are completely unreliable. LDL calculated from non-fasted values is also inaccurate.
• Glucose: Fasting glucose tells you about your metabolic health. Post-meal glucose tells you what you ate.
• Iron: Iron absorption from food can transiently elevate serum iron levels.

Set a timer on your phone. Your last bite of food lands at 8 PM, and the draw happens at 7 AM. Simple.

The 10-12 hour fast is a window, not a cliff. If you fast for 14 hours, your triglycerides can actually rise as the body mobilizes fat stores, which gives you a falsely high reading. If you fast for only 8 hours, your glucose and lipids are still influenced by the last meal. Set your last meal 12 hours before the draw, not 10. That gives you a buffer if the lab runs late. And water is fine, but do not chug a liter right before the draw. That can dilute your hematocrit and make you look anemic. Stick to the 500 mL before bed and 500 mL on waking. If you wake up thirsty, sip an extra 100-200 mL, but do not overdo it.

Dehydration concentrates your blood, which drives up hematocrit, hemoglobin, and every protein-bound marker. If you're on AAS and already running elevated hematocrit, that extra dehydration can push you from amber into red territory on paper, even though your true value would be fine once you're properly hydrated.

Schedule your draw between 7:00 and 9:00 AM, since many markers follow circadian rhythms:

• Testosterone peaks in the early morning
• Cortisol follows a diurnal rhythm
• TSH varies significantly throughout the day

If you're tracking bloodwork across multiple draws, keep the time consistent. A 3 PM testosterone reading cannot be compared to an 8 AM one.