You dropped $200 on blood work and fasted for 12 hours, but you trained 48 hours ago, had coffee this morning, and took your daily supplements. So how many of those results are actually accurate?
Most athletes focus on what the blood work says without considering how much the preparation affects the numbers. The reality is that pre-analytical variables, what you do in the 72 hours before your draw, can shift results by 10-50% for certain markers. A properly prepared draw is the difference between data you can trust and data that leads you in the wrong direction.
The magnitude of these shifts is not trivial. A single heavy leg day can push CK from a normal 150 U/L to over 1,000 U/L, and it stays elevated for up to a week in some athletes. AST and ALT follow a similar curve, often doubling after intense training. Creatinine can rise 0.3 mg/dL or more, which is enough to flip your eGFR from normal to stage 2 or 3 kidney disease on paper. Even your lipid panel is affected: a hard session within 24 hours can lower HDL by 10-15% and raise triglycerides by 20-30% due to acute inflammation and free fatty acid mobilization. If you are tracking these markers to adjust your protocol, a poorly timed draw will send you chasing a problem that does not exist.
The 72-Hour Countdown Protocol
Start with your draw appointment and work backward from there. That gives you the exact protocol. Follow each step in order and your bloodwork will reflect your true physiology, not whatever your recent behavior has been doing to the numbers.
72 Hours Before: Training Stop
This is your last training session before the draw. After this, no resistance training, no HIIT, no intense cardio until blood is drawn. Why 72 hours? CK takes 48-72 hours to normalize after heavy training, and AST and ALT need a similar window. Creatinine is still elevated at 48 hours in many athletes. If you train legs or do a high-volume session, 72 hours is the minimum, 96 hours is safer. Light walking is acceptable, but nothing that elevates heart rate above 120 BPM for more than 20 minutes.
If you accidentally train within 72 hours, do not cancel the draw. Instead, reschedule if possible. If you cannot reschedule, document the training session and the time elapsed. A single heavy session 48 hours out will still skew CK and creatinine, but the trend from your next draw will be more reliable if you note it. For athletes on AAS, the bigger risk is misinterpreting a high CK as a sign of liver damage or rhabdomyolysis. A CK above 5,000 U/L after a hard leg day is common, but if you are also taking an oral like anadrol or winstrol, a licensed medical professional unfamiliar with training-related CK spikes may understandably be alarmed. Always pair CK with GGT and bilirubin to separate muscle damage from liver stress. And if you are doing a full panel, add a CRP test to gauge systemic inflammation from training.
48 Hours Before: Maintain Routine
Keep eating your normal diet, don't change anything. The goal is to capture your usual metabolic state, not a version of you that ate differently for three days. Drink 2-3 liters of water throughout the day. Avoid alcohol completely, even one drink can affect liver enzymes and triglycerides. And stop any pre-workout supplements or stimulants you were using before training.
24 Hours Before: Rest and Hydrate
Take a complete rest day. No exercise of any kind beyond walking, and keep that light. Keep drinking 2-3 liters of water throughout the day. Skip high-fat meals in the evening, they can skew triglycerides and glucose metabolism the next morning. Stop fish oil supplements 24 hours before your draw, they can transiently elevate liver enzymes in some people. Start your fast after 8 PM, water only from that point on.
Alcohol is a bigger problem than most athletes realize. Even a single beer the night before a draw can raise GGT by 20-30% and triglycerides by 15-25% the next morning. If you drink heavily two nights before, your liver enzymes can stay elevated for 48-72 hours. The protocol says avoid alcohol completely for 72 hours, but if you slip up, be honest with yourself. A single drink 48 hours out will still affect your GGT and HDL. If you are on orals, alcohol compounds the liver stress and can make your AST and ALT look like they are climbing when they are actually just reacting to the alcohol. For a clean read, treat alcohol like a training session: stop 72 hours out, and if you cannot, push the draw back a day.
12 Hours Before: Fast Begins
From here until the draw, it's water only. No gum, no mints, no black coffee, no "just a splash of creamer." A true fast means nothing but water. Even black coffee can elevate cortisol, free fatty acids, and glucose, all of which affect multiple markers. Prioritize sleep: aim for 8 hours. Poor sleep elevates cortisol and can affect fasting glucose, TSH, and testosterone readings.
Draw Morning: Execute
Wake up, drink 500 mL of water (overhydration is better than dehydration), and head to the lab. No coffee, unless you always drink coffee before every single blood draw. Consistency matters more than perfection: if you always have coffee before your draw, having coffee gives you consistent data. But if you sometimes do and sometimes do not, skip it. No supplements, no nicotine, no food. Draw between 7-9 AM for optimal results. Afternoon draws give systematically different values for cortisol, TSH, iron, and testosterone.
The 500 mL of water on draw morning is a sweet spot. It prevents dehydration, which can falsely elevate hematocrit, hemoglobin, and total protein. But do not go overboard. Drinking 1-2 liters in the hour before your draw can dilute your blood and drop hematocrit by 2-3 points, which might make you look anemic or mask polycythemia from AAS. The goal is light yellow urine, not clear. If you are on a diuretic or have high blood pressure, stick to the 500 mL and do not add electrolytes unless you normally take them. Also, do not chew gum or use mouthwash with alcohol. Both can affect glucose and liver enzymes. Just water, and sit quietly for 10 minutes before the draw to let your heart rate and cortisol settle.
The Coffee Exception
Supplement Stop List
Several common supplements will throw off your blood markers, so you need to stop them before the draw. Here's the full stop list with the washout time required for each one.
Beyond the obvious supplements, check your pre-workout and protein powder labels for hidden ingredients. Many pre-workouts contain 1,3-DMAA or yohimbine, which can raise blood pressure and cortisol for hours. Some protein powders are fortified with creatine, even if the label does not say it on the front. And a surprising number of multivitamins contain biotin at 1,000-5,000 mcg, which is enough to interfere with thyroid and testosterone immunoassays. If you are taking any supplement that you are unsure about, stop it 72 hours out. The cost of a missed dose is nothing compared to a misleading result. For athletes on TRT, a falsely low testosterone from biotin interference could lead to an unnecessary dose increase, which is exactly what you want to avoid.
- Creatine: stop 72 hours before. Creatine directly elevates serum creatinine by 0.2-0.4 mg/dL, which can drop your eGFR into stage 3 kidney disease territory even with perfectly healthy kidneys.
- Pre-workout stimulants: stop 48 hours before. Caffeine and other stimulants affect cortisol, glucose, and blood pressure. Some also contain creatine or niacin (which causes a flush that interferes with certain assays).
- Stop fish oil 24 hours before, since high-dose fish oil can transiently elevate liver enzymes and affect platelet function markers.
- Stop TUDCA 12-24 hours before your blood draw. It directly affects bile acid metabolism and can suppress GGT readings, which gives you a falsely reassuring picture of liver health.
- Vitamin C (high dose): stop 12 hours before. High-dose vitamin C interferes with certain glucose and creatinine assays, causing false readings.
- Biotin: stop 72 hours before. Biotin interferes with immunoassay-based tests, including thyroid markers, testosterone, and certain cardiac markers. Many pre-workouts and hair/skin supplements contain biotin.
Biotin is the sneakiest one because it is in so many products. Hair, skin, and nail supplements are the obvious culprits, but biotin is also added to some B-complex vitamins, electrolyte powders, and even certain protein bars. The FDA has reported that biotin at 10 mg per day can cause false results in troponin, thyroid, and testosterone tests. Even at 300 mcg, it can affect some assays. The 72-hour washout is conservative, but if you have been taking high-dose biotin for months, it can take up to a week to clear. If you are on a protocol that includes biotin for hair loss, stop it at least 72 hours before every draw. And when you get your results, ask the lab if they used biotin-interference-resistant assays. Most modern labs do, but not all.
Supplements You Can Keep Taking
Draw Timing: Why Morning Matters
Most athletes don't realize how much the clock affects their bloodwork. Markers follow diurnal rhythms, and a draw at 2 PM instead of 8 AM can produce results that look like they came from a different person:
- Testosterone: 25-40% higher at 8 AM than at 2 PM. A morning draw gives your true peak. An afternoon draw can make you look hypogonadal.
- Cortisol: peaks at waking, declines through the day. Afternoon cortisol is naturally 50-60% lower than morning.
- TSH: peaks overnight, lowest in the afternoon. An afternoon TSH can be 30-50% lower than morning.
- Iron: highest in the morning, declining through the day. Afternoon iron can be 20-30% lower than morning.
The solution is simple: draw between 7-9 AM, fasted, every time. If your schedule forces an afternoon draw, log it and stick to that same time slot for all future draws. Consistency is what keeps your trends meaningful.
The Consistency Principle
The single most important concept in blood work preparation is consistency between draws. A perfectly optimized draw is less valuable than two consistently prepared draws, because the trend, the change from one draw to the next, tells you more than any absolute number.
If you always have black coffee before your draw and always draw at 10 AM, your trends are valid even if the absolute numbers would be slightly different under perfect conditions. What you want to avoid is variability: coffee one draw, no coffee the next; morning one draw, afternoon the next; well-hydrated one draw, dehydrated the next. That variability introduces noise that masks real trends and generates false alarms.
Get your protocol standardized, document your conditions, and repeat it every time. The trend is what you need to watch for managing your health on AAS, not the absolute number.