Lab tests in Piedras Negras: which ones require fasting and how to prepare

Your doctor ordered some lab work and the usual questions come up: can I eat breakfast? Can I have my coffee? What about my blood pressure pill? Getting ready the right way matters: a sample taken without the right fasting can come back off and send you back to repeat the test. This guide walks you through what each test needs before you arrive.

Which lab tests require fasting?

If you're getting several tests on the same day and one of them requires fasting, come in fasting for all of them. And if your doctor ordered a test that isn't on this table, ask us first: each one has its own preparation.

About cholesterol: some medical guidelines now accept a non-fasting lipid panel in certain cases. That's your doctor's call; if nobody told you otherwise, the safest choice is to come in fasting.

What does fasting actually mean?

• No food or drinks for the time you were given, usually 8 to 12 hours, except plain water.
• Water is allowed and even helps: when you're well hydrated, the blood sample is easier to draw.
• Coffee, tea, soda, juice, milk, gum and candy break the fast, even sugar-free ones.
• The night before, eat a light dinner and skip alcohol and very greasy food, especially if cholesterol and triglycerides are being measured.
• Don't stretch the fast: if you were told 8 to 12 hours, there's no need to show up after 16.
• If you ate or drank something by mistake, tell us before the draw: sometimes it's better to do it another day.

What about my daily medications?

Don't stop any medication on your own for a lab test. Ask your doctor whether to take it before or after the sample: with some treatments, such as those for diabetes or the thyroid, timing matters. Also tell us if you take vitamins or supplements, because some, like certain hair and nail products, can throw off lab results.

How to collect a urine sample the right way

• Wash your hands well with soap and water.
• Clean the genital area; women, from front to back.
• Start urinating into the toilet, stop, then fill the cup halfway with the midstream. Finish in the toilet.
• Close the cup tightly without touching the inside of the lid.
• If you collect it at home, keep it in a bag in the refrigerator and bring it in as soon as you can.
• If you're on your period, let us know: it can affect the result, and sometimes it's better to wait a few days.

Ideally, you shouldn't have urinated in the 2 or 3 hours before. When you confirm your test, we'll tell you whether the first morning urine is the better option.

Test day: quick checklist

• If you're fasting, come early: it's easier to hold out and you'll be done sooner.
• Bring your doctor's order, if you have one.
• Wear sleeves that roll up easily.
• Pack a light snack for after the draw.
• Drink plain water, even while fasting.

No doctor's order?

That's fine. The best first step is a quick consultation: the doctor examines you and tells you which tests you really need, so you don't pay for ones that won't help. Since the lab is inside the same clinic, the visit and the test happen in one trip, and once your results are in, the doctor walks you through what they mean.

Coming from Texas

Many patients from Eagle Pass, Del Rio and South Texas come over for their routine lab work. Message us before you cross to confirm how to prepare for your test; if you're fasting, leave early. On the way back, the Medical Lane at International Bridge #1 cuts the trip back to the U.S. to about 15 to 20 minutes.

At AVA Médica, our clinical lab is inside the clinic at Av. Roman Cepeda 106, Sección 1, Ejido Piedras Negras: glucose, lipid panel, thyroid panel, CBC and urinalysis, with no appointment, every day from 8 am to midnight. If you have questions about fasting or preparation, message us on WhatsApp before you come.