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Losing weight the smart way starts with a blood test

Blood testing for people losing weight with medication — or about to start. Assessed by a registered physician. At 700+ sample locations across the Netherlands, no referral needed.

Doctor's Assessment Included
ISO 15189 Accredited Labs
Results in a Few Business Days
GDPR Compliant

Build your own test

Choose from 103 biomarkers and only pay for what you want tested. No unnecessary markers, clear results.

Which values do you track during your treatment?

Six to eight questions. You will see which values to track during your journey, and what you can skip.

From order to report in 4 steps

01

Choose your test

Choose your baseline test or follow-up, or build a custom test.

02

Receive your lab referral

You'll receive an email from ZorgDomein with a barcode within 1 business day. Orders placed outside office hours are processed from the next business day.

03

Get tested at a lab near you

Show the barcode on your phone and bring a valid ID. Done in under 15 minutes.

04

Receive your report from the doctor

A BIG-registered physician reviews your results and writes a personal report. On your dashboard within a few business days.

Five things you get with every test

01

Every value explained, with its range beside it

Each result shows the measured number, its unit and the reference range that belongs with it — plus what the value means. That matters most when you are eating less, because some values drop before you notice anything.

Three values that drop first

Vitamin B12 145 – 569 pmol/l
Folate (Folic Acid) 10 – 42 nmol/l
Vitamin B1 (Thiamine) 66.5 – 200 nmol/l

These are the ranges as they appear in your report — next to each of your own results, so you can see whether you are still inside them.

02

Your pancreas, liver and kidneys, too

Weight-loss medication calls for more than a scale. Our tests include amylase and lipase (pancreas), liver values and kidney function — values most standard panels skip.

These sit inside the Safe Weight Loss panel, not as a separate add-on.

03

No referral needed, no waiting list

You order your test yourself. No trip to the GP first, no waiting list, and no conversation beforehand about why you want this checked alongside your medication.

Order today and get your blood drawn whenever it suits you.

04

Get tested near you

You choose where to have your blood drawn. Every collection point is on the map with its opening hours — useful when you come back every three months for a follow-up.

700+ collection points across the Netherlands.

05

Reviewed by a BIG-registered physician

Your results are reviewed by a physician registered in the Dutch BIG register. That applies to your baseline and to every follow-up after it.

The BIG register is public. You can check whether a physician is in it yourself.

See what is actually changing in your blood

Your progress Week 0 to week 12
HbA1c
Start
44mmol/mol
Now
38mmol/mol
6 points lower
Fasting glucose
Start
6.4mmol/L
Now
5.3mmol/L
1.1 lower
Lipase
Start
42U/L
Now
45U/L
Stable, safety check
Every measurement explained by a doctor

Two free checks: heart risk and blood value

Two simple checks, free and without an account. Calculate your heart risk or check a blood value from an earlier result.

How long have you been on weight-loss medication?

3 months

Around three months is when treatment clinics test as standard: your blood sugar, liver and pancreas back in view.

These tools provide general information and do not replace medical advice. View all tools

Frequently Asked Questions

Medications like semaglutide and tirzepatide (GLP-1 medication, known from Ozempic, Wegovy, and Mounjaro) change more than just your weight: your blood sugar, cholesterol, and insulin often improve, while your pancreas, liver, and nutrient levels deserve attention. Treatment clinics routinely test at the start and every 3 to 6 months. If you get your medication without that monitoring, that check is missing — that's the gap SlimmerLab fills.
Mostly for the better: HbA1c, fasting glucose, insulin, and triglycerides often drop. At the same time, you'll want to keep an eye on amylase and lipase (pancreas), your liver values if you're losing weight quickly, and ferritin, B12, and vitamin D simply because you're eating much less. That's why all of these markers are included in our tests.
Only if you're already under treatment, for diabetes, for example. If you get your weight-loss medication through an (online) clinic or on your own initiative, usually no one is keeping track of your blood values. With us, you order without a referral and have an assessed report within a few business days.
Especially then. A baseline test records your starting point: your blood sugar, cholesterol, pancreas, and liver values before your first injection. Every follow-up after that gets compared with your own starting values — the most honest measure of what the treatment is doing.
We follow the same rhythm treatment clinics use: a baseline test at the start, a follow-up at 3 months, and a comprehensive blood test at 6 months. After that, testing every six months is a good habit for as long as you're using the medication.
No. We test, and a BIG-registered physician reviews and explains your results. Decisions about starting, dosing, or stopping medication are always made with your own prescriber or doctor.
No. You order directly on our site. We arrange the lab referral for you via ZorgDomein. No appointment needed, no waiting list.
Usually within a few business days after your lab visit. You'll get a notification as soon as your report is ready on your secure dashboard.
Yes. Your dashboard stores all your previous tests. Compare six-monthly or yearly follow-ups side by side and track trends in cholesterol, metabolism, and other markers. That way, you can discuss concrete data with your GP or specialist.
At 700+ certified labs across the Netherlands. Choose a location close to home. The blood draw usually takes less than 15 minutes.
We create a lab referral via ZorgDomein. You'll receive an email with a barcode within 1 business day. Orders placed outside office hours are processed from the next business day. If we need more information, we'll contact you. You can visit the lab at any time.
Two things: a valid ID and the barcode from your ZorgDomein email (showing it on your phone is fine). The lab staff will handle the rest. No BSN (Dutch social security number)? Print the referral form via the ZorgDomein patient portal.
That depends on the location. Some labs accept walk-ins, others work by appointment. You'll see this when choosing your lab location, and we'll give you a booking link if needed.
Yes. Encrypted and stored in EU data centers. Only accessible with your login credentials. Never shared with third parties. Fully GDPR compliant.
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