The Body Detectives

Blood test results, decoded by a doctor.

Type a number from your report and see where it sits, what it usually means and what to ask your doctor next. Every tool accepts US units (such as mg/dL) and UK units (such as mmol/L).

Popular:TSHFerritinVitamin DHbA1cCholesteroleGFRB12

Written by Dr. Mustafa Sakr, MBBCh. Education, never a diagnosis.

Your lab vs the guidelinesA sample report, read like a detective
  • TSH6.2 mIU/L0.4–4.5H

    ClueMildly raised. Free T4 shows which pattern it is.

  • Ferritin22 ng/mL15–150–

    ClueNo flag, but UK and US guidance count below 30 as low iron stores.

  • Vitamin D18 ng/mL30–100L

    ClueFlagged low on this lab’s range. Guidelines call it possibly inadequate, not deficient.

  • HbA1c6.0 %below 5.7H

    CluePrediabetes range on US (ADA) cut-offs. The start of NICE’s high-risk range in the UK.

  • Total cholesterol240 mg/dLbelow 200H

    ClueHigh on its own, but treatment depends on your overall heart risk.

Sample values for illustration. Ranges differ between labs, so always use the range printed on your own report. Tap a test to check your own number.
  • 60+ guidesto blood tests, hormones and vital signs
  • 8 free tools7 checkers and a unit converter
  • US and UK unitsmg/dL and mmol/L side by side
  • Private by designcheckers run on your device and save nothing

Free tools

Check your number in seconds

Each checker shows where your result sits against US and UK guidance, explains what it usually means and gives you three questions for your doctor.

TSH checker

Normal, high or low, with your lab’s range and an optional free T4.

mIU/L · free T4 pmol/L or ng/dL

Vitamin D checker

Deficient, possibly inadequate or sufficient, on US or UK cut-offs.

ng/mL · nmol/L

HbA1c checker

Normal, prediabetes or diabetes range, with an optional fasting glucose.

% · mmol/mol

Ferritin checker

Your iron stores by sex and menopause, with optional CRP and TSAT.

ng/mL · µg/L

B12 checker

Low, gray zone or fine, and which symptoms change the next step.

pg/mL · pmol/L

Kidney checker

Your eGFR and urine ACR placed on the KDIGO kidney chart.

eGFR · ACR mg/g or mg/mmol

Blood test unit converter

A US result and a UK range, or the other way round? Convert more than 30 common tests between US and UK units.

mg/dL ⇄ mmol/L · % ⇄ mmol/mol

See all tools and how they work →

The method

Read your report like a detective

Four steps doctors use every day. You can use them too.

  1. Spot the flags

    H and L mean a result sits outside your lab’s range. No flag doesn’t always mean nothing to see, as a ferritin between 15 and 30 shows.

  2. Check the unit and range

    The same result looks very different in US and UK units: an HbA1c of 6.0% is 42 mmol/mol. Our unit converter does the maths.

  3. Read the pattern

    One number rarely tells the story. TSH is read with free T4, ferritin with CRP, and eGFR with urine ACR.

  4. Take questions to your doctor

    Every checker ends with three questions to ask. Your doctor knows your history and decides what the result means for you.

Every guide

Find your test

All our guides, grouped by body system. Tests with a checker let you type in your own number.

62 guides

No guide matches that yet. Try another name for the test, or browse the tools.

Browse by category: Blood tests · Vitamins and minerals · Hormones and metabolism · Vitals and wearables · Case files

Case files

Follow a doctor through the clues

Fictional cases that walk through real tests, one suspect at a time.

CASE FILE 02

Heart racing for no reason?

A 26-year-old with palpitations. Stress, caffeine, low iron and heart rhythm problems are ruled in or out with an ECG and blood tests.

Why trust us

Written by a doctor, checked against the guidelines

Dr. Mustafa Sakr

MBBCh · Medical doctor

I write every guide the way I would explain a result to a patient: plainly, with the numbers that matter and the questions worth asking. More about me →

Guidelines first

Cut-offs come from bodies such as NICE, the NHS, the American Diabetes Association, KDIGO, the Endocrine Society and the NIH. Where US and UK guidance differ, we show both.

Education, never a diagnosis

We explain what a result usually means and what to ask. Only your own doctor can tell you what it means for you.

Nothing to sell

No supplements, no affiliate links and no paid placements. The site is free to read and supported by ads.

Decode Your Labs: your free pocket guide

A calm, plain-English PDF on the four blood tests that matter most, how to read a range and what to ask your doctor.

  • TSH
  • Vitamin D
  • HbA1c
  • Ferritin
  • Reading a range
  • Questions to ask
Get the free guide

The Body Detectives is for education only and isn’t medical advice, a diagnosis or a substitute for your own doctor. Reference ranges vary between laboratories. If you feel very unwell, get urgent medical help. Read our medical disclaimer and privacy policy.