Laboratory PhenoAge Explained: A Blood-Based Estimate Beside Your Index

Your Apple Watch notices how you sleep, move and recover. A blood test records something it can't: your blood chemistry and blood cells on a single morning. PhenoAge combines nine routine results from that kind of test with your age into one age-like number. Laboratory results, coming in My Bio Age 1.0.23 and now in development, can show this estimate for an eligible report beside your MyBioAge Index™.

Where PhenoAge comes from

PhenoAge, short for phenotypic age, was described by Levine and colleagues in 2018. Using data from the third US National Health and Nutrition Examination Survey (NHANES III), they narrowed 42 candidate clinical measures to nine blood markers and combined them with chronological age into an estimate expressed in years.

A follow-up study by Liu and colleagues applied the same formula to a later, separate NHANES sample of more than 11,000 adults, comparing groups by age, sex, race and ethnicity, and health. They describe the number as the age, within the study population, that matches a person's estimated mortality risk, and in the later sample it tracked mortality and the number of health conditions across these groups. That is a statistical pattern in groups of people, not a lifespan forecast for anyone. The authors noted a limit: their data did not follow how each person's value changed over time.

The 2018 paper also used the blood-based estimate to build a DNA methylation clock. My Bio Age uses only the blood-based model, so importing a report is not an epigenetic test.

The nine blood markers

All nine are routine tests. Five come from blood chemistry, described here using MedlinePlus:

Albumin. A protein made by the liver that helps keep fluid in your blood vessels and carries hormones, vitamins and enzymes.
Creatinine. A waste product made when your muscles work, which healthy kidneys filter from the blood.
Glucose. The sugar in your blood and your body's main energy source. Some glucose tests follow a fast; others can be done at any time.
C-reactive protein (CRP). A protein the liver makes in response to inflammation.
Alkaline phosphatase (ALP). An enzyme found throughout the body, with higher amounts in the liver, bile ducts and bones.

The other four come from a complete blood count (often called a full blood count) with a differential, which breaks the white cells down by type:

White blood cell count. The total number of the cells that help your body fight infection and disease.
Lymphocyte percentage. The share of white blood cells that are lymphocytes, one of five main types, reported in a blood differential. A basic count gives only the total, and the app needs the percentage rather than an absolute lymphocyte count.
Mean cell volume (MCV). The average size of your red blood cells.
Red cell distribution width (RDW). How much your red blood cells vary in size. My Bio Age uses the RDW-CV version, reported as a percentage.

PhenoAge weighs all nine together with your age, so no single marker decides the estimate.

When My Bio Age can calculate it

The published model was built from complete blood panels in adults, so the app calculates an estimate only when a report fits. It needs:

A reviewed report. You confirm the report details and check each result against the original PDF.
A confirmed collection date. Not in the future, and within the last six months. That limit is an app policy, not part of PhenoAge, so an older report stays in your history without an estimate.
Your age at collection. You enter it, and it must be 20 or over.
Pregnancy status. You confirm you were not pregnant at the time. This is also an app policy rather than part of PhenoAge.
All nine markers from the same report. Each must be a blood result written as an exact number in a supported unit.

The app won't fill gaps. A result written as “<5” is never treated as 5, and a missing marker isn't borrowed from a different blood draw. When something is missing, the report's PhenoAge section lists which markers need attention, and a report without an estimate is still kept as a record.

Why it stays separate from your Index

The MyBioAge Index™ is a weekly estimate built from Apple Health data, such as VO₂max, HRV, resting heart rate and sleep, across complete Monday-to-Sunday weeks. Laboratory PhenoAge comes from one blood draw and a published formula. The inputs, methods and timescales all differ.

So the laboratory estimate isn't blended into the weekly Index, its confidence, the score on your Apple Watch or your Pace of Aging. The app describes them as different measures and says combining them has not been validated to improve accuracy. Agreement or disagreement between the two validates neither. As we noted when Apple announced Health Age, two numbers labelled “age” can calculate different things. The Index's sources mention research inspired by PhenoAge, among other frameworks, but the Index itself uses no blood results.

Reading your result

Treat Laboratory PhenoAge as a snapshot of one blood draw, not a verdict on your health.

Remember how you felt. MedlinePlus explains that CRP rises with inflammation, such as from an infection or injury, and that your body makes more white blood cells when you are sick. A draw taken during a cold may not reflect your usual pattern.
Compare like with like. Between reports, look for similar conditions: the same laboratory, similar timing and the same preparation, such as fasting.
Talk to your clinician. Discuss any out-of-range result or concern with your clinician, ideally the one who arranged or can interpret the test, and never change a medication or treatment because of an estimate.

The estimate is not a diagnosis, a treatment guide or a lifespan prediction, and the app shows no risk score beside it.

Privacy and where to find it

Import, text recognition and storage happen on your iPhone, and My Bio Age doesn't upload the report. Laboratory reports aren't used in the fully on-device AI Coach prompts or written to Apple Health. Saved reports are excluded from device backups, so keep your originals. Our privacy policy has the details.

Once your app is on version 1.0.23 or later, open Settings in My Bio Age, then Laboratory results under Laboratory records. Each saved report has a Laboratory PhenoAge section showing the estimate or what is still needed. Once a report is eligible, a Laboratory results card on the dashboard and the MyBioAge Index™ screen also shows your latest estimate.

Putting it together

Laboratory PhenoAge adds a dated blood snapshot beside the weekly picture your watch builds. Keeping them side by side, rather than averaged, shows where each number comes from. For the import and review steps, read our first look at private laboratory records. To compare blood panels with wearable scores and epigenetic tests, see how to compare biological age apps and tests, and for the wearable side, read how Apple Health metrics become the MyBioAge Index™.

You can start with the weekly Apple Health picture now: download My Bio Age free on the App Store. The iPhone app is completely free, with no in-app purchases, subscription or account required, and your health data is processed privately on your iPhone. Laboratory results and PhenoAge are part of version 1.0.23, still in development as of October 2026; this article previews that feature.

General wellness information, not medical advice. Discuss laboratory findings, and any symptoms, with your clinician.