PhenoAge was published by Morgan Levine and colleagues in the journal Aging in 2018.[1] Out of 42 candidate lab tests, statistical modelling selected the nine below as the combination that best predicted mortality risk. Each is a window onto a different aging system — metabolism, inflammation, kidney and liver function, immune status and red-cell health.
Albumin
Albumin is the most abundant protein in your blood, made by the liver. It keeps fluid inside blood vessels and carries hormones, vitamins and drugs around the body.
What higher or lower values indicate: Within the normal range, a higher albumin is generally regarded as favourable and is associated in population studies with lower mortality. A lower albumin can reflect chronic inflammation, liver or kidney conditions, or inadequate protein intake, and low levels have been repeatedly linked to frailty and worse outcomes in older adults.[2] Because inflammation lowers albumin, it is often read alongside CRP rather than in isolation.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Cleveland Clinic
Creatinine
Creatinine is a waste product of normal muscle metabolism that healthy kidneys filter out. It is the everyday screening marker for kidney function; doctors often convert it into an estimated glomerular filtration rate (eGFR).
What higher or lower values indicate: A higher creatinine most often signals that the kidneys are clearing less efficiently, which is why the PhenoAge formula treats rising creatinine as adding to biological age. There is an important nuance: because it comes from muscle, very muscular or high-protein individuals can have a modestly higher creatinine with entirely normal kidneys, while low muscle mass can keep it low. It is best interpreted with eGFR and, if needed, cystatin C — one reason no single marker should be read alone.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Testing.com (Lab Tests Online)
Glucose (fasting)
Fasting glucose is your blood-sugar level after not eating overnight. It is a core metabolic marker and part of how prediabetes and diabetes are defined.
What higher or lower values indicate: A higher fasting glucose points toward reduced insulin sensitivity and, at defined thresholds, prediabetes (100-125 mg/dL) or diabetes (126 mg/dL or above on repeat testing).[3] Sustained higher glucose accelerates damage to blood vessels and is why the marker adds to biological age in the model. Unusually low readings can occur with certain medications or prolonged fasting. A single value can be affected by what and when you last ate, so fasting matters for accuracy; HbA1c gives a longer-term average.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Cleveland Clinic
CRP (C-reactive protein)
CRP is a protein the liver releases when there is inflammation anywhere in the body. The high-sensitivity version (hs-CRP) can detect the low-grade inflammation relevant to long-term health.
What higher or lower values indicate: A persistently low CRP is generally favourable. A higher CRP reflects more inflammation — and chronic, low-grade inflammation is one of the most consistent threads in biological aging, a phenomenon researchers call "inflammaging".[4] The major caveat is that CRP rises sharply with any acute infection, injury or hard recent workout, so a one-off high reading during a cold says little about your baseline. It is most meaningful measured when you are well, and watched as a trend.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Cleveland Clinic
Lymphocyte percentage
Lymphocytes are the white blood cells — T cells, B cells and natural killer cells — that run your adaptive immune response. This marker is the percentage of your white cells that are lymphocytes.
What higher or lower values indicate: In the PhenoAge model a higher lymphocyte share tends to be associated with a more youthful profile, while a lower share can accompany physiological stress, acute illness or the gradual immune changes of aging (immunosenescence). Both very low and very high absolute lymphocyte counts can have specific medical causes, so unusual values are worth discussing with a clinician rather than interpreting from percentage alone.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Testing.com (Lab Tests Online)
MCV (mean cell volume)
MCV is the average size of your red blood cells. It is a standard part of the complete blood count and helps classify types of anemia.
What higher or lower values indicate: A higher MCV (larger cells, "macrocytosis") can point to low vitamin B12 or folate, higher alcohol intake, thyroid changes or certain medications, and larger cell size nudges biological age up in the model. A lower MCV (smaller cells) is often seen with iron deficiency or certain inherited traits. Because both directions have distinct causes, an abnormal MCV is a prompt to check B12, folate and iron with a doctor.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Cleveland Clinic (Complete Blood Count)
RDW (red cell distribution width)
RDW describes how much your red blood cells vary in size. It is printed on almost every blood count and usually ignored — yet it carries surprising weight.
What higher or lower values indicate: A higher RDW (more variable cell size) is, across large studies, one of the single strongest routine-blood predictors of mortality and cardiovascular risk, independent of whether you are anemic.[5] It tends to rise with nutritional deficiencies (iron, B12, folate) and with underlying inflammation, and often improves as those are addressed. A value comfortably within range is reassuring; a rising trend is worth a closer look.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Cleveland Clinic
Alkaline phosphatase (ALP)
ALP is an enzyme found mainly in the liver and bones. It is part of standard liver panels and also reflects bone turnover.
What higher or lower values indicate: A higher ALP can come from the liver or bile ducts (for example bile-flow problems) or from bone (healing fractures, and normally higher levels in growing children and pregnancy). Markedly high values deserve a clinician's assessment to identify the source. A lower ALP is less common and can occasionally relate to nutritional or rare metabolic factors. Interpreting ALP usually means looking at other liver enzymes alongside it.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Cleveland Clinic
White blood cell count (WBC)
The white blood cell count is the total number of immune cells in a volume of blood — your body's first-line defence force.
What higher or lower values indicate: A higher total WBC often mirrors inflammation, active infection or smoking, and a higher baseline count within the normal range has been associated with worse long-term outcomes in population studies — which is why it adds to biological age in the model. A lower count can follow certain infections, medications or bone-marrow conditions. Like CRP, WBC jumps during any acute illness, so a single high reading while unwell reflects that illness, not your baseline.
Further reading (independent sources): MedlinePlus, U.S. National Library of Medicine · Testing.com (Lab Tests Online)
Run the two-step biological age calculator — lifestyle first, then your blood work, all computed privately in your browser.
Open the Biological Age Calculator ->
All of these markers come from a standard blood draw. If you are in Germany, Austria or Switzerland, you can also get them checked without a doctor’s visit — via an at-home 52-biomarker blood test analysed by a certified German lab (site in German).
References
- Levine ME, Lu AT, Quach A, et al. An epigenetic biomarker of aging for lifespan and healthspan. Aging (Albany NY). 2018;10(4):573-591. PubMed · doi:10.18632/aging.101414
- Cabrerizo S, Cuadras D, Gomez-Busto F, et al. Serum albumin and health in older people: Review and meta-analysis. Maturitas. 2015;81(1):17-27. PubMed · doi:10.1016/j.maturitas.2015.02.009
- American Diabetes Association. Classification and Diagnosis of Diabetes: Standards of Medical Care. Diabetes Care. PubMed
- Franceschi C, Campisi J. Chronic inflammation (inflammaging) and its potential contribution to age-associated diseases. J Gerontol A Biol Sci Med Sci. 2014;69 Suppl 1:S4-9. PubMed · doi:10.1093/gerona/glu057
- Patel KV, Ferrucci L, Ershler WB, et al. Red blood cell distribution width and the risk of death in middle-aged and older adults. Arch Intern Med. 2009;169(5):515-523. PubMed · doi:10.1001/archinternmed.2009.11
Source: PubMed (U.S. National Library of Medicine). Algorithm: Levine et al., Aging 2018.
Disclaimer: This guide is provided as-is, without any warranty, for general education only. It is a non-binding educational resource and is not a medical diagnosis and not medical advice. Laboratory reference ranges vary, and individual results must be interpreted in clinical context. Discuss your own values — and any results that differ from your lab's reference range — with a qualified doctor. The research gold standard for biological age is a laboratory epigenetic clock such as Horvath's or DunedinPACE. © Anti-Aging Daily.