In one sentence
A count and a sizing of the cells in your blood: the red cells that carry oxygen and the hemoglobin inside them, the white cells of the immune system split into their five kinds, and the platelets that clot.
Why it matters
For a well adult the count answers three questions. Whether the oxygen carriers are adequate and what they are made of: a low hemoglobin with small, pale cells (low MCV and MCH) is the pattern iron deficiency produces, and large cells (high MCV) the pattern of B12 or folate shortfall, alcohol or an underactive thyroid. What the immune cells are doing: the neutrophils and lymphocytes read together as the neutrophil-to-lymphocyte ratio and, with platelets, as the Systemic Immune-Inflammation Index, two cheap measures of the immune balance that cohorts have followed. And one quiet number that turned out to carry a signal: the red cell distribution width (RDW), which says how unequal the red cells are in size. In 15,852 US adults in NHANES III, followed for about eight years, mortality rose fivefold from the lowest to the highest fifth of RDW after accounting for age and twofold after full adjustment, each standard deviation (about 1 percentage point) was associated with 23 percent higher all-cause mortality, and the association was not specific to any one cause (Perlstein 2009). The white cell count has a floor as well as a ceiling: in the Baltimore Longitudinal Study of Aging (2,803 adults, 1958 to 2002), people with a count below 3.5 or above 6.0 ×10⁹/L had higher mortality than those between (Ruggiero 2007), which is where VT's working optimal for white cells comes from.
What moves it
Hemoglobin: iron, B12 and folate; altitude and smoking (up); endurance training, which expands plasma volume and dilutes the count; dehydration, which concentrates it; menstruation and pregnancy. White cells: any infection raises neutrophils within hours, hard exercise raises the count for a few hours, smoking and corticosteroids raise it, acute stress lowers lymphocytes. Platelets rise with inflammation and with iron deficiency. RDW rises when the marrow is short of iron, B12 or folate, during recovery from a loss of blood, and with inflammation. MCV rises with alcohol and falls with iron deficiency and with inherited hemoglobin traits.
How to measure it well
A venous sample in an EDTA tube; no fasting needed. Not within two weeks of an infection or a vaccination, and not within 48 hours of hard training, because the white cells and platelets are acute-phase and the count is not the count you want. Hydrated, because dehydration raises every concentration. Use the same laboratory each time: analyzers and their reference ranges differ.
How Vitality Tracker uses it
Each of the fourteen analytes is stored as the laboratory reported it, with the laboratory's reference range and flag, which VT shows and never overrides; the differential's percentages are kept as their own series beside the absolute counts. From one draw the count feeds PhenoAge (white cells, lymphocyte percentage, MCV, RDW), the Systemic Immune-Inflammation Index and the neutrophil-to-lymphocyte ratio (neutrophils, lymphocytes, platelets) and FIB-4 (platelets), each in its own entry, and hemoglobin with MCV is read beside ferritin for iron. Beneath a result, VT's working optimal (v0.1) is shown in smaller type for two analytes only: RDW below 13.5 percent (Perlstein 2009) and white cells 3.5 to 7.0 ×10⁹/L (Ruggiero 2007); for hemoglobin (typical laboratory reference 130 to 175 g/L in men, 115 to 155 in women) and the rest, the laboratory's own range is the only line, all marked working until the clinical advisor has reviewed them. Re-test yearly, or at six months when a supplement, a medicine or heavy training is new.
How far to trust the number
Laboratory: automated analyzers with small analytical error on every analyte. Day-to-day variation is yours, and largest in the white cells, which answer to every minor infection, so a single white cell count a little outside its usual is a question for a repeat, not an answer.
Sources
- Perlstein TS, Weuve J, Pfeffer MA, Beckman JA. Red blood cell distribution width and mortality risk in a community-based prospective cohort. Arch Intern Med 2009;169:588–94. doi:10.1001/archinternmed.2009.55
- Ruggiero C, et al. White blood cell count and mortality in the Baltimore Longitudinal Study of Aging. J Am Coll Cardiol 2007;49:1841–50. doi:10.1016/j.jacc.2007.01.076
- Vitality Tracker, Recommended baseline lab panel v0.1; Lab results data model; optimal set v0.1 (working).