In one sentence
How much albumin, the blood's main protein, is leaking through the kidney's filters into your urine, measured against the creatinine in the same sample so that a dilute morning and a concentrated one read the same.
Why it matters
The filters are capillaries, and albumin in the urine is the first sign that they are being stressed, usually by blood pressure or glucose, before the filtration rate moves at all. In the meta-analysis of general-population cohorts above, the albumin-to-creatinine ratio was associated with mortality in a straight line on the log scale with no threshold below which the association stopped: compared with a ratio of 0.6 mg/mmol, the adjusted hazard of death was 1.20 at 1.1, 1.63 at 3.4 and 2.22 at 33.9 mg/mmol, and the ratio and the filtration rate multiplied each other (Matsushita 2010). The KDIGO categories laboratories print (A1 below 3 mg/mmol, A2 from 3 to 30, A3 above 30) are the working group's (KDIGO 2024). For a well adult the test is the kidney marker that moves first and the one that matters most when blood pressure or glucose is raised, which is why it is on the recommended tier rather than reserved for people with a diagnosis.
What moves it
Blood pressure and glucose over months. For a day: hard exercise within the previous 24 hours, a fever or a urinary infection, menstruation (contamination), a high-protein meal, dehydration, and standing for long periods, each of which can raise the ratio in a sample that would otherwise be quiet.
How to measure it well
A first-morning urine sample, not after exercise, not during a urinary infection or a period. A raised result is repeated before it means anything: the guideline asks for two of three samples over three months (KDIGO 2024). Ask for mg/mmol, the New Zealand unit; VT converts mg/g by multiplying by 0.113.
How Vitality Tracker uses it
Stored as reported with the laboratory's range and flag, never overridden; typical laboratory reference below 3 mg/mmol, and VT's working optimal (v0.1) is the same figure, so no second line is drawn. The KDIGO A band is shown as the guideline's. A result outside the laboratory's range prompts the consultation suggestion in the How it works page's words, and the pre-visit report lists it beside the home blood pressure protocol. Re-test every three to six months while it is raised, otherwise yearly.
How far to trust the number
Laboratory: the assay is precise; the day-to-day variation is large, which is why the guideline asks for repeats and why one raised morning is a question, not a finding.
Sources
- Matsushita K, et al. Lancet 2010;375:2073–81. doi:10.1016/S0140-6736(10)60674-560674-5>)
- KDIGO CKD Work Group. Kidney Int 2024;105(4S):S117–314. doi:10.1016/j.kint.2023.10.018
- Vitality Tracker, Recommended baseline lab panel v0.1; Lab results data model (unit conversions).