Articles
Labs and biomarkers 11 min
The FDA metformin label says to stop metformin when eGFR falls below 30 and not to start it between 30 and 45. Below 45, the label asks for a benefit and risk review while the ADA and KDIGO lower the dose. Before an iodinated contrast scan, the label says to stop metformin at an eGFR of 30 to 60.
Labs and biomarkers 12 min
The WHO 2016 criteria treat hemoglobin above 16.5 g/dL in men or 16.0 g/dL in women as high enough to consider polycythemia vera. The number alone diagnoses nothing: a JAK2 test, the erythropoietin level and causes such as smoking, altitude, sleep apnea, testosterone and SGLT2 inhibitors decide what it means.
Labs and biomarkers 15 min
A FIB-4 under 1.3, or under 2.0 for people older than 65, makes advanced liver scarring unlikely under the AASLD 2023 guidance and the AGA's 2026 pathway (which applies 2.0 from age 65). It is arithmetic on age, AST, ALT and platelets, it rules out advanced fibrosis rather than all scarring, and it loses accuracy under 35 and in acute illness.
Sponsored
4.0/5 our scoreAffiliate link, we may earn a commission at no extra cost to you.
Labs and biomarkers 12 min
There is no single critical hemoglobin. WHO defines severe anemia as under 8 g/dL, hospital labs set their own phone-call limits (median 6.0 g/dL across 48 US hospital lists), and the AABB recommends considering transfusion in stable hospitalized adults under 7 g/dL, with clinicians able to choose 7.5 in cardiac surgery and 8 in orthopedic surgery or cardiovascular disease, and under 10 for patients hospitalized with a heart attack.
Labs and biomarkers 14 min
The ADA uses the same A1C cut points at every adult age and for both sexes: under 5.7 percent normal, 5.7 to 6.4 prediabetes, 6.5 or above diabetes. A1C does drift up with age even when glucose is normal, which makes a borderline result after 60 worth confirming, and age changes the treatment goal for older adults with diabetes, not the normal range.
Labs and biomarkers 8 min
Creatinine reaches urine by filtration and by active tubular secretion. Drugs that block the second route, trimethoprim and cobicistat among them, raise serum creatinine and lower estimated GFR without changing filtration. For creatine supplements the measured rise is small, and the trials behind it did not include people with kidney disease.
Labs and biomarkers 7 min
An A1C below 5.7 percent is normal, 5.7 to 6.4 is prediabetes and 6.5 or above is diabetes. The test measures glucose stuck to hemoglobin over about three months, which means anything that changes the life of a red blood cell changes the result, and several common conditions do.
Labs and biomarkers 6 min
The NIH Office of Dietary Supplements treats serum B12 below 200 or 250 pg/mL as subnormal, and names methylmalonic acid as the most sensitive marker, able to confirm deficiency when serum B12 sits anywhere between 150 and 399 pg/mL. That range is wide, it covers many results reported as normal, and it is the whole reason B12 testing confuses people.
Labs and biomarkers 7 min
WHO's 2024 guideline defines anemia at a hemoglobin below 130 g/L in men and below 120 g/L in non-pregnant women aged 15 to 65. Those cutoffs are the 5th percentile of a healthy population, which means one healthy adult in twenty sits below the line by construction, and WHO itself treats anemia as a sign of something else rather than a diagnosis.
Sponsored
4.0/5 our scoreAffiliate link, we may earn a commission at no extra cost to you.
Labs and biomarkers 13 min
KDIGO defines chronic kidney disease as kidney abnormality present for a minimum of three months, so a single low eGFR cannot make the diagnosis. The classification has two dimensions, kidney function and albuminuria, and most people are only ever shown one of them.
Labs and biomarkers 7 min
The American College of Rheumatology defines asymptomatic hyperuricemia as a serum urate of 6.8 mg/dL or above with no prior gout flare and no tophi, and conditionally recommends against starting any urate-lowering drug for it. That recommendation rests on high certainty evidence, which is rare in this guideline.
Labs and biomarkers 11 min
The American College of Gastroenterology puts the true healthy upper limit for ALT at 29 to 33 IU/L for men and 19 to 25 IU/L for women, below what many laboratories flag. The most common cause of a mildly high result is fat in the liver, and the question that actually matters is not the enzyme, it is whether the liver has scarred.
Labs and biomarkers 5 min
The standard adult TSH interval is 0.45 to 4.12 mIU/L. But the 97.5th centile rises from 3.56 in your twenties to 7.49 after 80, and 70 percent of older people flagged with a TSH above 4.5 are inside their own age group's range.
Labs and biomarkers 4 min
WHO puts iron deficiency in healthy adults below 15 µg/L, and below 70 µg/L if you have infection or inflammation, because ferritin rises when you are unwell. That is why a result inside your lab's printed range can still be deficient.
Labs and biomarkers 6 min
The National Kidney Foundation publishes an average eGFR for every age band, and it falls from 116 in your 20s to 75 after 70. The threshold that defines kidney disease does not move with it. Both facts are true, and the gap between them is an open argument in nephrology.
Labs and biomarkers 5 min
The yearly core after 35: glucose or A1C (USPSTF screens adults 35 to 70 with overweight every 3 years), a lipid panel feeding the age-40 statin discussion, and blood pressure yearly from 40 (USPSTF). Kidney (eGFR) and liver (ALT) numbers ride along on standard panels and have published healthy limits. Worth doing once, not yearly: ApoB and Lp(a). Usually not worth ordering without a reason: routine vitamin D, per the 2024 Endocrine Society guideline.
We are not sending the newsletter yet. Leave your address and you will get the first one when we turn sending on, and nothing before it. Every number sourced and dated. Free, no spam.
We'll never share your email. We never sell your data.
