Most blood-test questions don't need a 1500-word article to answer. They need 60 words and a link. This page is the quick path. Each answer is a one-paragraph summary with the relevant range, what an out-of-range reading typically means, and a link to the deep BiologicalX article.
The longevity-relevant biomarker work the answers below pull from is anchored in Levine et al. 2018's PhenoAge framework ( Levine et al. 2018 ), which uses 9 routine bloodwork markers plus chronological age to compute a biological-age estimate that outpredicts chronological age for all-cause and disease-specific mortality. PhenoAge informs how the longevity-optimal bands below sit relative to the lab's "normal" range.
Inflammation and immune
What does a high CRP mean?
C-reactive protein is an acute-phase protein that rises within hours of inflammation, infection, or tissue injury. High-sensitivity CRP (hs-CRP) under 1 mg/L is low cardiovascular risk; 1-3 mg/L is intermediate; over 3 mg/L is high. Persistent hs-CRP above 2 mg/L predicts cardiovascular events independently of LDL cholesterol (Ridker JUPITER trial cohort, Ridker et al. (JUPITER) 2008, n=17802 ). Acute infection drives transient peaks ten to thousands-fold higher; recheck after recovery. Full deep-dive in /posts/crp-c-reactive-protein/.
What's a normal albumin level?
Serum albumin in healthy adults runs 3.5-5.0 g/dL on most reference ranges. The longevity-optimal band sits higher: 4.3-5.0 g/dL. Below 3.8 g/dL roughly doubles all-cause mortality in older adults (Goldwasser 1997, Goldwasser & Feldman 1997 ). Low albumin flags inflammation, malnutrition, or liver/kidney synthesis problems. It is a downstream marker rather than something to chase pharmacologically. Deep dive: /posts/albumin-blood-marker/.
What does a high WBC count mean?
White blood cell count between 4.0 and 11.0 K/uL is the standard reference range. Persistent elevation above 9-10 K/uL without acute infection flags chronic low-grade inflammation, smoking, or hematologic abnormality. Persistent under 4.0 K/uL in the absence of recent infection or chemotherapy needs workup. The longevity-optimal band on the PhenoAge construct sits at 4.5-7.0 K/uL. See /posts/wbc-white-blood-cell-count/.
Lipids and metabolism
What is ApoB and why does it beat LDL?
Apolipoprotein B is the single protein on every atherogenic lipoprotein particle (LDL, VLDL, IDL, Lp(a)). One ApoB per particle. Counting ApoB counts the actual atherogenic particle burden, which is what drives coronary plaque, rather than the cholesterol cargo (LDL-C), which can be high or low at the same particle count. Optimal ApoB for primary prevention is under 80 mg/dL; aggressive prevention pushes under 60 mg/dL. Deep dive: /posts/lipid-panel-apob-framework/.
What's a normal fasting glucose?
Fasting glucose under 100 mg/dL is normal, 100-125 mg/dL is prediabetes, 126+ is diabetes. The longevity-optimal band sits at 80-90 mg/dL; values consistently above 95 mg/dL flag insulin resistance even within "normal" range. A single elevated reading isn't diagnostic; trend across 3-6 months matters more. Deep dive: /posts/fasting-glucose-marker/.
Hematology
What does a high MCV mean?
Mean corpuscular volume measures average red blood cell size. Reference range 80-100 fL. Above 100 fL (macrocytic) flags B12 or folate deficiency, alcohol use, or hypothyroidism. Above 96 fL even within reference range predicts mortality risk in epidemiological cohorts (Solak 2014 in renal disease, Solak et al. 2014 and Yoon 2016 in general population, Yoon et al. 2015 ). Below 80 fL (microcytic) flags iron deficiency or thalassemia. Deep dive: /posts/mcv-mean-corpuscular-volume/.
What does a high RDW mean?
Red cell distribution width measures size variability of red blood cells. Reference range 11.5-14.5%. Elevation above 14.5% predicts all-cause mortality across multiple cohorts independent of hemoglobin or MCV (Patel 2010 NHANES, Patel et al. 2010 ). The signal is non-specific: chronic inflammation, iron/B12 deficiency, recent transfusion, or bone marrow stress all elevate RDW. Persistent elevation warrants workup. Deep dive: /posts/rdw-red-cell-distribution-width/.
What's a normal lymphocyte percent?
Lymphocyte percent on a CBC differential runs 20-40% in healthy adults. Below 20% (lymphopenia) in the absence of acute illness flags chronic inflammatory state, immune compromise, or steroid use. Above 40% can indicate viral infection or lymphoproliferative disorder. The percent is interpreted alongside total WBC; isolated low lymphocyte percent at normal WBC is meaningful. See /posts/lymphocyte-percent-marker/.
Liver and kidney
What does high alkaline phosphatase mean?
ALP is an enzyme present in liver, bone, kidney, and intestine. Reference 40-130 U/L for adults. Liver-pattern elevation (with elevated GGT) flags cholestasis or biliary obstruction. Bone-pattern elevation (without GGT) flags increased bone turnover (post-menopause, fractures, Paget's disease). The longevity-optimal band sits at 40-90 U/L; above 110 U/L raised all-cause mortality 1.5x in some post-MI cohorts. See /posts/alkaline-phosphatase-marker/.
What does creatinine measure?
Serum creatinine is a kidney-function marker, the breakdown product of muscle creatine. Reference 0.7-1.3 mg/dL for men, 0.6-1.1 for women. Higher in muscular individuals; lower in low-muscle-mass states. The clinically useful number is eGFR, which mathematically converts creatinine + age + sex into estimated glomerular filtration rate. Persistently elevated creatinine flags reduced kidney filtration. Deep dive: /posts/creatinine-blood-marker/.
Thyroid and hormones
What's a normal TSH?
Thyroid-stimulating hormone reference range 0.4-4.0 mIU/L. The functional optimum sits tighter: 1.0-2.5 mIU/L for most adults. Above 2.5 with symptoms (fatigue, cold intolerance, weight gain) suggests subclinical hypothyroidism worth a free-T4 follow-up. Below 0.4 with symptoms suggests subclinical hyperthyroidism. TSH alone is insufficient when symptoms are present; pair with free T4 and free T3 for a full picture.
What does total testosterone tell you?
Reference range for men is 264-916 ng/dL on most assays. The clinically useful number is free testosterone, not total, because SHBG (sex hormone-binding globulin) varies with age and metabolic state. Total testosterone under 300 ng/dL with symptoms (low libido, fatigue, depression) is the conventional hypogonadism cutoff. Cycle considerations and time-of-day matter; 7-9 am draws are standard.
What this isn't
This is not a diagnostic tool. Every answer above ends with "see your clinician" implicitly; persistent out-of-range readings warrant clinical workup, and individual context (medications, recent illness, family history) shifts interpretation. The bands are population-derived; your individual context can move them.
It is also not a complete biomarker reference. The 20+ questions above are the most-Googled subset of the BiologicalX coverage. Compounds, pillar articles, and the longevity-specific PhenoAge framing live in the deeper articles linked above.
Use this page as the entry point. The deep articles are where the actual interpretation work happens.
