How to Read Blood Test Results

How to read your blood test results

Most people open a blood test report, see a column of numbers, and look for whichever values the lab has flagged red. That is the wrong lens. How to read blood test results properly means three things: knowing what each marker actually measures at the cellular level, knowing the population reference range your lab uses, and knowing the narrower functional range associated with metabolic health, hypertrophy capacity and recovery. The number on the page is the input. Interpretation is the work.

To understand blood test results in this deeper sense, you also need to read the markers in clusters rather than one at a time — the interpretation of blood test results emerges from the pattern across a panel, not from any single value. Blood work results meaning changes when you move from “is this number flagged?” to “what does this constellation of values say about my insulin signalling, my thyroid output, my iron stores, my recovery state?” That is the work the decoder above does.

This page walks the panel-by-panel logic the decoder applies above. Pick the marker in the tool to see its individual interpretation; read the panel sections below to understand how the markers in that panel work together, what patterns mean what, and where the standard “in range” verdict can hide a real problem. The Blood Test Decoder above accepts your numbers and returns a structured read; the prose below is the underlying blood test interpretation framework — the lab test results and what they mean — so you can read future panels without it.

This is educational. It is not a diagnosis. Always discuss your own results with a qualified clinician before acting on them.

Reference range vs functional range — the difference that matters

A standard lab report puts your value next to a population reference range. That range is built from a sample of people who walked into a lab and got tested. It is not a range of healthy people. It is a range of people who got tested, which includes everyone managing chronic conditions, on medication, deconditioned, sleep-deprived, or otherwise sub-optimal. By construction, a value sitting comfortably inside that bracket can still be associated with insulin resistance, sub-clinical hypothyroidism, low-grade inflammation, or impaired recovery.

The functional range is narrower. It is the range associated with the metabolic and hormonal state you actually want: insulin-sensitive tissue, balanced thyroid output, lipid trafficking that does not deposit visceral fat, micronutrient status that supports muscle protein synthesis. In our work with clients, we routinely see fasting glucose at 95 mg/dL flagged as “normal” on the lab report, when cohort data show a continuous risk gradient through the conventionally-normal range — men with fasting glucose 91-99 mg/dL had substantially higher diabetes risk than men at 81-90 mg/dL in the Tirosh young-adult cohort (Tirosh et al., NEJM, 2005). Same number on the slip. Different read on what it means.

The decoder above applies functional ranges where the literature supports them, alongside the standard reference range your lab will have printed. When the two disagree, the functional range tells you where to investigate; the lab's reference range tells you whether your clinician is likely to act. Both readings matter, for different reasons. Where a "functional" cutoff is functional-medicine convention rather than guideline-supported, we say so explicitly below.

Comprehensive Metabolic Panel (CMP) — results explained

CMP blood test results explained, properly: 14 markers covering kidney function (BUN, creatinine, eGFR), electrolytes (sodium, potassium, chloride, calcium), liver function (ALT, AST, ALP, bilirubin, albumin, total protein), and glucose. The same set is also searched as metabolic panel blood test results explained — same 14 markers, same logic, different phrasing. It is the panel most clinicians order for an annual check, because it gives a metabolic snapshot in one tube of blood.

Read it as four sub-systems, not 14 isolated numbers. Glucose + electrolytes tell you whether the body is handling fuel and fluid balance. BUN, creatinine, eGFR tell you how the kidneys are clearing nitrogen waste. ALT, AST, ALP, bilirubin tell you whether liver cells are stressed or leaking enzymes. Albumin and total protein tell you about long-term protein status. A single out-of-range value is rarely diagnostic; the pattern across the panel is what carries the signal.

The functional read we apply: fasting glucose 75-85 mg/dL is the band associated with insulin sensitivity in cohort data showing a continuous risk gradient through the normal range (Tirosh 2005, NEJM); 86-99 is “in range” but trending toward dysglycemia; 100+ is pre-diabetic by ADA criteria. ALT and AST are usually flagged only if elevated, but a low-normal ALT combined with elevated GGT (run separately) is a real signal of fatty liver in lean populations — the metric many clinicians miss. eGFR below 90 with normal creatinine and BUN is worth tracking even if not flagged, because protein-heavy training loads transiently elevate creatinine and BUN.

Basic Metabolic Panel (BMP) — results explained

BMP blood test results explained: a smaller version of the CMP. 8 markers, no liver enzymes, no albumin/total protein. Glucose, calcium, sodium, potassium, chloride, CO2, BUN, creatinine. Often ordered in urgent-care settings or for shorter follow-up windows when only the kidney + electrolyte + glucose snapshot is needed. The interpretation logic is identical to the CMP for the markers it shares; the difference is what you do not get — if liver function or protein status is part of your question, the BMP will not answer it. In our practice we recommend the CMP over the BMP whenever a client is paying out-of-pocket; the marginal cost is small and the interpretive depth is significantly larger.

Complete Blood Count (CBC) — results explained

The blood count test results explained: CBC reports red cells (hemoglobin, hematocrit, RBC count, MCV, MCH, MCHC, RDW), white cells (total WBC plus the differential: neutrophils, lymphocytes, monocytes, eosinophils, basophils), and platelets (count, MPV). Three sub-systems again: oxygen carriage, immune posture, and clotting. Each sub-system tells a different story.

Hemoglobin and hematocrit map to oxygen-carrying capacity. Low values associate with iron-deficiency anaemia (especially in menstruating women and endurance-trained men), B12/folate deficiency, or chronic disease. High values can reflect dehydration at the time of the draw, sleep apnea-driven secondary erythrocytosis, or genuine polycythemia — the pattern of MCV alongside hemoglobin tells you which.

The white cell differential is where the immune posture lives. Persistently elevated neutrophils with low lymphocytes is a stress + inflammation pattern (the neutrophil-to-lymphocyte ratio is the cleaner read). Lymphocyte dominance can reflect chronic viral exposure or, when combined with morphology flags, deserves further investigation. Eosinophils above the reference upper limit point at allergy, atopic conditions, or parasitic exposure depending on the clinical picture.

RDW, MCV, and red-cell pattern recognition

RDW blood test interpretation is one of the most under-read markers on a standard CBC. Red Cell Distribution Width is a measure of how much red blood cell size varies in your sample. A high RDW means the population of red cells is heterogeneous — you have new and old, large and small, in unusual mixtures. That heterogeneity is itself a signal, independent of any single value.

Read alongside MCV (the average red cell size), RDW separates the cause of an anaemia or sub-optimal oxygen carriage. Low MCV + high RDW is the iron-deficiency pattern (microcytic anaemia in development). High MCV + high RDW is the B12 or folate deficiency pattern (macrocytic anaemia). Normal MCV + high RDW alone is the early-mixed-deficiency or chronic-disease pattern, often catching iron deficiency before hemoglobin itself drops — a real interpretive win for athletes and active clients whose hemoglobin lag-indicates the underlying deficit. We've found this pattern catches 3-4 weeks earlier than relying on hemoglobin alone in clients reporting unexplained training fatigue.

Lipid panel results explained

A standard lipid panel returns total cholesterol, LDL, HDL, triglycerides, and (depending on the lab) VLDL and the cholesterol-to-HDL ratio. The 2018 ACC/AHA guideline shifted emphasis from total cholesterol to LDL and from absolute LDL to LDL particle behaviour. Total cholesterol/HDL ratio is more predictive of cardiometabolic risk than any single value; below 3.5 is the band associated with low risk in most populations.

Marker by marker. Total cholesterol is the sum of cholesterol carried in all lipoprotein particles — on its own it tells you almost nothing because it adds protective HDL cholesterol to atherogenic LDL and VLDL cholesterol. LDL cholesterol is the cholesterol cargo carried by low-density lipoprotein particles delivering lipids from liver to peripheral tissue. The atherogenic risk lives in the particles themselves, not the cholesterol they carry — which is why ApoB and LDL-P (particle number) are the more accurate cardiovascular-risk markers when you can get them. HDL cholesterol reflects HDL particle concentration, conventionally interpreted as a proxy for reverse cholesterol transport; the NCEP ATP III metabolic-syndrome cutoffs (below 40 in men, below 50 in women) are clinical risk thresholds associated with insulin resistance and elevated cardiometabolic risk. The reverse-transport mechanism framing is more nuanced than the cutoff implies: HDL-C accounts for less than 40 percent of the variation in actual cholesterol-efflux capacity (Khera & Rader, NEJM, 2011), so HDL-C is a useful clinical marker but an imperfect proxy for HDL functional capacity. Triglycerides are the storage form of fat circulating in VLDL particles; they spike post-prandially and reflect both recent dietary fat intake and, more importantly, hepatic VLDL output driven by carbohydrate load and insulin resistance. VLDL cholesterol is calculated (typically triglycerides ÷ 5) rather than measured and behaves as a triglyceride-rich-particle proxy.

The functional reads we apply. Total chol/HDL ratio below 3.5 is the metabolic-health band, 3.5-5.0 is monitor, above 5.0 flags real cardiometabolic risk. Triglyceride/HDL ratio above 3 is the single best non-invasive marker for insulin resistance and small-dense-LDL particles — the atherogenic phenotype the basic lipid panel cannot directly measure. Triglycerides above 150 mg/dL combined with HDL below 40 (men) or 50 (women) is the metabolic-syndrome pattern regardless of where LDL sits. Fasting triglycerides above 200 reliably indicate insulin-driven VLDL overproduction.

For clients with strong family history, low HDL with high triglycerides, or sub-optimal triglyceride/HDL ratio, the basic panel is not enough. ApoB (Apolipoprotein B) counts every atherogenic particle (LDL + VLDL + IDL + Lp(a)) in one number. The National Lipid Association recommends ApoB targets of below 90 mg/dL for high-risk patients and below 80 mg/dL for very-high-risk patients (Jacobson et al., NLA recommendations, 2015); ApoB target framing is lipidology-tier rather than AHA/ACC guideline (the 2018 cholesterol guideline does not formally adopt ApoB targets). LDL-P (LDL particle number) separates “a few large fluffy LDL particles” from “many small dense ones” at the same LDL cholesterol level — the latter is far more atherogenic. Lp(a) is genetically determined and unaffected by diet or statins; the 2022 European Atherosclerosis Society consensus uses ≥50 mg/dL or ≥125 nmol/L as the elevated-risk threshold (Kronenberg et al., Atherosclerosis, 2023), and the two units cannot be cleanly interconverted — if your lab reports nmol/L, use that number against the nmol/L cutoff. The decoder above accepts these advanced markers when you have the values.

Common framing problem we see in practice: clients with LDL of 130 mg/dL panic over the “high” flag. If their HDL is 70+, triglycerides are below 80, ApoB is in range, and Lp(a) is normal, the LDL number alone tells you almost nothing — large-fluffy LDL particles in the absence of insulin resistance carry far less risk than the same LDL number with low HDL and high triglycerides. The full lipid pattern is what matters; isolated LDL is the least useful marker on the panel.

Thyroid panel results explained

A complete thyroid panel covers TSH, free T4, free T3, reverse T3, and (for autoimmune evaluation) TPO antibodies. Most standard panels run TSH alone, which is the screening tool but not the interpretive endpoint. A normal TSH with a low-normal free T3 is the sub-clinical hypothyroidism pattern many clinicians miss because the standard panel does not even measure free T3.

Marker by marker. TSH (Thyroid Stimulating Hormone) is the pituitary's request for thyroid output, released in inverse proportion to circulating thyroid hormone — high TSH means the brain is shouting at an under-performing thyroid; low TSH means thyroid hormone is plentiful (or in excess). It is a feedback signal, not a measure of thyroid output itself. Free T4 (thyroxine) is the primary hormone the thyroid releases — mostly inactive, a circulating reservoir that peripheral tissues convert to active T3 as needed. Free (not total) T4 is what matters because total T4 includes hormone bound to thyroid-binding globulin and unavailable for tissue use. Free T3 (triiodothyronine) is the active form that binds thyroid receptors in cells and drives metabolic rate, basal body temperature, mitochondrial output, and recovery capacity. T3 is what tissue actually uses; everything upstream (TSH, T4) is regulation and supply. Reverse T3 (rT3) is an inactive isomer the body produces from T4 when systemic stress, sustained substrate scarcity, or inflammation signals "conserve energy" — rT3 occupies T3 receptors without activating them, effectively turning down metabolic rate at the tissue level. TPO antibodies attack thyroid peroxidase, the enzyme that builds thyroid hormone; elevated TPO is the autoimmune signature of Hashimoto's thyroiditis, often present years before TSH itself drifts.

The functional ranges we apply, with honest framing on which are guideline-supported and which are practitioner convention. TSH 0.5-2.5 mIU/L as a target band is functional-medicine convention, not a clinical guideline: AACE/ATA 2012 explicitly retains the standard reference range of approximately 0.45-4.12 mIU/L (Garber et al., Thyroid, 2012). The cohort-association case for tighter targets is real — the HUNT 12-year follow-up found TSH within the reference range was positively associated with coronary death risk in women, with high-normal TSH carrying elevated cardiovascular risk relative to lower TSH (Asvold et al., Clin Endocrinol, 2012) — but the cohort association does not establish that pharmacological treatment between TSH 2.5 and 4.5 improves outcomes. We treat TSH 2.5-4.5 as “in range, sub-optimal worth investigating”, not “treat to target”. Free T4 in the middle of the lab's reference range, not at either extreme. Free T3 in the upper third of the lab's reference range, not the lower third — clients with free T3 in the lower third routinely report cold intolerance, slow morning recovery, hair thinning, and persistent training fatigue even when TSH is “normal”. Reverse T3 below 15 ng/dL with the rT3:T3 ratio under 20 — elevated reverse T3 is the chronic-stress, over-training, and under-fuelling pattern, where the body is converting T4 into the inactive form. The 15 ng/dL functional cutoff is practitioner convention, not AACE/ATA guidance, and rT3 reference ranges vary by assay (typical lab range 8-25 ng/dL). We see elevated rT3 in clients in sustained-deficit phases beyond 12 weeks, in over-reaching training blocks, or under chronic life stress. TPO antibody cutoffs are assay-specific and vary across laboratory platforms (commonly 9, 34, 35, 60, or 100 IU/mL depending on the immunoassay kit) (Caturegli et al., Autoimmun Rev, 2014). Use your lab's stated cutoff rather than a single universal number. Above the cutoff with TSH still in range is the “Hashimoto's-but-not-yet-clinical” pattern that warrants tracking and dietary intervention before thyroid hormone replacement becomes the only option.

Pattern read: low free T3 + elevated reverse T3 + TSH still in range is the over-training / under-eating signature in athletic clients, often misread as “normal thyroid” on a standard TSH-only screen. High TSH + low free T4 is overt primary hypothyroidism. High TSH + normal free T4 is sub-clinical hypothyroidism — manageable, but worth catching early. Low TSH + high free T3/T4 is hyperthyroidism, requiring clinical workup.

Fasting glucose, A1c, and insulin — results explained

Glucose and insulin together describe metabolic flexibility — the ability to switch between burning carbohydrate and fat as fuel, the underlying axis behind most weight-loss-resistance and stubborn-belly-fat presentations. The standard CMP returns fasting glucose alone; that single value, in isolation, is the weakest reading of metabolic state available. A1c, fasting insulin, and (in advanced panels) C-peptide give the rest of the picture.

Marker by marker. Fasting glucose is the blood-sugar level after an 8-12 hour fast — it tells you what the liver is producing under no dietary input. The ADA threshold for pre-diabetes is 100-125 mg/dL and for diabetes is 126+. HbA1c (Hemoglobin A1c) is the percentage of red blood cells with sugar permanently bound to them, integrating average blood glucose over the prior 90 days — it cannot be gamed by the morning of the test the way fasting glucose can. ADA pre-diabetes 5.7-6.4%, diabetes 6.5%+. Fasting insulin is the pancreas's instruction for tissue to take up glucose; elevated fasting insulin in the presence of normal fasting glucose is the early signature of insulin resistance — the pancreas working harder to keep glucose in range. This is the marker that moves first, often years before fasting glucose drifts. HOMA-IR quantifies insulin resistance directly from fasting values (Matthews et al., Diabetologia, 1985). The formula is unit-specific: with fasting glucose in mg/dL and fasting insulin in microIU/mL, the divisor is 405 (US units); with fasting glucose in mmol/L and fasting insulin in microIU/mL, the divisor is 22.5 (SI units). Mis-applying the formula across unit systems produces values that are roughly eighteen-fold off — if your lab reports glucose in mmol/L, use the 22.5 divisor. Below 1.0 is insulin-sensitive, 1.0-2.0 is monitor, above 2.0 flags real resistance. C-peptide is released alongside insulin in equal molar amounts and gives a cleaner read of pancreatic insulin output without the hepatic-clearance noise that affects fasting insulin.

The functional reads we apply, with honest framing on the source of each cutoff. Fasting glucose 75-85 mg/dL is the band associated with the lowest cardiometabolic risk in cohort data showing a continuous gradient through the conventionally-normal range (Tirosh et al., NEJM, 2005); 86-94 is “in range, drifting”; 95-99 is the warning zone where cohort risk has measurably risen even though the lab will not flag it; 100+ is pre-diabetic by ADA criteria. HbA1c below 5.4% is the metabolic-health band based on continuous-risk cohort data showing elevated cardiovascular and diabetes risk through the 5.5-6.0 band even before the ADA pre-diabetes threshold (Selvin et al., NEJM, 2010 ARIC analysis); 5.4-5.6% is monitor; 5.7-6.4% is pre-diabetic by ADA criteria; 6.5%+ is diabetic. Fasting insulin below 8 µIU/mL as a functional target is functional-medicine convention rather than ADA/Endocrine Society guidance; assays vary, and there is no standardised clinical reference range for fasting insulin. The conventional functional bands are 8-12 monitor and above 12 with normal fasting glucose as the early-insulin-resistance pattern most clinicians miss; we use these but flag the convention-not-guideline status. HOMA-IR below 1.0 is the target for clients targeting visceral fat loss — without insulin sensitivity, the lipolytic signal cannot fire on the alpha-2-receptor-dense fat depots (belly, flanks) regardless of how aggressive the protocol looks on paper.

Why this matters for fat loss specifically. Insulin is the master switch for fat storage vs fat release. Elevated fasting insulin keeps lipolysis suppressed throughout the day — the protocol can look right on paper while the body is biochemically locked in storage mode. Lowering fasting insulin (via timing, carbohydrate load, training stimulus) restores lipolytic capacity. The decoder above flags this pattern explicitly because it is the single most actionable read for clients whose protocol is not producing the change they expected.

Metabolic syndrome and pre-diabetes — the pattern across markers

Metabolic syndrome and pre-diabetes are not single-marker diagnoses — they are constellations of marker drift that together signal a metabolic state moving toward type 2 diabetes and cardiovascular disease. Standard labs do not flag the constellation; they flag individual markers as “in range” while the pattern is already established. This is the highest-leverage pattern read on a routine panel, and the one most commonly missed.

The five-criterion metabolic syndrome (NCEP-ATP III) requires three of five: waist circumference above 40 inches in men or 35 in women, fasting glucose 100+, triglycerides 150+, HDL below 40 in men or 50 in women, and blood pressure 130/85+. The decoder above runs this check across the markers you provide. But the functional read catches the pattern earlier — we treat any of: fasting insulin above 8 µIU/mL, triglyceride/HDL ratio above 2, HbA1c above 5.4%, fasting glucose above 90 mg/dL, or elevated GGT with low-normal ALT as warning signs. Any three of those five flags a metabolic-syndrome trajectory before the formal criteria trigger.

Pre-diabetes proper is fasting glucose 100-125, A1c 5.7-6.4%, or 2-hour OGTT 140-199 — the diagnostic thresholds. The functional pre-diabetes read fires earlier: fasting insulin above 12 µIU/mL with fasting glucose still under 100 is the “hyperinsulinemic euglycemia” phase, where the pancreas is compensating for tissue insulin resistance and keeping blood sugar normal at the cost of chronically elevated insulin. This phase can last years. It is reversible with appropriate intervention. It will progress to formal pre-diabetes and then type 2 diabetes if the underlying drivers (visceral adiposity, sleep deficit, chronic stress, sedentary behaviour, hyperpalatable carbohydrate load) are not addressed.

Why we flag this hard. Insulin resistance underlies the majority of stubborn-belly-fat presentations, weight-loss plateaus, sub-clinical hypothyroidism (the inflammation-driven low T3 syndrome), and elevated cardiovascular risk — the conditions clients most often arrive with. Reading a routine blood panel through the metabolic-syndrome lens, even when no single marker is “abnormal”, is the difference between catching the trajectory and missing it for another year.

Liver function tests explained

ALT, AST, ALP, GGT, total bilirubin, and albumin together describe liver-cell stress, biliary flow, and synthetic function. ALT is the most liver-specific enzyme; AST is also produced in muscle so it rises after heavy training. The AST/ALT ratio above 2 is the alcohol-related pattern; below 1 is generally healthy. GGT is the marker most sensitive to fatty liver and to alcohol load — a low-normal ALT with elevated GGT is a real fatty-liver flag in lean clients that the basic LFT panel, read in isolation, will miss.

Kidney function tests explained

BUN, creatinine, eGFR, and urinary albumin (when ordered) describe kidney clearance. Creatinine alone is a weak metric because muscular clients produce more of it; eGFR adjusts for age, sex, and (in older equations) race. The functional read: eGFR above 90 is normal, 60-89 is “mildly decreased” but worth tracking, below 60 sustained over 3 months is the threshold for chronic kidney disease classification. Heavy protein intake transiently elevates BUN and creatinine, which can flag sub-optimal eGFR on a CMP done after a high-protein week without that being clinically meaningful.

Iron panel — results explained

The full iron blood test results explained: ferritin, serum iron, TIBC, UIBC, and transferrin saturation. Ferritin is the storage form, the most useful single marker for iron status — but it is also an acute-phase reactant, so it rises with inflammation. A normal ferritin alongside elevated CRP or hs-CRP can hide an actual iron deficiency.

Functional read: ferritin 50-150 ng/mL for most adults is functional-medicine convention rather than a guideline-endorsed range (the standard reference range typically runs 30-300 ng/mL in men and 13-150 ng/mL in women), based on practitioner observation that values in the 30-50 band often coincide with subjective fatigue and training-recovery issues even before the lab flags. Higher is acceptable for menstruating women approaching menopause; lower is acceptable for elderly clients without inflammatory markers. Transferrin saturation under 20% is a real iron-deficiency flag even if ferritin is borderline. Saturation above 45% with elevated ferritin is the hereditary-hemochromatosis screening pattern that warrants HFE genetic testing, especially in clients of Northern European ancestry; AASLD 2011 uses TSAT >45% in women and >50% in men as the iron-overload screening cutoff.

Vitamins, micronutrients, and inflammation markers

Vitamin D (25-hydroxyvitamin D), B12, folate, B6, magnesium, zinc, selenium, CRP, hs-CRP, and homocysteine cover micronutrient sufficiency and the inflammatory-tone signal. Vitamin D below 30 ng/mL is the deficiency threshold endorsed by the Endocrine Society (Holick, NEJM, 2007). The 40-60 ng/mL "functional" target you see in functional-medicine writing is observational-cohort framing (Vitamin D Council / Grassroots Health), not Endocrine Society or IOM clinical recommendation; supplementation RCTs (VITAL, D2d) have not consistently shown benefit from raising 25(OH)D above 30 ng/mL in non-deficient adults. Aim for 30+ as the floor; 40-60 is reasonable practitioner-tier framing rather than guideline-supported. B12 below 400 pg/mL with elevated MCV or homocysteine is functional B12 insufficiency in functional-medicine practice (the standard B12 lower bound of 200 pg/mL is widely considered too low); this is practitioner convention rather than BCSH-endorsed cutoff.

Hs-CRP is the inflammation marker most predictive of cardiometabolic risk; below 1 mg/L is low-risk, 1-3 is average risk, above 3 is high-risk in cardiovascular models. Homocysteine above 10 µmol/L flags B-vitamin insufficiency (B12, folate, B6) and is independently associated with vascular and cognitive risk. Together these markers paint the inflammatory + nutritional terrain a CMP cannot reach.

Pattern recognition: what your markers mean together

Single markers rarely tell the whole story. The decoder above runs pattern recognition across the values you enter; the same logic, applied here in prose, is what makes blood test results interpretation different from a list of definitions. Five patterns we apply most often:

1. Insulin resistance pattern: fasting glucose 95+, fasting insulin 10+, triglyceride/HDL ratio above 3, ALT mildly elevated, GGT elevated. Any three of five flags the pattern even if no single marker is “abnormal”.
2. Sub-clinical hypothyroidism: TSH above 2.5 with free T3 in the lower third of the range, reverse T3 elevated, basal body temperature low. Standard panels miss this because TSH is “in range”.
3. Functional B12 deficiency: B12 in the lower third of the reference range with elevated MCV or elevated homocysteine. The standard B12 lower bound (200 pg/mL) is too low; functional issues appear below 400 pg/mL.
4. Iron-deficiency-without-anaemia: ferritin under 50 ng/mL, transferrin saturation under 20%, RDW elevated, hemoglobin still in range. Catches the deficit weeks before hemoglobin drops — especially relevant for menstruating women and endurance-trained clients.
5. Chronic-stress / over-training pattern: elevated reverse T3, low free T3, morning cortisol elevated or flattened, low-normal sex hormones, hs-CRP creeping up. The pattern shows before the client subjectively recognises burnout.

Each of these is a constellation, not a single “abnormal” flag. The decoder runs the same crosswalks you would expect a careful clinician to run, and presents the patterns alongside the individual marker reads — which is what serious blood test results interpretation looks like in practice, and what the standard one-marker-at-a-time read misses.

Medications and supplements that distort lab values

Before reading any panel, check what you took in the days before the draw. Several common medications and over-the-counter supplements interfere with assays in ways that produce falsely abnormal — or falsely normal — results. The values are real, but they reflect the interference, not your underlying biology. Knowing what to flag avoids unnecessary downstream workup and avoids missing a real abnormality that the interference is masking.

Biotin (vitamin B7). The single most under-recognised lab-interference issue. The FDA issued a Safety Communication in 2017 warning that high-dose biotin (most often from over-the-counter hair-skin-nails supplements at 5-10 mg per day, but also some multivitamins and energy formulas) interferes with streptavidin-biotin immunoassays used by many labs. The classic distortion is on thyroid panels: falsely low TSH alongside falsely high free T4 and free T3, mimicking hyperthyroidism that does not exist. Other biotin-affected assays include cardiac troponin (false-negative under acute coronary syndrome), 25-hydroxyvitamin D, parathyroid hormone, and several reproductive hormones. Practical rule: stop biotin supplements at least 3 days before any lab draw; longer (up to 1 week) for very high doses (10+ mg/day).

Statins. Lower LDL and ApoB substantially; obscure the genetic-risk picture (familial hypercholesterolaemia is much harder to catch on labs of someone already on a statin). Lp(a) and HDL are largely unaffected. If you want to know your untreated lipid pattern and your clinician agrees it is safe to do so, a 2-week wash-out before draw is the conventional approach — but never stop a statin without prescriber sign-off.

Oral contraceptives and hormone therapy. Raise thyroid-binding globulin (TBG), which raises total T4 and total T3 without changing the active free fractions. Always order free T4 and free T3 (not total) on women on OCs or HRT to read thyroid status accurately. OCs also modestly raise CRP and triglycerides, lower LDL, and can raise ferritin baseline.

Glucocorticoids (prednisone, prednisolone, dexamethasone, oral or high-dose inhaled). Raise fasting glucose, fasting insulin, and HbA1c at sustained doses. They also suppress endogenous cortisol on testing, distort lipid panels (raise total cholesterol and triglycerides), and lower lymphocyte count. A patient on chronic glucocorticoids has a different baseline than the same patient off them.

Recent acute illness or strenuous training within 24-48 hours of draw. Acute-phase reactants spike: ferritin and CRP rise, transferrin and albumin fall, white-cell count rises, creatine kinase (CK) spikes after heavy training and can persist for several days. A panel drawn during or shortly after a viral illness will look inflammatory in ways that do not reflect baseline. Re-draw 2-4 weeks after recovery if the picture is unclear.

Other common interferences worth checking: high-dose vitamin C can interfere with some glucose meter readings and certain enzyme assays; metformin at sustained dosing can lower B12 over time (not an interference, a real depletion); ACE inhibitors and ARBs raise creatinine modestly via reduced glomerular pressure (a real effect, not an interference, and not pathological); thyroid hormone replacement (levothyroxine) suppresses TSH while raising free T4 — the panel is normal in the context of treatment but reading TSH alone in a treated patient is misleading; alcohol consumed within 48 hours of draw raises GGT, MCV, and triglycerides.

The decoder does not know what you took. Tell your clinician what you took. The interpretation is only as accurate as the input.

How to read blood test results — practitioner notes

Three things we tell every client before they pull their panel into the decoder. The framing applies whether you searched for “how to understand blood test results”, “interpretation of blood test results”, or simply “blood test results explained” — the questions sit on top of the same physiology.

First, read trends, not single snapshots. One value pulled at one point in time tells you where you are; three panels over six months tell you where you are going. The slope is the signal. We've had clients with a single “normal” ferritin who, looked at over a year, were dropping 30 ng/mL per panel — the trajectory caught the deficit twelve months earlier than a lab flag would have.

Second, read the panel against your training and recovery state, not in isolation. A creatinine of 1.2 mg/dL is mildly out of range for a sedentary person and entirely expected for a heavily-muscled client who trained the day before the draw. CK (creatine kinase) follows the same rule. Context is the second input.

Third, use the decoder above to flag patterns, then use a clinician to act on them. The tool is fast, defensible, and uses functional ranges the literature supports. It is not a diagnosis. In our experience, a well-prepared client who arrives at a clinical appointment with a structured read of their panel asks better questions, gets better answers, and leaves with a clearer next step than one who arrives with a stack of unreviewed lab results. That is the highest leverage this page provides.