How to Interpret Blood Test Results: Complete Guide 2025

Understanding Blood Test Results

Blood test results contain crucial information about your health, but interpreting these results correctly requires understanding laboratory ranges, biological variation, patterns indicating specific conditions, and the critical distinction between "normal" and "optimal" values. This comprehensive guide provides the knowledge needed to make sense of your blood work and take appropriate action.

Modern blood testing can measure hundreds of biomarkers, from basic screening panels to advanced specialty tests. While your healthcare provider should always interpret results and recommend actions, understanding what your numbers mean empowers informed discussions, earlier recognition of concerning patterns, and motivation for health-improving interventions.

This guide covers how to read laboratory reports, interpret reference ranges, understand common blood tests, recognize patterns suggesting health issues, distinguish between normal and optimal values, and determine appropriate next steps when results are abnormal. Whether you've received results from NHS testing or private providers, these interpretation principles apply universally.

Blood Test Basics: Understanding Your Report

How to Read Laboratory Reports

Laboratory reports typically include: the test name, your result value with units (mg/dL, mmol/L, IU/mL, etc.), the reference range for that test, and often a flag indicating whether your result is low, normal, or high. Some reports include graphical representations showing where your value falls within the reference range.

Pay attention to units, as different laboratories may report the same test in different units. For example, glucose might be reported in mg/dL (common in US/UK private labs) or mmol/L (common in NHS labs). Always compare your result to the reference range provided by the specific laboratory that performed your test, not generic ranges, as reference ranges vary by testing methodology, equipment, and population.

Modern laboratory reports increasingly include interpretive comments explaining whether results are within normal limits or require follow-up. Some private testing services provide detailed interpretation reports with optimization recommendations—though these should complement, not replace, professional medical advice.

Understanding Reference Ranges

Reference ranges (also called normal ranges) typically represent values found in 95% of a reference population—specifically, values between the 2.5th and 97.5th percentiles. This statistical definition has important implications: approximately 5% of healthy individuals will fall outside the reference range for any given test simply due to normal biological variation.

Reference ranges are established by testing large numbers of presumably healthy people, measuring a specific biomarker, and defining the range that includes the middle 95%. This means "normal" reflects statistical commonality, not necessarily optimal health. In populations with high rates of metabolic disease, cardiovascular disease, or other conditions, reference ranges may include unhealthy values simply because they're statistically common.

Reference ranges vary by multiple factors: age (many markers change with aging), sex (hormones differ dramatically between males and females), ethnicity (genetic differences affect certain markers), pregnancy status, and even time of day (cortisol, testosterone, and other hormones fluctuate diurnally). Laboratories typically adjust reference ranges for age and sex, but you should verify this on your report.

Importantly, reference ranges vary between laboratories based on testing methodology, equipment calibration, and the specific population tested. This is why you should always compare your result to the reference range provided by the laboratory that performed your test. When tracking results over time, using the same laboratory improves consistency.

Biological Variation and Test Reliability

All biomarkers exhibit biological variation—normal fluctuations over time due to diet, hydration, exercise, stress, sleep, time of day, and other factors. Understanding this variation helps interpret results and avoid over-reacting to minor fluctuations.

Some markers are very stable (e.g., blood type, genetic markers), others moderately stable (e.g., HbA1c, thyroid hormones), and some highly variable (e.g., acute phase inflammatory markers, white blood cell count during infection, hormones throughout menstrual cycle). Single abnormal results for moderately or highly variable markers should typically be confirmed with repeat testing before making major clinical decisions.

Pre-analytical factors significantly affect results: fasting status (crucial for glucose, insulin, triglycerides), time of day (important for cortisol, testosterone, iron), physical activity before testing (can elevate muscle enzymes like creatine kinase), dehydration (concentrates blood components, artificially elevating many markers), and medication timing. Standardizing these factors improves result reliability and comparability over time.

Analytical variation—laboratory measurement error—also exists, though modern laboratories maintain tight quality control. Typical analytical variation is 2-5% for well-standardized tests. When tracking trends, focus on significant changes (typically >10-20% depending on the marker) rather than minor fluctuations within measurement error.

Interpreting Common Blood Panels

Complete Blood Count (CBC)

The Complete Blood Count measures blood cell types and characteristics. Understanding CBC components enables recognition of anemia, infection, immune disorders, and blood cancers.

Red Blood Cells (RBC) and Related Markers: RBC count measures the number of red blood cells per volume of blood. Low RBC indicates anemia; high may indicate dehydration, lung disease, or polycythemia. Hemoglobin measures the oxygen-carrying protein in red blood cells—optimal for men is 14-17 g/dL, for women 12.5-15.5 g/dL. Low hemoglobin defines anemia; high may indicate dehydration or polycythemia.

Hematocrit measures the percentage of blood volume occupied by red blood cells—essentially how "thick" your blood is. Optimal hematocrit for men is 42-50%, for women 37-45%. Low hematocrit indicates anemia or blood loss; high suggests dehydration or excessive red blood cell production.

MCV (Mean Corpuscular Volume) measures average red blood cell size. Low MCV (<80 fL) indicates microcytic anemia, typically from iron deficiency or thalassemia. High MCV (>100 fL) indicates macrocytic anemia, typically from B12 or folate deficiency, alcohol use, or certain medications. Normal MCV with anemia suggests acute blood loss, chronic disease anemia, or hemolysis.

MCH (Mean Corpuscular Hemoglobin) and MCHC (Mean Corpuscular Hemoglobin Concentration) provide additional information about hemoglobin content and concentration within red blood cells. These help classify anemia types and identify specific deficiencies.

White Blood Cells (WBC) and Differential: WBC count measures immune cells fighting infection and inflammation. Optimal count is 4.5-7.0 × 10⁹/L (lower half of typical reference range). Elevated WBC (>10 × 10⁹/L) suggests infection, inflammation, stress, or rarely blood cancers. Very low WBC (<3.5 × 10⁹/L) may indicate immune suppression, bone marrow problems, or autoimmune disease.

The WBC differential shows percentages of different white blood cell types: Neutrophils (50-70%) fight bacterial infections—elevated with bacterial infection or inflammation, low with viral infections or bone marrow suppression. Lymphocytes (20-40%) fight viral infections and include B and T cells—elevated with viral infections, low with immune suppression or chronic stress. Monocytes (2-10%) become macrophages that engulf pathogens—elevated with chronic infections or inflammation. Eosinophils (1-4%) respond to parasites and allergies—elevated with allergic conditions or parasitic infections. Basophils (<1-2%) release histamine—elevated with allergies or myeloproliferative disorders.

The neutrophil-to-lymphocyte ratio (NLR) serves as an inflammation marker: optimal is <2.0, elevated NLR (>3.0) indicates inflammation and increased cardiovascular mortality risk.

Platelets: Platelets enable blood clotting. Optimal count is 150-350 × 10⁹/L. Low platelets (<150 × 10⁹/L, thrombocytopenia) increase bleeding risk—causes include autoimmune destruction, bone marrow disorders, medications, or B12/folate deficiency. High platelets (>450 × 10⁹/L, thrombocytosis) may increase clotting risk—causes include iron deficiency, inflammation, or myeloproliferative disorders. MPV (mean platelet volume) measures platelet size—high MPV with low count suggests increased platelet turnover.

Comprehensive Metabolic Panel (CMP)

The Comprehensive Metabolic Panel assesses kidney function, liver function, electrolytes, and glucose—providing crucial information about metabolic health and organ function.

Kidney Function Markers: Creatinine measures waste from muscle metabolism cleared by kidneys. Optimal creatinine is <1.0 mg/dL (88 μmol/L) for men, <0.9 mg/dL (80 μmol/L) for women. Elevated creatinine indicates reduced kidney function; very low may indicate low muscle mass. BUN (blood urea nitrogen) measures urea, another kidney-cleared waste product. Optimal BUN is 10-20 mg/dL (3.6-7.1 mmol/L). Elevated BUN with elevated creatinine suggests kidney dysfunction; elevated BUN with normal creatinine may indicate dehydration or high protein intake.

eGFR (estimated Glomerular Filtration Rate) is calculated from creatinine, age, sex, and sometimes race—it estimates kidney filtering capacity. Optimal eGFR is >90 mL/min/1.73m². Values 60-89 indicate mild decrease (common with aging but still warrants monitoring), 45-59 mild-moderate decrease (stage 3a chronic kidney disease), 30-44 moderate-severe decrease (stage 3b CKD), 15-29 severe decrease (stage 4 CKD), <15 kidney failure requiring dialysis or transplant. Even mild eGFR reductions increase cardiovascular risk.

BUN-to-Creatinine ratio helps distinguish kidney dysfunction from dehydration: ratio >20 suggests dehydration or high protein intake; ratio <10 may indicate liver disease or low protein intake; ratio 10-20 is typical.

Liver Function Markers: ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes that leak from damaged liver cells. Optimal ALT is <25 U/L for men, <19 U/L for women; optimal AST is <30 U/L. Elevated transaminases suggest liver inflammation from fatty liver disease (most common), viral hepatitis, alcohol, medications, or autoimmune disease. The AST/ALT ratio provides clues: ratio <1 suggests fatty liver disease; ratio >2 suggests alcoholic liver disease or cirrhosis.

ALP (alkaline phosphatase) elevates with bile duct obstruction or bone disease. Optimal ALP is <100 U/L. Isolated ALP elevation suggests cholestasis (bile duct problems) if GGT is also elevated, or bone disease (Paget's disease, bone metastases) if GGT is normal. Bilirubin measures liver processing of hemoglobin breakdown. Optimal total bilirubin is 0.3-1.2 mg/dL (5-20 μmol/L). Elevated bilirubin causes jaundice (yellowing of skin/eyes)—direct bilirubin elevation suggests liver disease or bile duct obstruction; indirect bilirubin elevation suggests hemolysis (red blood cell breakdown) or Gilbert's syndrome (benign genetic variation).

Albumin and total protein measure liver synthetic function. Optimal albumin is 4.0-5.0 g/dL (40-50 g/L). Low albumin indicates chronic liver disease, malnutrition, kidney disease (nephrotic syndrome), or chronic inflammation. High total protein with normal albumin may indicate dehydration or chronic inflammation.

Electrolytes: Sodium, potassium, chloride, and bicarbonate maintain fluid balance and cellular function. Optimal sodium is 138-142 mmol/L. Low sodium (hyponatremia) causes confusion, seizures—common causes include excess water intake, diuretic medications, heart failure, or SIADH. High sodium (hypernatremia) causes dehydration symptoms—results from inadequate water intake or diabetes insipidus.

Optimal potassium is 4.0-5.0 mmol/L. Low potassium (hypokalemia) causes muscle weakness, arrhythmias—common causes include diuretics, diarrhea, vomiting, or inadequate dietary intake. High potassium (hyperkalemia) causes dangerous cardiac arrhythmias—causes include kidney disease, ACE inhibitors/ARBs, potassium supplements, or hemolyzed blood sample (false elevation).

Bicarbonate (CO₂ or HCO₃⁻) reflects acid-base balance. Optimal is 23-28 mmol/L. Low bicarbonate indicates metabolic acidosis (from kidney disease, diabetic ketoacidosis, or lactic acidosis); high indicates metabolic alkalosis (from vomiting, diuretic use, or respiratory disease).

Glucose: Fasting glucose measures blood sugar after 8-12 hours without food. Optimal fasting glucose is 75-85 mg/dL (4.2-4.7 mmol/L). Standard ranges define normal as 70-100 mg/dL, prediabetes as 100-125 mg/dL, and diabetes as ≥126 mg/dL on two separate occasions. However, values consistently above 90 mg/dL increase diabetes risk and warrant intervention. Random (non-fasting) glucose >200 mg/dL with symptoms suggests diabetes.

Lipid Panel Interpretation

Lipid panels measure cholesterol and triglycerides—crucial for cardiovascular risk assessment, though interpretation requires nuance as standard panels provide incomplete information.

Total Cholesterol measures all cholesterol types combined. Optimal total cholesterol is 150-200 mg/dL (3.9-5.2 mmol/L). Very low total cholesterol (<150 mg/dL) may indicate malnutrition or rare genetic conditions; very high (>240 mg/dL) increases cardiovascular risk—though total cholesterol alone provides limited information since it includes both harmful (LDL) and protective (HDL) cholesterol.

LDL Cholesterol (LDL-C) measures "bad" cholesterol in low-density lipoproteins that transport cholesterol to tissues and can contribute to arterial plaque. Optimal LDL-C for primary prevention is <100 mg/dL (2.6 mmol/L), with ideal being 70-90 mg/dL. For those with existing cardiovascular disease, target <70 mg/dL. However, LDL-C is an imperfect marker—it measures cholesterol content, not particle number. Advanced markers like ApoB or LDL particle number (LDL-P) provide superior risk assessment.

HDL Cholesterol (HDL-C) measures "good" cholesterol in high-density lipoproteins that transport cholesterol away from tissues to the liver for elimination. Optimal HDL-C is >60 mg/dL (1.55 mmol/L) for women, >50 mg/dL (1.3 mmol/L) for men. High HDL is protective against cardiovascular disease. Low HDL significantly increases risk and often accompanies insulin resistance.

Triglycerides measure fat in the blood. Optimal fasting triglycerides are <100 mg/dL (1.13 mmol/L), with ideal being 50-80 mg/dL. Standard ranges define normal as <150 mg/dL, borderline high as 150-199 mg/dL, high as 200-499 mg/dL, and very high as ≥500 mg/dL. However, triglycerides above 100 mg/dL indicate insulin resistance and metabolic dysfunction. High triglycerides result primarily from excess carbohydrate and alcohol intake.

Calculated Ratios: Total Cholesterol/HDL ratio: optimal is <3.5, higher ratios increase cardiovascular risk. Triglyceride/HDL ratio (using mg/dL units): optimal is <2, with ideal being <1. This ratio correlates strongly with insulin resistance—ratios >3 indicate significant metabolic dysfunction even if individual lipid components are within normal ranges.

Non-HDL Cholesterol (Total Cholesterol minus HDL) measures all atherogenic cholesterol. Optimal non-HDL is <130 mg/dL for primary prevention, <100 mg/dL for high-risk individuals. Non-HDL better predicts cardiovascular risk than LDL-C alone because it includes VLDL and other atherogenic particles.

Interpreting Hormone Tests

Thyroid Function Tests

Thyroid hormones regulate metabolism, energy, temperature, heart rate, cognitive function, and virtually every physiological process. Proper thyroid function testing and interpretation are essential for identifying dysfunction early.

TSH (Thyroid Stimulating Hormone): Produced by the pituitary gland, TSH stimulates thyroid hormone production. TSH is typically the first thyroid test ordered. Standard reference range is 0.4-4.0 mIU/L, but optimal for most people is 1.0-2.0 mIU/L. TSH >2.5 mIU/L may indicate subclinical hypothyroidism, particularly if symptoms are present (fatigue, weight gain, cold intolerance, constipation, brain fog, depression, dry skin, hair loss).

TSH <0.4 mIU/L indicates hyperthyroidism (overactive thyroid) or excessive thyroid hormone replacement. TSH >4.0 mIU/L indicates hypothyroidism, requiring further testing and typically treatment. TSH interpretation requires Free T4 and often Free T3 for complete assessment.

Free T4 (Thyroxine): The storage form of thyroid hormone, converted to active T3 in tissues. Optimal Free T4 is in the middle to upper half of the reference range (typically 1.1-1.5 ng/dL or 14-19 pmol/L). High TSH with low Free T4 confirms primary hypothyroidism (thyroid gland failure). High TSH with normal Free T4 is subclinical hypothyroidism—may progress to overt hypothyroidism and often causes symptoms despite "normal" T4. Low TSH with high Free T4 confirms hyperthyroidism (Graves' disease, toxic nodules, or excessive thyroid medication).

Free T3 (Triiodothyronine): The active thyroid hormone. Optimal Free T3 is in the middle to upper third of the reference range (typically 3.2-4.2 pg/mL or 4.9-6.5 pmol/L). Some people with normal TSH and Free T4 have low Free T3 due to impaired conversion—causes include selenium deficiency, chronic inflammation, liver disease, chronic stress, and certain medications. Low Free T3 can cause hypothyroid symptoms despite normal TSH and T4.

Thyroid Antibodies: TPO (thyroid peroxidase) and TG (thyroglobulin) antibodies indicate autoimmune thyroid disease (Hashimoto's thyroiditis or Graves' disease). Positive antibodies increase risk of thyroid dysfunction progression. Test antibodies if TSH is abnormal, you have a family history of thyroid disease, or symptoms suggest thyroid problems despite normal TSH.

Reverse T3 (rT3): An inactive form of T3. High rT3 relative to Free T3 (rT3/Free T3 ratio >0.2 when both are in pg/mL) may indicate cellular hypothyroidism despite normal TSH and Free T4—occurs with chronic stress, illness, inflammation, calorie restriction, or liver disease. Controversial whether isolated rT3 elevation requires treatment.

Sex Hormone Interpretation

Testosterone: Critical for muscle mass, bone density, libido, cognitive function, energy, and mood in both men and women. For men, optimal total testosterone is 550-900 ng/dL (19-31 nmol/L), with free testosterone 10-25 ng/dL (350-870 pmol/L). Values below 300 ng/dL total testosterone definitively indicate hypogonadism requiring treatment. Values 300-450 ng/dL are "low-normal" and may cause symptoms in many men, particularly if free testosterone is low.

For women, optimal total testosterone is 30-70 ng/dL (1.0-2.4 nmol/L). Low testosterone in women causes fatigue, reduced libido, difficulty building muscle, and mood changes. High testosterone in women may indicate PCOS (polycystic ovary syndrome), particularly with irregular periods, acne, and hirsutism.

SHBG (sex hormone-binding globulin) binds testosterone, making it unavailable. Free testosterone (testosterone not bound to SHBG) is the active form. High SHBG reduces free testosterone despite normal total testosterone—common with hyperthyroidism, aging in men, and high estrogen. Low SHBG increases free testosterone—common with insulin resistance and hypothyroidism.

Estradiol: The primary estrogen. For women, optimal levels vary by menstrual cycle phase and menopause status. Premenopausal women: follicular phase (days 1-14) optimal is 30-200 pg/mL, ovulation surge reaches 150-400 pg/mL, luteal phase (days 15-28) optimal is 75-200 pg/mL. Postmenopausal women typically have estradiol <30 pg/mL. Very low estradiol in premenopausal women indicates ovarian dysfunction or premature menopause. High estradiol may indicate estrogen dominance, particularly if progesterone is low.

For men, optimal estradiol is 20-40 pg/mL (70-145 pmol/L). Low estradiol in men causes joint pain, reduced bone density, low libido. High estradiol causes gynecomastia (breast tissue development), reduced libido, erectile dysfunction—common with obesity (fat tissue converts testosterone to estrogen) or aromatase excess.

Progesterone: For women, progesterone should be tested in the luteal phase (day 19-21 of 28-day cycle). Optimal luteal progesterone is >10 ng/mL (>32 nmol/L), with ideal being 15-25 ng/mL. Low luteal progesterone indicates inadequate ovulation or corpus luteum dysfunction—causes include anovulatory cycles, PCOS, stress, or perimenopause.

Cortisol and DHEA-S

Cortisol: The primary stress hormone, following a diurnal rhythm—highest in the morning, lowest at night. Morning cortisol (tested at 8am) should be 10-20 μg/dL (275-550 nmol/L). Low morning cortisol (<5 μg/dL) may indicate adrenal insufficiency (Addison's disease) or HPA axis suppression from chronic stress or steroid medications—requires urgent evaluation. High morning cortisol (>25 μg/dL) may indicate Cushing's syndrome, chronic stress, or depression.

For complete cortisol assessment, some tests measure cortisol at multiple time points (morning, afternoon, evening, night) via blood, saliva, or urine. Disrupted cortisol rhythm—flattened pattern or reversed pattern—indicates HPA axis dysfunction common with chronic stress, though treatment remains controversial.

DHEA-S: An adrenal hormone declining with age. Optimal DHEA-S varies by age and sex. For adults 40-60: men optimal 280-500 μg/dL, women optimal 140-270 μg/dL. Low DHEA-S for age indicates reduced adrenal reserve and associates with increased mortality risk, frailty, and cognitive decline.

Interpreting Specialized Biomarkers

HbA1c and Insulin

HbA1c (Glycated Hemoglobin): Reflects average blood glucose over the preceding 2-3 months. Standard interpretation: <5.7% (39 mmol/mol) is normal, 5.7-6.4% (39-46 mmol/mol) is prediabetes, ≥6.5% (48 mmol/mol) is diabetes. However, optimal HbA1c for longevity is ≤5.4% (36 mmol/mol), with ideal being 4.8-5.2% (29-33 mmol/mol). HbA1c between 5.5-5.9% significantly increases cardiovascular disease risk despite being technically "normal" and warrants aggressive lifestyle intervention.

Fasting Insulin: One of the most important yet under-tested markers. Measures insulin levels after 8-12 hour fast. Optimal fasting insulin is ≤5 μIU/mL, with ideal being 2-5 μIU/mL. Standard reference ranges extend to 20-25 μIU/mL, but values >8-10 μIU/mL indicate insulin resistance—the earliest detectable sign of metabolic dysfunction, appearing years before glucose or HbA1c rise. Fasting insulin >15 μIU/mL indicates significant insulin resistance requiring intervention. High fasting insulin with normal glucose is hyperinsulinemia—compensatory insulin secretion maintaining normal glucose at the cost of elevated insulin, which drives inflammation, weight gain, cardiovascular disease, and diabetes progression.

Inflammation Markers

hs-CRP (High-Sensitivity C-Reactive Protein): Measures systemic inflammation. Optimal hs-CRP for longevity is <1.0 mg/L, with ideal being <0.5 mg/L. Standard cardiovascular risk stratification: <1 mg/L = low risk, 1-3 mg/L = moderate risk, >3 mg/L = high risk. However, hs-CRP >1 mg/L indicates chronic inflammation warranting investigation into sources (obesity, poor diet, insulin resistance, infection, autoimmune disease, stress). hs-CRP >10 mg/L suggests acute infection or inflammation rather than chronic low-grade inflammation. Track trends—consistently elevated hs-CRP predicts cardiovascular events and mortality independent of cholesterol and other traditional risk factors.

Homocysteine: An amino acid indicating methylation function and vascular health. Optimal homocysteine is <8 μmol/L, with ideal being 5-7 μmol/L. Standard reference ranges extend to 15 μmol/L, but values >10 μmol/L increase cardiovascular disease and stroke risk. Elevated homocysteine typically indicates B-vitamin deficiency (B12, folate, B6) or MTHFR genetic variants—responds well to methylated B-vitamin supplementation.

Ferritin: Measures iron stores but also acts as an acute phase reactant (increases with inflammation). Optimal ferritin for men is 50-150 ng/mL, for women 30-100 ng/mL. Low ferritin indicates iron deficiency—causes fatigue, cognitive impairment, hair loss, and eventually anemia. Ferritin <30 ng/mL requires iron supplementation even if hemoglobin is normal (iron deficiency precedes anemia). Very high ferritin (>300 ng/mL) may indicate hemochromatosis (iron overload, requiring testing of transferrin saturation and genetic testing) or chronic inflammation (check hs-CRP).

Vitamin Status

Vitamin D [25(OH)D]: Optimal for longevity is 100-150 nmol/L (40-60 ng/mL). NHS considers >50 nmol/L (20 ng/mL) sufficient, but research shows levels >75 nmol/L (30 ng/mL) significantly reduce infection risk, autoimmune disease, cardiovascular disease, and mortality. Levels <50 nmol/L are deficient and require supplementation. Very high levels >200 nmol/L (80 ng/mL) may increase toxicity risk, though this is rare. Most UK residents require 2000-4000 IU (50-100 mcg) daily supplementation to achieve optimal levels.

Vitamin B12: Optimal serum B12 is >400 pmol/L (>550 pg/mL), with ideal being 500-900 pmol/L (680-1220 pg/mL). Values <300 pmol/L indicate deficiency despite standard reference ranges extending to 150-200 pmol/L. For accurate functional assessment, test methylmalonic acid (MMA)—elevated MMA (>270 nmol/L) indicates functional B12 deficiency even with normal serum B12. B12 deficiency causes fatigue, cognitive impairment, peripheral neuropathy, depression, and macrocytic anemia.

Folate: Optimal serum folate is >20 nmol/L (>9 ng/mL), with ideal being 25-50 nmol/L. RBC folate provides better assessment of long-term status: optimal RBC folate is >900 nmol/L. Low folate causes macrocytic anemia, elevated homocysteine, and during pregnancy increases neural tube defect risk.

Recognizing Patterns and Next Steps

Metabolic Syndrome Pattern

Metabolic syndrome is diagnosed when three or more of the following are present: waist circumference >102 cm (40 inches) for men or >88 cm (35 inches) for women, triglycerides ≥150 mg/dL, HDL <40 mg/dL for men or <50 mg/dL for women, blood pressure ≥130/85 mmHg, and fasting glucose ≥100 mg/dL. However, earlier patterns suggest metabolic dysfunction before meeting formal criteria:

Elevated fasting insulin (>8 μIU/mL) with normal glucose, triglycerides rising into upper-normal range (>100 mg/dL), HDL declining toward lower limits, triglyceride/HDL ratio >2, HbA1c creeping upward (>5.3%), elevated hs-CRP (>1 mg/L), elevated uric acid (>6 mg/dL for men, >5 mg/dL for women), elevated liver enzymes particularly GGT (>25 U/L), low-normal or declining testosterone in men, and elevated SHBG in women with PCOS.

This pattern indicates insulin resistance requiring intervention: carbohydrate restriction (particularly refined carbs and sugars), weight loss if overweight, regular exercise especially resistance training, adequate sleep, and stress management. Metformin may be appropriate if lifestyle interventions are insufficient.

Cardiovascular Risk Pattern

Beyond traditional lipid panels, comprehensive cardiovascular risk assessment includes: elevated ApoB (>90 mg/dL) or LDL particle number, elevated Lp(a) (>50 mg/dL), low HDL (<50 mg/dL), high triglycerides (>100 mg/dL), elevated hs-CRP (>1 mg/L), elevated homocysteine (>10 μmol/L), elevated fasting insulin, elevated HbA1c, declining kidney function (eGFR <90), and elevated uric acid.

Multiple abnormalities in these markers significantly increase cardiovascular event risk, warranting aggressive intervention: lipid management (statins if needed to achieve ApoB <90 mg/dL, preferably <80 mg/dL), blood pressure optimization (<120/80 mmHg), glycemic control (HbA1c <5.4%), inflammation reduction, lifestyle optimization (Mediterranean diet, regular exercise, weight management, smoking cessation), and possibly aspirin therapy if appropriate.

Thyroid Dysfunction Pattern

Overt hypothyroidism: high TSH (>4.0 mIU/L) with low Free T4, causes fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, depression, cognitive slowing—requires levothyroxine treatment. Subclinical hypothyroidism: high TSH (typically 2.5-10 mIU/L) with normal Free T4, may cause symptoms and often progresses to overt hypothyroidism—treatment is controversial but often beneficial, particularly with TSH >5.0 or positive thyroid antibodies.

Poor T4-to-T3 conversion: normal TSH and Free T4 but low Free T3—causes hypothyroid symptoms despite "normal" thyroid tests. Causes include selenium deficiency, chronic inflammation, stress, liver disease—address underlying causes; some people benefit from T3 supplementation or combination T4/T3 therapy.

Hyperthyroidism: low TSH (<0.4 mIU/L) with elevated Free T4 and/or Free T3—causes anxiety, palpitations, tremor, weight loss, heat intolerance, insomnia—requires endocrinology referral for treatment with antithyroid drugs, radioactive iodine, or surgery.

Anemia Patterns

Iron deficiency anemia: low hemoglobin, low MCV (<80 fL, microcytic), low ferritin (<30 ng/mL), high TIBC, low transferrin saturation (<20%)—requires iron supplementation (ferrous sulfate 325 mg daily or better-tolerated forms like ferrous bisglycinate 25-50 mg daily) and investigation of cause (menstrual blood loss, gastrointestinal bleeding, inadequate dietary intake).

B12/Folate deficiency anemia: low hemoglobin, high MCV (>100 fL, macrocytic), low B12 (<300 pmol/L) or low folate—requires B12 (500-1000 mcg daily sublingual or monthly injections if absorption is impaired) or folate supplementation (400-800 mcg methylfolate daily) and investigation of cause (pernicious anemia, malabsorption, inadequate dietary intake, medications).

Anemia of chronic disease: low hemoglobin, normal MCV (normocytic), normal or elevated ferritin, low iron, low TIBC—occurs with chronic inflammation, chronic infections, or malignancy. Treat underlying condition; iron supplementation ineffective and potentially harmful.

Taking Action on Your Results

When Results Require Urgent Action

Certain abnormal results require immediate medical attention: critically low or high potassium (<3.0 or >6.0 mmol/L)—causes cardiac arrhythmias, requires emergency evaluation. Severe anemia (hemoglobin <7 g/dL)—may require transfusion. Very high glucose (>300 mg/dL with symptoms)—may indicate diabetic ketoacidosis. Severe kidney dysfunction (creatinine >3 mg/dL or acute doubling)—requires urgent nephrology referral. Severe liver enzyme elevations (ALT/AST >500 U/L)—may indicate acute hepatitis or drug-induced liver injury. Extremely high calcium (>12 mg/dL)—causes serious symptoms. Very low platelets (<50 × 10⁹/L)—increases bleeding risk.

Your laboratory or testing service should contact you urgently if critical values are found. Never ignore calls or messages from laboratories regarding your results. If you receive critical results, contact your GP immediately or attend A&E if symptomatic.

When and What to Retest

Slightly abnormal results without clear clinical significance: retest in 3-6 months to confirm abnormality and identify trends. Single abnormal result that doesn't fit clinical picture: retest immediately to rule out laboratory error or pre-analytical issues. Significantly abnormal results prompting treatment decisions: retest promptly to confirm before starting medications. Monitoring treatment effects: retest 6-12 weeks after starting supplements for deficiencies, 3-6 months after lifestyle interventions, 6-12 weeks after medication changes.

Track trends over time using the same laboratory when possible—this improves consistency and enables better trend identification. Document results in a personal health record, including dates, values, reference ranges, and any interventions implemented. Longitudinal data becomes increasingly valuable for personalized health optimization.

Working with Healthcare Providers

Bring complete previous results when discussing new findings with providers—trends matter more than single values. Prepare questions in advance: What do these results mean? What could be causing abnormalities? What interventions do you recommend? What is the urgency? When should I retest? Request copies of all results for your personal records.

If results suggest optimization opportunities (e.g., suboptimal but not abnormal values), consider consulting practitioners focused on preventive medicine, functional medicine, or longevity medicine who specialize in optimization rather than just disease management. Many private testing services include doctor review and consultation in their service.

Remember that you are an active participant in your health. Understanding your blood test results empowers informed discussions with providers, early recognition of concerning trends, and motivation for health-improving interventions. Use this knowledge to advocate for comprehensive testing, appropriate follow-up, and proactive optimization—the foundation of preventive medicine and extended healthspan.