What is a reference range on a blood test?

A reference range is the interval of values found in 95% of healthy adults. Results outside the range are flagged as high (H) or low (L). Reference ranges differ between laboratories depending on the analyser and method used, so always compare your result to the range printed on your own laboratory report rather than values found online.

How do I read my blood test results?

Each line of a blood test result shows: the test name and abbreviation, your measured value, the unit (e.g. mmol/L, g/dL), and the laboratory's reference range. A flag of H or L beside the result means your value falls outside the reference range. One abnormal result rarely means disease — context, symptoms, and trends over time are what matter.

What are the most commonly ordered blood tests?

The most frequently ordered tests are: CBC (complete blood count) for red cells, white cells and platelets; metabolic panels for kidney and electrolytes; liver function tests (LFTs) for liver health; lipid profile for cardiovascular risk; HbA1c and fasting glucose for diabetes; thyroid function (TSH, T4) for thyroid disorders; and vitamin D and B12 for nutritional status.

Why might a blood test result be falsely abnormal?

Common causes of falsely abnormal results include: not fasting when required (affects glucose, triglycerides), haemolysis during sample collection (artificially raises potassium), dehydration (concentrates all values), medications (steroids raise glucose, diuretics lower potassium), time of day (cortisol peaks in the morning), and laboratory error. Always discuss unexpected results with your doctor before acting on them.

Patient Guide

Blood Tests A to Z: Common Lab Tests Explained

Name: Blood Tests A to Z: Complete Guide to Common Lab Tests
Creator: Suman Konda
Published: 2026-07-05

This A–Z guide covers the most commonly ordered blood tests. Use it to quickly look up what any blood test measures and what your result means.

Written by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

How reference ranges work

Every blood test result is accompanied by a reference range – the interval within which most healthy people fall. These ranges are not arbitrary: they are typically derived from the central 95% of measurements in a healthy reference population, defined using statistical methods recommended by international clinical laboratory bodies.¹ The practical consequence is that 1 in 20 completely healthy people will have at least one result outside the reference range purely by chance. A single mildly abnormal value in an otherwise well person is therefore not automatically cause for concern – context matters as much as the number.

Several factors shift results without implying disease. Age-specific and sex-specific ranges exist for many tests (haemoglobin, creatinine, and several hormones differ between men and women and change across the lifespan). Pregnancy changes reference intervals substantially. Timing matters for hormone tests such as cortisol and testosterone, which peak in the morning. Fasting is required for glucose and lipid profiles. The laboratory performing the test should print its own reference range on the result, since equipment, reagents and local population characteristics can produce slightly different thresholds between institutions. When a result is unexpected, a repeat test after confirming correct preparation is usually the appropriate first step.

The A-to-Z table below lists typical adult ranges and what each test is used for. Use it as a starting point, not a substitute for advice from the clinician who ordered the test.

A

Test	Normal Range	What it measures
Albumin	3.5–5.0 g/dL	Main blood protein; low in liver disease, malnutrition, kidney disease
ALP (Alkaline Phosphatase)	44–147 U/L	Liver/bile duct or bone disease
ALT (Alanine aminotransferase)	7–56 U/L	Liver cell damage: most specific liver enzyme
ANA	Negative / <1:40	Autoimmune screening: lupus, Sjögren's, scleroderma
AST (Aspartate aminotransferase)	10–40 U/L	Liver and muscle damage

B

Test	Normal Range	What it measures
Bilirubin (total)	0.1–1.2 mg/dL	Jaundice: liver, bile duct or haemolysis
BNP / NT-proBNP	BNP <100 pg/mL	Heart failure: stretching of heart chambers
Blood urea / BUN	7–20 mg/dL	Kidney function and hydration status

C

Test	Normal Range	What it measures
Calcium	8.5–10.5 mg/dL	Bone health, parathyroid, kidney, malignancy
CBC / FBC	See individual parameters	Red cells, white cells, platelets: full picture
Cholesterol (LDL)	<100 mg/dL optimal	Heart disease risk: main statin target
CK (Creatine Kinase)	55–170 U/L	Muscle damage: myopathy, rhabdomyolysis
Creatinine	Men: 0.74–1.35 mg/dL; Women: 0.59–1.04 mg/dL	Kidney waste product: rises as kidneys fail
CRP	<10 mg/L	Inflammation: rises quickly with infection or flare

D – G

Test	Normal Range	What it measures
D-Dimer	<0.5 mg/L	Blood clot activity: DVT, PE screening
ESR	Men: <15 mm/hr; Women: <20 mm/hr	Chronic inflammation: slower than CRP
Ferritin	Men: 24–336 ng/mL; Women: 11–307 ng/mL	Iron stores: most sensitive iron deficiency marker
GGT (Gamma-GT)	Men: <71 U/L; Women: <42 U/L	Liver/bile duct + alcohol marker
Glucose (fasting)	70–100 mg/dL	Diabetes screening and monitoring

H – M

Test	Normal Range	What it measures
HbA1c	<5.7% normal; 5.7–6.4% pre-diabetes; ≥6.5% diabetes	Average blood sugar over 3 months
Haemoglobin	Men: 13.5–17.5; Women: 12.0–15.5 g/dL	Oxygen carrier: low = anaemia
HDL Cholesterol	Men: >40 mg/dL; Women: >50 mg/dL	"Good" cholesterol: protective against heart disease
INR	0.8–1.2 (2.0–3.0 on warfarin)	Blood clotting time: liver function and warfarin monitoring
LDH	140–280 U/L	Cell damage: haemolysis, heart attack, cancer
LFT panel	See individual tests	Liver health: enzymes + synthetic function
Magnesium	1.7–2.2 mg/dL	Electrolyte: arrhythmia risk when low

P – Z

Test	Normal Range	What it measures
Phosphorus	2.5–4.5 mg/dL	Bone mineral: rises in kidney disease
Platelets	150,000–400,000/µL	Clotting cells: low = bleeding risk; high = clot risk
Potassium	3.5–5.0 mEq/L	Electrolyte: heart rhythm critical; high dangerous
PSA	<4.0 ng/mL	Prostate cancer screening in men
Sodium	136–145 mEq/L	Fluid balance: hyponatraemia common in elderly
Testosterone (total, men)	300–1,000 ng/dL	Male hormone: low causes fatigue, reduced libido
Troponin	<0.04 ng/mL (varies by lab)	Heart muscle damage: definitive heart attack test
TSH	0.4–4.0 mIU/L	Thyroid function: low in hyperthyroid; high in hypothyroid
Uric Acid	Men: 3.5–7.2 mg/dL; Women: 2.6–6.0 mg/dL	Gout: crystals in joints when high
Vitamin B12	200–900 pg/mL	Nerve and red cell health
Vitamin D (25-OH)	30–100 ng/mL	Bone and immune health
WBC (white count)	4,500–11,000/µL	Immune cells: high = infection; low = marrow/viral
Zinc	70–120 mcg/dL	Immune function, wound healing, taste

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

Ozarda Y. Reference intervals: current status, recent developments and future considerations. Biochem Med (Zagreb). 2016;26(1):5–16. PMID 26981013 · doi:10.11613/BM.2016.001