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Blood work

Reference ranges for blood test results vary around the world; they take into account ethnic and genetic differences and are based on statistical data from 95% „healthy“ individuals. 5% therefore fall outside this „normal“ range.

Further parameters such as diet, BMI, age, and gender will be included in the determination of these reference values.

When assessing, in addition to a holistic medical evaluation, it must be considered that measurement methods, equipment calibrations, etc., can also lead to deviations in the values of one and the same sample.

International Valuation

Anyone who looks more closely at their lab results often notices:
„Normal“ blood values are by no means uniformly defined worldwide. A value that is considered unremarkable in Germany may already be considered elevated in Japan or still within the reference range in the USA.

These differences are not a mistake of the laboratories, but the result of decades of scientific development, statistical methods, and population-specific research.

Modern laboratory medicine therefore does not work with absolute universal truths, but with so-called reference intervals, which can vary from country to country, lab to lab, and even between analyzers.

What is a „normal value“?

The term „normal value“ is actually imprecise in a medical context. Technically correct, one speaks of:

• Reference range
• Reference interval
• clinical decision value

Most laboratory test results are statistically based on the 95th percentile of a reference population defined as healthy.

This means:

• The lowest 2.5 % and highest 2.5 % are excluded
• Even healthy people can therefore be outside the „normal range.“
• A „normal“ value doesn't automatically mean optimal health

Reference Ranges – International Comparison

A selection of the most common laboratory parameters in international comparison:

Why are reference ranges internationally different?

The differences arise from several factors simultaneously:

Different population groups

Large international studies show clear differences between populations regarding:

• Muscle mass
• Nutrition
• Body weight
• Ethnic genetics
• Hormone profile
• Inflammatory activity
• Iodine supply
• Alcohol consumption

This shifts the natural distributions of certain laboratory values.

Example – Ferritin

Ferritin is a marker of iron metabolism and is among the most variable reference values worldwide.

Ferritin Men (ng/ml)	Germany/EU	USA	Japan/East Asia
Reference range	30–400	24–336	20–280

While some European laboratories interpret ferritin levels below 30 ng/ml as functional iron deficiency, they are still considered normal in other countries.

The causes:

• different definitions of inflammation
• various reference populations
• statistical analysis methods
• different measuring platforms

Example – Thyroid value TSH

TSH is one of the most controversial lab values of all.

TSH (mIU/L)	Germany/EU	USA	Japan/East Asia
Reference range	0.3–4.0	0.4–4.5	0.5–5.0

Why these differences?

Studies show:

• Age strongly influences TSH
• Iodine supply changes average values
• Autoimmune diseases shift populations
• Ethnicity plays a role

Some endocrinologists therefore argue:

• Values over 2.5 are already noticeable

Other professional societies, however, warn against overdiagnosis.

Example – Liver Values (ALT/GPT)

Liver values show particularly clearly how much modern lifestyle habits can change reference ranges.

ALT/GPT Men (U/L)	Germany/EU	USA	Japan/East Asia
Upper limit	Under 45	Under 40	30–35

Historically, many reference ranges were created from populations where:

• Overweight
• Alcohol consumption
• Fatty liver
• metabolic syndrome

already occurred frequently.

This caused the „normal ranges“ to be artificially shifted upwards in part.

Recent Asian studies therefore use stricter upper limits to detect early liver disease sooner.

Example - Vitamin D

Vitamin D impressively shows how differently medical professional societies interpret the same data.

Vitamin D (ng/mL)	Germany/EU	USA	Japan/East Asia
Optimal range	30–50	30–60	20–40

Depending on the professional society, the following apply:

• under 20 ng/mL
• under 12 ng/ml
  or even only below 10 ng/ml as a true deficiency

The cause:
different studies assess different health endpoints:

• Bone health
• immune system
• Cancer risk
• Autoimmunity
• mortality

Measuring Devices - Differences

Lab values depend not only on the person, but also on the measurement system used: Different

• Analyzers
• Reagents
• Calibrations
• Laboratory methods

can produce measurable differences. That's why international organizations like IFCC (International Federation of Clinical Chemistry and Laboratory Medicine, CLSI (Clinical and Laboratory Standards Instituteand WHOWorld Health Organizationa local validation of reference intervals.

Laboratory Medicine in Transition

The classic idea of a fixed „normal value“ is increasingly criticized today, as recent research shows that

• People have individual biological baselines.
• values change depending on age
• Averages are not always optimal
• Population-based limits do not consider pre-existing conditions

That's why modern laboratory medicine is moving more towards:

• personalized reference intervals
• AI-powered trend analysis
• individual long-term profiles
• dynamic reference systems

Blood Test Results Explained

Hematology

Hemoglobin (Hb)

Hemoglobin is the iron-containing pigment of red blood cells and transports oxygen in the body.

Humiliated:

• Iron deficiency
• Blood loss
• Vitamin B12 Deficiency
• chronic illnesses

Increased:

• Smoking
• Oxygen deficiency
• Lung diseases
• Dehydration
• rare bone marrow diseases

Hematocrit (Hct) – Percentage of blood cells in the total blood volume

Increased:

• Dehydration
• Polycythemia
• chronic oxygen deprivation

Humiliated:

• Blood loss
• Anemia
• Overwatering

Leukocytes

Leukocytes are white blood cells and are central to the immune system.

Increased:

• Bacterial infections
• Inflammation
• Stress reactions
• Leukemias

Humiliated:

• Viral infections
• Bone marrow damage
• Immunosuppression

Thrombocytes

Platelets are blood cells and important for blood clotting.

Increased:

• Inflammation
• Iron deficiency
• Bone marrow diseases

Humiliated:

• Bleeding tendency
• Autoimmune processes
• Liver diseases

Iron metabolism

Ferritin

Ferritin is the most important storage parameter for iron.

Humiliated:

• Iron deficiency
• chronic blood loss
• Malnutrition

Increased:

• Inflammation
• Liver diseases
• Iron overload
• metabolic syndrome

Ferritin is an acute-phase protein and therefore inflammation-dependent.

iron

Measures the current amount of circulating iron in the blood.

Humiliated:

• Iron deficiency
• chronic illnesses

Increased:

• Iron overload
• Liver diseases
• Hemolysis

The individual value is prone to fluctuations and is not very meaningful on its own.

Electrolytes

Sodium

Regulates water balance, nerve function, and blood pressure.

Humiliated:

• Overwatering
• Heart/kidney failure
• Hormonal disorders

Increased:

• Dehydration
• Diabetes insipidus

Potassium – Heart function, muscles, and nervous system.

Humiliated:

• Arrhythmias
• Muscle weakness
• Diuretics

Increased:

• Kidney failure,
• life-threatening arrhythmias.

Calcium – Bones, Nerves, and Muscle Contraction.

Humiliated:

• Vitamin D deficiency
• Hypoparathyroidism

Increased:

• Hyperparathyroidism
• Tumor diseases

Magnesium – Muscle and Nerve Function.

Deficiency:

• cramps
• Arrhythmias
• Stress reactions

Increased:

• kidney dysfunction

Kidney values

Creatinine

Metabolic byproduct of muscle metabolism; marker of kidney function.

Increased:

• impaired kidney function
• Dehydration

Humiliated:

• low muscle mass

eGFR – Estimated Glomerular Filtration Rate

Humiliated:

• chronic kidney disease
• Kidney failure

Uric acid – end product of purine metabolism

Increased:

• Gout
• metabolic syndrome
• Kidney disorder

Liver function tests

ALT/GPT – Markers for Liver Damage

Increased:

• Fatty liver
• Hepatitis
• Alcohol
• Medication damage

AST/GOT

Found in the liver, heart, and muscles.

Increased:

• Liver cell damage
• Muscle damage
• Heart damage

GGT

Highly sensitive marker for bile ducts and alcohol influence.

Increased:

• Alcohol exposure
• Cholestasis
• Fatty liver

Bilirubin – breakdown product of red blood cells

Increased:

• Jaundice
• Liver disorder
• Gallstones
• Hemolysis

Glucose & Diabetes

Fasting Glucose – Blood Sugar After Fasting

Increased:

• Prediabetes
• diabetes
• Stress reactions

Humiliated:

• Hypoglycemia
• Hormonal disorders

HbA1c – Long-term blood sugar (approx. 8–12 weeks)

Increased:

• chronically elevated glucose
• Diabetes mellitus

Lipid panel

LDL Cholesterol

Transports cholesterol to tissues.

Increased:

• Arteriosclerosis risk
• Cardiovascular diseases

HDL Cholesterol

Transports cholesterol back to the liver.

Humiliated:

• increased heart risk

Triglycerides - the body's storage fats

Increased:

• metabolic syndrome
• diabetes
• Alcohol
• Overweight

Thyroid gland

TSH – Thyroid Stimulating Hormone

Increased:

• Hypothyroidism

Humiliated:

• Hyperthyroidism

fT4 – Free Thyroidroxine

Reflects direct thyroid hormone production.

fT3 – Active Form of Thyroid Hormone

Especially important for:

• Hyperthyroidism
• Conversion disorder

Iodine metabolism

Iodide (Serum)

Iodide is the form of iodine circulating in the blood and is essential for the production of thyroid hormones.

Humiliated:

• Iodine deficiency
• Reduced thyroid hormone production
• Risk of goiter
• Hypothyroidism

Increased:

• excessive iodine intake
• Contrast agent load
• iodine-induced thyroid disorders

However, serum iodide fluctuates relatively strongly and is only suitable to a limited extent for assessing long-term iodine supply.

Iodine excretion in urine

Urinary iodine excretion is considered the most important marker of a population's iodine supply.

Since approximately 90% of the absorbed iodine is excreted in the urine, this provides a relatively good estimate of current iodine status.

Humiliated:

• Iodine deficiency
• Risk of thyroid enlargement
• Hormonal dysregulation

Increased:

• high iodine intake
• Dietary supplement
• Contrast medium
• certain medications

The WHO uses urinary iodine excretion as an international standard parameter for assessing the iodine supply of populations.

Iodine/Creatinine Ratio

This value corrects iodine excretion for creatinine excretion, thereby reducing variations in urine dilution.

It is more accurate than a single measurement of iodine concentration in spontaneous urine.

Thyroglobulin

Thyroglobulin is a protein of the thyroid gland and an indirect marker of iodine supply and thyroid activity.

Increased:

• Iodine deficiency
• Thyroid growth
• Inflammation
• Hyperthyroidism
• Thyroid cancer

In regions with chronic iodine deficiency, thyroglobulin levels are often elevated.

TPO antibodies

TPO antibodies target thyroid peroxidase and are markers of autoimmune thyroid diseases.

Increased:

• Hashimoto's thyroiditis
• Graves' disease
• autoimmune inflammatory processes

Iodine intake indirectly influences TPO antibodies:

• both severe iodine deficiency
• as well as very high iodine intake
  can promote autoimmune reactions.

Iodine Values - International Relevance

Iodine is one of the most geographically diverse nutrients worldwide.

The differences arise from:

• Soil iodine content
• Proximity to the sea
• Using iodized salt
• Eating habits
• Fish consumption
• State-sponsored iodization programs

Examples:

• Japan traditionally has a very high iodine intake due to seaweed consumption
• Germany was historically considered a region with iodine deficiency for a long time.
• The USA is in the middle range due to widespread use of iodized salt

That's why they also differ:

• Reference ranges
• Target values
• clinical interpretation of thyroid parameters is sometimes significantly different internationally

Vitamins & Trace Elements

Vitamin D – Bones, Immune System, Muscle Metabolism

Deficiency:

• Osteomalacia
• Muscle weakness

Vitamin B12

Essential for:

• Nerve
• Blood formation
• DNA synthesis

Deficiency:

• neurological disorders
• Macrocytic anemia

Folic Acid – Cell Division and Blood Formation

Deficiency:

• Macrocytic anemia
• Pregnancy risks

Inflammation & Coagulation

CRP - Acute-phase protein of inflammation

Increased:

• bacterial infections
• Inflammation
• Tissue damage

hs-CRP

High-sensitivity CRP for estimating cardiovascular risk.

INR - International Normalized Ratio

Increased:

• Bleeding tendency
• Marcumar therapy
• Liver disease

D-Dimer – Degradation product of blood clots

Increased:

• thrombosis
• Embolism
• Severe inflammation

Not definitive on its own, but important for excluding thrombotic events.

Closing words

A single blood value alone often does not allow for a definitive diagnosis, as it can be statistically normal, functionally problematic, or clinically irrelevant at the same time.

Therefore, good doctors also always consider the described symptoms, medical history, past and future progression, medication and diet, as well as the patient's ethnicity, age, gender, and athletic status.

Reference ranges are therefore not a law of nature but simply a statistical tool for interpretation by the treating physician.

Dietary supplements

Similar to reference ranges for medical laboratory parameters, information on daily nutritional needs works in a similar way.

While the above laboratory parameters are standardized, there are various designations in the field of dietary supplements (NEMs) to describe the same thing.
The information provided, particularly the „100% daily requirement,“ suggests scientific rigor, but it is based solely on rough estimates derived from statistical data.
Only UL has a certain scientifically founded character that is intended to prevent the occurrence of undesirable effects.

• NRV – Nutrient Reference Value
  Reference amounts valid in the EU for the declaration of nutritional information
  Do not represent individually optimal target values
• RDA – Recommended Dietary Allowance
  As determined by the Institute of Medicine, also known as the National Academies
  Represent the needs of approximately 97–98 % healthy individuals in a population group
• AI – Adequate Intake
  Primarily based on observational data rather than exact needs analyses.
• UL – Tolerable Upper Intake Level
  Maximum safe daily intake for long-term use
  Describes the safety area above which the occurrence of undesirable effects becomes more likely

Added to this is the aspect of bioavailability: if it is only moderately available, a significantly higher dosage would be necessary than with a very well bioavailable product.

For example, magnesium in the forms

• Magnesium citrate → high bioavailability
• Magnesium oxide → lower bioavailability

or regarding Vitamin B12, which is considered

• Methylcobalamin
• Hydroxocobalamin
• Cyanocobalamin

each exhibit different pharmacological properties.

NEMs – Daily Requirements vs. Lab Data

A common mistake is to take supplements based solely on general recommendations, without considering individualized laboratory values, e.g.

• Ferritin,
• Vitamin D,
• B12,
• Homocysteine,
• Magnesium,
• Zinc,
• Selene,
• Jodine status,
• Omega-3 Index.

The „more is better“ approach is therefore incorrect. Also, a normal serum value according to the lab report does not necessarily mean optimal supply, while a low value can already have functional relevance.

International Reference Values / Recommended Daily Allowance (RDA) of Dietary Supplements (DS)

Central Studies & Reference Sources

Sasidharan Sivakumar, Ishika Makhija, Ruchika Bhagat, Saanvi Maurya, Nabendu Sekhar Chatterjee, Savita Bansal, Nilesh Chandra – Ethnicity-Based Variations in Biological Reference Intervals – ScienceDirect – A systematic scoping review (2026)

This large review article shows that ethnic and regional differences have significant effects on reference ranges for numerous laboratory parameters.
The authors particularly criticize the global use of Western reference values for non-Western populations.

Key messages

• Reference ranges are population-dependent
• Western norms are not universally valid
• Genetic and environmental factors significantly influence laboratory values

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Kiyoshi Ichihara, Yesim Ozarda, Julian H Barth, George Klee, Ling Qiu, Rajiv Erasmus, Anwar Borai, Svetlana Evgina, Tester Ashavaid, Dilshad Khan, Laura Schreier, Reynan Rolle, Yoshihisa Shimizu, Shogo Kimura, Reo Kawano, David Armbruster, Kazuo Mori, Binod K Yadav; Committee on Reference Intervals and Decision Limits, International Federation of Clinical Chemistry and Laboratory Medicine – A global multicenter study on reference values: Assessment of methods for derivation and comparison of reference intervals (IFCC) – Clin Chim Acta – April 2017

International IFCC study on harmonizing global reference ranges.
This work is considered one of the most important foundations of modern reference interval research.

Key messages

• Reference values differ significantly between countries
• BMI, Ethnicity, Diet, and Methodology Affect Laboratory Parameters
• Global standardization is difficult

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Nadav Rappoport, Hyojung Paik, Boris Oskotsky, Ruth Tor, Elad Ziv, Noah Zaitlen, Atul J Butte – Comparing Ethnicity-Specific Reference Intervals for Clinical Laboratory Tests – J Appl Med – 11/01/2018

This study used millions of electronic health records (EHRs) to demonstrate ethnicity-specific differences in laboratory values.

Key messages

• significant differences in:
  • Creatinine
  • HbA1c
  • Liver values
  • Hematology parameters
• Universal reference ranges can potentially lead to misclassifications

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Enjung Lim, Jill Miyamura, John J Chen – Racial/Ethnic-Specific Reference Intervals for Common Laboratory Tests – Hawai J Med Public Health – September 2015

Large population-based study from Hawaii with Asian, White, Black, and Hispanic population groups.

Key messages

• clear differences in:
  • Leukocytes
  • Ferritin
  • Creatinine
  • Lipid levels
  • HbA1c
• Ethnicity-specific reference intervals improve diagnostics

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Effect of Ethnicity on Reference Intervals - Clinical Chemistry, Volume 48, Issue 10, 1 October 2002, Pages 1802–1804 – October 1, 2002

Classic foundational work on the question of when different ethnicities require separate reference intervals.

Key messages

• describes statistical criteria for dividing reference groups
• Basis for many current laboratory standards

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Nadav Rappoport, Hyojung Paik, Boris Oskotsky, Ruth Tor, Elad Ziv, Noah Zaitlen, Atul J Butte – Influence of ethnicity on population reference values for biochemical markers – J Appl Lab Med. – Nov 1, 2018

Review of Biochemical Markers and Ethnic Differences.

Key messages

„We found that the distributions of >50% in laboratory tests—which currently have fixed reference intervals—vary among self-identified racial and ethnic groups (SIREs) in healthy individuals.”.

Our results confirm the known SIRE-specific differences in creatinine and suggest that further research is needed to determine the clinical implications of using uniform reference intervals for other tests with SIRE-specific distributions.“