Answering Common Toxic Metal Testing Questions – What Does Heavy Metal Testing Evaluate?

“All things are poison, and nothing is without poison; the dosage alone makes it so a thing is not a poison.”

—Paracelsus, 1538

As a Medical Education Specialist at a functional medicine lab, I frequently speak with clinicians about how to measure and interpret toxic metal results in patients. There are many tests for metals, including urine, blood, hair, nails, and stool. Which is best? What do the results indicate? Each metal and each sample type have many nuances, so there are no generic answers to these questions. Understanding each sample type, exposure time frame, and clinical questions to be answered can help guide testing.

Why Test for Heavy Metals?

Environmental medicine explores the connections between environmental toxicants and human health. Toxicologists study acute effects and poisoning, while relatively little is known about the long-term effects and the accumulation of toxins.¹ This results in an underdiagnosis of heavy metal toxicity.

Functional medicine clinicians working with complex chronic illnesses focus on identifying the root causes. When major factors have been addressed – diet, lifestyle, conventional laboratory testing, etc. – if symptoms persist, clinicians search for “hidden” causes. Functional medicine clinicians take into account the synergism of the total load of toxicants as a potential causative factor in illness.¹

Heavy metals contaminate the air, water, and food, and some occupations have an increased risk for exposure and toxicity.² For example, we often see elevated lead levels in patients who work in the military or law enforcement because of exposure to lead bullets at practice shooting ranges. “Priority metals” of public health significance include arsenic, cadmium, chromium, lead, and mercury.³

Heavy metal exposure generates reactive oxygen species (ROS) causing cellular toxicity and carcinogenicity.³ Epidemiological studies have linked heavy metal exposure to diabetes, kidney disease, degenerative neurological conditions, cancer, and skin, respiratory, reproductive, and cardiovascular diseases.^2,4 Lead and cadmium chelation is an effective treatment for certain cardiovascular diseases.⁵ Toxic metal removal can be a useful tool in preventing the onset or progression of many diseases associated with metal intoxication.¹

Diagnosing Metal Toxicity

Heavy metal toxicity depends on factors including the dose, duration of exposure, route of exposure, chemical species, age, body weight, genetics, nutritional status, and a combination of metals.^2,3 Signs and symptoms vary depending on the metal and can be due to acute exposure to large amounts or chronic exposure to repeated small amounts, resulting in cumulative toxicity.² Symptoms associated with acute poisoning can differ from chronic poisoning.⁶

A diagnosis of metal toxicity requires 3 factors: (1) elemental source, (2) signs and symptoms typical of the element, and (3) elevated element concentrations.⁷ Depending on your location or patient population, you’re less likely to encounter acute poisoning situations, which typically have a more dramatic presentation. Confirming the diagnosis of chronic metal toxicity is challenging as the signs and symptoms are similar among many chronic diseases.

Taking a detailed medical and occupational/environmental history is a fundamental step. An environmental history intake questionnaire can help identify exposure type and timing, and physical exam findings can also help determine the exposure type.

Conservative recommendations include only testing for the suspected toxicant versus a “shotgun” approach for a variety of toxicants.^8,9 However, functional medicine laboratories often offer panels to test several metals simultaneously.

Sample Types for Metal Testing

When metals enter the circulation, they are either excreted or stored in tissues, contributing to the body burden. Testing cannot distinguish whether the source is a recent exogenous exposure or endogenous exposure from stored metal released from body tissues, with a few exceptions. This is why a detailed history is important. An example of endogenous exposure is increased lead levels from bone turnover during menopause.^6,10 Depending on the metal and the person’s detoxification capacity, some compounds are cleared rapidly while others can persist for years.⁸

Metal levels vary over time because of the variability in diet, lifestyle, and daily activities of the person and by the kinetics of absorption, distribution, metabolism, half-life, and elimination of the metal. One study showed high variability in urinary metals over a 3-month timeframe, suggesting that a single measurement only provides a brief snapshot of the exposure level and may not provide accurate estimates of individual exposures over weeks or months.¹¹ Serial measurements may be more important to assess the risk of ongoing or chronic exposure.

Blood

Blood testing indicates acute and chronic exposure.^2,7  Whole blood is considered the standard assessment for acute metal poisoning, and toxicity cutpoints are based on workplace standards set by the Occupational Safety and Health Administration (OSHA).¹ The exposure timeframe varies depending on the metal. Lead has a half-life in the blood of about 1 to 2 months, and cadmium about 3-4 months. Blood is not useful for identifying arsenic exposure due to the rapid circulation and distribution to tissue storage sites.⁷

Urine

Urine testing indicates both recent exposure and the ability to metabolize and excrete metals.¹ The exposure timeframe varies depending on the metal. For example, arsenic is excreted for 2-4 days post-exposure, 1-3 months for mercury, and 2 months for thallium.⁷ Cadmium has a long half-life of 10-30 years and is stored in the liver and kidneys.^11,12 Urinary cadmium reflects body burden and chronic exposure. Urinary levels do not rise significantly with recent exposure; blood cadmium can confirm recent acute exposure.^13,14 90% of methylmercury (found in fish) is excreted through stool, so urine testing for mercury will only reveal inorganic and elemental mercury. Blood is better for detecting methylmercury excess.⁷ Avoiding seafood before urine testing can help distinguish organic arsenic (from seafood), which is relatively nontoxic, from inorganic arsenic.

Urine can be measured as a first-morning void (FMV), spot urine, or 24-hour urine collection. A 24-hour urine collection has been considered the “gold standard” for assessing metal exposure, although moderate to good correlation is found between spot or FMV urine and 24-hour urine for certain metals. Creatinine-corrected values are important for standardization and to control for urinary dilution.^11,15

Hair and other sample types

Hair analysis represents metal exposure and excretion during the time of hair growth and can represent months to years since exposure.¹⁶ Hair metal analysis is controversial.¹⁷ Methodologies vary among laboratories, and there is no agreed-upon standard for sample preparation to account for external contamination such as metals in hair products. In the 1999 to 2000 National Health and Nutritional Examination Survey (NHANES), hair mercury levels were reported and are available for comparison with individual findings.¹⁸ Hair may not correlate with body burden or clinical signs and symptoms.¹⁴

Other detection methods include nail clippings and stool analysis. These sample types represent current exposure. Stool analysis includes dietary ingested sources as well as metals excreted through bile.

What do the reference ranges mean?

Every lab must validate reference ranges. You should ask the labs about their reference ranges and reference populations. Conventional laboratories may use validated data from the literature and national organizations such as the CDC for accepted values. Functional medicine laboratories may also use these values or may establish a range using a qualified “healthy” cohort. A reference range can be based on an average in the general population, like NHANES. This database shows background levels in the U.S., to which you can compare your patient.⁸ Even though an average concentration in the general population may be deemed “normal,” this doesn’t mean that these levels are without potential health consequences, especially considering it can take years to decades for chronic diseases like cancer to develop. Conversely, an elevation doesn’t automatically correlate with symptoms or constitute toxicity.

Guidelines are well established for some metals, like lead, and less for others. Some metals have critical thresholds indicating a health risk that are reported to health departments. Using lead as an example, a venous blood level of 3.5 mcg/dL for children is the reference range set by the CDC and is based on the 97.5^th percentile using NHANES data. The CDC states that this is not a health-based standard or a toxicity threshold and that no safe level of lead is identified in children. The CDC’s recommended action steps vary based on cutpoints.¹⁹

The proper standards (if they exist) should be consulted for each metal for environmental and/or occupational exposure. OSHA and EPA frequently revise their standards for permissible exposure limits.⁷ For the vast majority of substances, it is not known what levels are associated with health effects; finding a measurable amount of a chemical or toxic metal does not mean it will cause a health problem.⁸

As Paracelsus stated, the dosage alone makes it a poison. That poisonous level can differ from person to person depending on detoxification capacity and other toxin burdens.

Chelated or Provoked Urine Testing

Many clinicians want to assess body burden, meaning the total accumulated amount of metal stored. Chelating agents such as dimercaptosuccinic acid (DMSA), dimercaptopropanesulfonic acid (DMPS), dimercaptopropanesulfonate (DMPS), and ethylenediaminetetraacetic acid (EDTA) are often used as provoking agents, each having a different affinity for certain metals. It’s important to be trained in chelation as it can have adverse effects like increasing the elimination of essential minerals and promoting organ redistribution of metals.⁹

Reference values represent baseline levels of metals in non-chelated samples. No established “normal” reference values exist for post-challenge urine metal testing.⁹ In many instances, chelated metal levels exceed those found in non-chelated samples, and it is not recommended to interpret the results within the context of a non-chelated reference range.

There is no standard, validated challenge test guideline, and conservative organizations such as the American College of Medical Toxicology recommend against it.^20,21 Some studies have shown that challenge testing is not useful for quantifying past exposure.²⁰ Asymptomatic people have shown elevations on provoked testing compared to baseline.^20,21

However, clinicians who do choose to do a provoked test gain the most information from doing two tests. First, a pre-provocation test reflects the current exposure level. A post-provocation test is administered soon after to ensure the patient is not exposed to metals in the interim. A 6-hour post-provocation urine collection is most common; however, some choose 8-, 12-, or 24-hour collections. The difference between the pre- and post-provocation metal levels can reflect body burden, or metals that were pulled endogenously from storage in the body’s tissues, versus current transient exposure.¹

Key Considerations

• It’s important to always look at any lab value in the context of the clinical picture.
• Elevated levels do not automatically imply poisoning or toxicity—this is a clinical determination.
• Metal testing indicates relatively current versus long-ago exposure for any sample type, with a few exceptions.
• With elevated levels, identify the source and avoid continued exposure.
• It’s recommended to complete advanced chelation training before attempting to do provoked urine testing or using chelation therapeutically.
• If there is increased exposure, it would be reasonable to ensure the body’s inherent detoxification capacity is optimized through nutritional support.

Helpful Resources

Organizations like American College for Advancement in Medicine offer chelation training.

The Agency for Toxic Substances and Disease Registry (ATSDR) has an A-Z index of common toxicants and their effects. This can be helpful when determining which sample type to use.

The CDC National Report on Human Exposure to Environmental Chemicals or Canadian Biomonitoring Dashboard have biomonitoring data tables with population reference values for many toxicants.

There are many environmental exposure questionnaires online that can be used in practice. The book in the first reference below includes a questionnaire in the appendix.

 

References:

1. Crinnion W, Pizzorno, J. Clinical Environmental Medicine: Identification and Natural Treatments of Disease Caused by Common Pollutants. Elsevier; 2019.
2. Rajkumar V, Lee VR, Gupta V. Heavy Metal Toxicity. StatPearls Publishing Copyright © 2025, StatPearls Publishing LLC.; 2025.
3. Tchounwou PB, Yedjou CG, Patlolla AK, Sutton DJ. Heavy metal toxicity and the environment. Experientia supplementum (2012). 2012;101:133-164.
4. Martinez-Morata I, Schilling K, Glabonjat RA, et al. Association of Urinary Metals With Cardiovascular Disease Incidence and All-Cause Mortality in the Multi-Ethnic Study of Atherosclerosis (MESA). Circulation. 2024;150(10):758-769.
5. Ravalli F, Vela Parada X, Ujueta F, et al. Chelation Therapy in Patients With Cardiovascular Disease: A Systematic Review. Journal of the American Heart Association. 2022;11(6):e024648.
6. Manocha A, Srivastava LM, Bhargava S. Lead as a Risk Factor for Osteoporosis in Post-menopausal Women. Indian journal of clinical biochemistry : IJCB. 2017;32(3):261-265.
7. Fisher RM, Gupta V. Heavy Metals. StatPearls Publishing Copyright © 2025, StatPearls Publishing LLC.; 2025.
8. Zajac L, Johnson SA, Hauptman M. Doc, can you test me for “toxic metals”? Challenges of testing for toxicants in patients with environmental concerns. Current problems in pediatric and adolescent health care. 2020;50(2):100762.
9. American College of Medical Toxicology position statement on post-chelator challenge urinary metal testing. Journal of medical toxicology : official journal of the American College of Medical Toxicology. 2010;6(1):74-75.
10. Campbell JR, Auinger P. The association between blood lead levels and osteoporosis among adults–results from the third national health and nutrition examination survey (NHANES III). Environmental health perspectives. 2007;115(7):1018-1022.
11. Wang YX, Feng W, Zeng Q, et al. Variability of Metal Levels in Spot, First Morning, and 24-Hour Urine Samples over a 3-Month Period in Healthy Adult Chinese Men. Environmental health perspectives. 2016;124(4):468-476.
12. Fatima G, Raza AM, Hadi N, Nigam N, Mahdi AA. Cadmium in Human Diseases: It’s More than Just a Mere Metal. Indian journal of clinical biochemistry : IJCB. 2019;34(4):371-378.
13. Adams SV, Newcomb PA. Cadmium blood and urine concentrations as measures of exposure: NHANES 1999-2010. Journal of exposure science & environmental epidemiology. 2014;24(2):163-170.
14. ATSDR. Cadmium Toxicity Clinical Assessment – Laboratory Tests. Environmental Health and Medicine Education 2008; https://www.atsdr.cdc.gov/csem/csem.asp?csem=6&po=15 2020.
15. Gaitens JM, Brown CH, Strathmann FG, et al. The Utility of Spot vs 24-Hour Urine Samples for Metal Determination in Veterans With Retained Fragments. American journal of clinical pathology. 2021;155(3):428-434.
16. Ozbek N, Baysal A. Determination of sulfur in human hair using high resolution continuum source graphite furnace molecular absorption spectrometry and its correlation with total protein and albumin. Spectrochimica Acta Part B: Atomic Spectroscopy. 2017;130:17-20.
17. ATSDR. Hair Analysis Panel Discussion: Section 4.1. Summary Report Hair Analysis Panel Discussion Exploring the State of The Science 2001; https://www.atsdr.cdc.gov/hac/hair_analysis/4.1.html, 2025.
18. McDowell MA, Dillon CF, Osterloh J, et al. Hair mercury levels in U.S. children and women of childbearing age: reference range data from NHANES 1999-2000. Environmental health perspectives. 2004;112(11):1165-1171.
19. CDC. CDC Updates Blood Lead Reference Value. Childhood Lead Poisoning Prevention 2024; https://www.cdc.gov/lead-prevention/php/news-features/updates-blood-lead-reference-value.html, 2025.
20. Ruha AM. Recommendations for provoked challenge urine testing. Journal of medical toxicology : official journal of the American College of Medical Toxicology. 2013;9(4):318-325.
21. Hoet P, Haufroid V, Lison D. Heavy metal chelation tests: the misleading and hazardous promise. Arch Toxicol. 2020;94(8):2893-2896.