Heavy Metal Scrn w/Rflx Fract, URN (Sendout)

Useful For: Detecting arsenic, cadmium, mercury, and lead exposure and toxicity in 24-hour urine specimens.

Test Algorithm: If arsenic concentration is greater than or equal to 10 mcg/L, then arsenic speciation will be performed at an additional charge.

Interpretation:

Arsenic: Mayo Clinic uses the American Conference of Governmental Industrial Hygienists (ACGIH) biological exposure index (BEI) as the reference value. The BEI is the sum of all the toxic species (inorganic arsenic plus methylated arsenic metabolites).

Physiologically, arsenic exists in a number of toxic and nontoxic forms. The total arsenic concentration reflects all the arsenic present in the sample regardless of species (eg, inorganic vs. methylated vs. organic arsenic). The measurement of urinary total arsenic levels is generally accepted as the most reliable indicator of recent arsenic exposure. However, if the total urine arsenic concentration is elevated, arsenic speciation must be performed to identify if it is the toxic forms (eg, inorganic and methylated arsenic forms) or the relatively nontoxic organic forms (eg, arsenobetaine and arsenocholine).

The inorganic toxic forms of arsenic (eg, As[III] and As[V]) are found in the urine shortly after ingestion, whereas the less toxic methylated forms, monomethylarsinic acid (MMA) and dimethylarsinic acid (DMA), are the species that predominate longer than 24 hours after ingestion. In general, urinary As(III) and As(V) concentrations peak in the urine at approximately 10 hours and return to normal 20 to 30 hours after ingestion. Urinary MMA and DMA concentrations normally peak at approximately 40 to 60 hours and return to baseline 6 to 20 days after ingestion.

After a seafood meal (seafood generally contains the nontoxic, organic form of arsenic (eg, arsenobetaine), the urine output of arsenic may increase to over 300 mcg/24-hr, after which it will decline.

This test can determine if the patient has been exposed to above-average levels of arsenic. It cannot predict whether the arsenic levels in their body will affect their health.

Cadmium: In chronic cadmium exposure, the kidneys are the primary target organ. Urine concentrations of cadmium can be useful to assess long-term exposure and determine cadmium body burden. Collection of urine over 24 hours minimizes fluctuations of observed cadmium concentrations in random urine samples.

Cadmium excretion above 3.0 mcg/g creatinine indicates significant exposure to cadmium. For occupational testing, OSHA cadmium standard is less than 3.0 mcg/g creatine and the BEI is 5 mcg/g creatinine.

Mercury: Daily urine excretion of mercury above 50 mcg/day indicates significant exposure (per World Health Organization standard).

Lead: Measurements of urinary lead (Pb) levels have been used to assess lead exposure. However, like lead blood, urinary lead excretion mainly reflects recent exposure and thus shares many of the same limitations for assessing Pb body burden or long-term exposure.¹

Urinary lead concentration increases exponentially with blood lead and can exhibit relatively high intra-individual variability, even at similar blood lead concentrations.¹

Cautions:

Consumption of seafood before collection of a urine specimen for arsenic testing is likely to result in a report of an elevated concentration of arsenic found in the urine, which can be clinically misleading.

Collection of urine specimens through a catheter frequently results in elevated values because rubber contains trace amounts of cadmium that are extracted as urine passes through the catheter.

To avoid contamination by dust, specimen should be collected away from the site of suspected exposure.

Patient Preparation:

• High concentrations of gadolinium and iodine are known to interfere with most metals tests. If either gadolinium- or iodine-containing contrast media has been administered, a specimen should not be collected for 96 hours.
• Patient should not eat seafood for a 48-hour period prior to start of, or during, collection.

Collection:

• Collect urine for 24 hours in a preservative-free amber polyethylene 24-hr urine collection container (with no metal caps or glued inserts).
• Refer to Mayo Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for additional information on acceptable collection conditions.
• Refrigerate urine within 4 hours of completion of collection.

Outside Laboratories:

• Mix specimen well. Measure and record total volume. Note the collection interval and total volume on the requisition.
• Aliquot urine into a Mayo metal-free screw-capped vial (T173) and refrigerate.
  • Note: Mayo T173 is recommended, but not required.

Stability: Refrigerated (preferred): 7 days; Frozen: 7 days; Ambient: Unacceptable.

SPS: Specimen must be refrigerated within 4 hours of completion of 24-hour collection.

• Mix specimen well.
• Measure and record total volume.
• Aliquot urine into a Mayo metal-free screw-capped vial (T173) and refrigerate.
  • Note: Mayo T173 is recommended, but not required.

Sendouts:

• Order Mayo Test: HMU24.
• Interfaced: Yes.

Stability: Refrigerated (preferred): 7 days; Frozen: 7 days; Ambient: Unacceptable.