Metals – Current Approaches to Interpreting Results

1. Metals – Current Approaches to Interpreting Results Chris Martin, MD, MSc, FRCPC Associate Professor and Director Institute of Occupational and Environmental Health West Virginia University School of Medicine Morgantown, West Virginia cmartin@hsc.wvu.edu

2. Interpretation of Labs • Clinically apparent metal toxicity is very uncommon in North America • Abnormal measurements in labs are not! • Ordered by someone who doesn’t know what they are doing and performed by a routine lab • Performed by an un$crupulou$ lab • Correct interpretation requires attention to test performance

3. Outline • Background • Properties of tests • On “heavy metals” • How to interpret lab results through 7 sequential steps • You will become a certified MRO • Five case discussions

4. Properties of Tests Accuracy – how close the measurement is to the true value Reliability – consistency on repeat measurements Precision – this relates to the limit of detection of the test Validity – whether the test measures what it purports to measure

6. Precision • The detection limit is the lowest value that can be measured by a test.

7. Detection Limits • Accuracy declines as measured values approach the detection limit of the test • Example consider using the ruler to measure • The width of a femur on an x-ray • The width of a hair

8. Validity Many elements can be measured in hair Does not mean the person has toxic levels of these elements.

9. Definitions • ‘Metals’ originally included only gold, silver, copper, iron, lead, and tin. • Dense, malleable, lustrous • Conduct heat and electricity, cations • Many other elements since added to the list with some of these characteristics • ‘Metalloids’ are elements with features intermediate between metals and non-metals. Example: arsenic

11. ‘Heavy metal’ A metal having an atomic weight greater than sodium, a density greater than 5 g/cm3 Some notion of toxicity Usually includes lead, cadmium and mercury Many others may variably be added to list

12. Correct use of ‘heavy metal’

13. Issues in Interpretation Ask seven questions in order. If each issue cannot be satisfactorily addressed, result is not interpretable and no conclusions can be drawn In general (with exception of lead, mercury, cadmium), measurements over-utilized, raise more questions than are answered

14. Case 1 Manganese

15. Case 1 37-year-old man employed in metallizer operation. Vague respiratory symptoms and headache. Has submitted a workers’ compensation claim for “manganese poisoning”.

16. First Sample: Manganese, plasma 7.2 mcg/L H Normal: < 2.5 mcg/L Limit of Detection = 2.5 mcg/L Additional Notes: “One serum tube pored off from royal blue (sic)”. Second Sample: Manganese, plasma 4.4 mcg/L H Third Sample (after referral to specialist): Manganese (B) 6.0 mcg/L Reference range: 4-14

17. 1. Is measurement meaningful? Beware essential trace elements (zinc, copper, manganese etc.) Labs can (and will) measure them Interpretation problematic for exposure purposes Example: Zinc usually measured in serum

20. Serum zinc Probably falls in setting of symptomatic overexposure (metal fume fever) Non-specific inflammatory response (Serum zinc falls in acute MI.)

21. 2. Is it measured in the correct medium? Urine – 24 hour collection ideal, measure and correct for renal clearance by specific gravity or creatinine clearance Whole blood – collect with anticoagulant Plasma – collect with anticoagulant, spin down promptly to collect supernatant Serum – collect without anticoagulant, allow to clot, spin down to collect supernatant

22. 2. Is it measured in the correct medium? • Serum and plasma not interchangeable • serum levels may be higher than plasma due to invisible hemolysis for elements found at higher concentrations in RBC’s (zinc, manganese)

23. Hair Analysis Many metals (As, Pb, Cr, Cd) incorporated into keratin through binding with sulfhydryl groups

24. Hair Analysis • Pros: • Less invasive • Provides longer-term exposure data

25. Hair Analysis • Cons: • External contamination due to adsorbed material • Great variability in measured values • Little to no reference data • What is the denominator? • Hair growth rate varies with gender, age, body location, season.

26. 2. Is it measured in the correct medium? • Not all metals equal! Example: • Exposure and toxicity from tetra-alkyl lead better reflected in urine measurements • Exposure and toxicity from inorganic lead better reflected in whole blood measurements

27. 3. Could there be contamination? • Recall: levels are often present in “trace” amounts • Collect in trace-element free tube • Know your lab • All glassware must be washed and properly stored, etc. etc.

28. Case 2 Cadmium

29. Case 2 45-year-old male paint technician whole blood cadmium of 5.9 µg/L OSHA biological limit for workers: ≤5.0 µg/L 2000 - 2003, cadmium level 3.1 to 4.3 µg/L. He was medically removal from work with cadmium.

30. Case 2 Blood cadmium 6.1 µg/L seven weeks later. Smokes 1.5 to 2 packs of cigarettes daily for 23 years No additional non-occupational exposures to cadmium were identified. No elevation in urine cadmium, urine β-2 microglobulin, blood creatinine or urea

31. 4. Non-occupational sources?

32. 5. Half-life? • Not a concern for lead and cadmium • Half-life for any metal also varies by medium • Example: mercury

33. Case 3 Mercury

34. Case 3 49-year-old nurse with persistently elevated urine mercury levels. Concerned she has chronic mercury poisoning from numerous dental amalgams, no other exposures identified. Polymyalgia rheumatica and hypertension. Recommended urgent replacement of all mercury amalgam fillings (cost = $5000) followed by IV chelation therapy.

35. Case 3 MERCURY, URINE Mercury, conc < 10 nmol/L Mercury, total H 55 [0-50] nmol/L MERCURY, URINE Mercury, conc 10 nmol/L Mercury, total H 54 [0-50] nmol/L

36. 6. Detection Limit? The lowest amount that an analytical method can measure Good labs don’t report “0” Report should specify detection limit Accuracy of measurement declines as detection limit is approached

37. Case 4 Mercury (Again)

38. Case 4 • 53-year-old lab technician told she may have been exposed to mercury from microscope • No signs or symptoms of mercury toxicity • Random urine reported 33.4 nmol/L (high) • Reference range 0-15 nmol/L • Extensive IH survey of lab reveals air and spot check samples below detection limit during operation of microscope

39. Where did this reference range come from? Lab cites: Brodkin E, Copes R, Mattman A, Kennedy J, Kling R and Yassi A. Lead and mercury exposures: Interpretation and action. CMAJ 176(1):59-63.

40. Where did this reference range come from? These authors in turn, cite data from NHANES. They clearly indicate that cutoff was 95%ile and that investigation for possible exposure should not occur until values are 5x that level Pre-shift limit < 250 nmol/L (FIOH) Lab: We rely on MD to interpret results in context.

41. 7. What is the reference range?

42. ‘Normal’ Ranges • Normal ranges are what we usually deal with in medicine • Derived from large numbers of measurements on healthy people from general population • Determine upper and lower limits based on 2 standard deviation from mean • Consistent between labs • A value outside of range is “abnormal” (although will occur in 5% of healthy people)

43. ‘Reference’ Ranges • Apply to most metal measurements (except lead, cadmium, mercury) • Limited data from small, convenience sample either from published study or lab’s own experience • Usually not occupationally exposed • Inconsistent

44. ‘Reference’ Ranges Upper limit based on highest measured value May also have extremely limited data on massively overexposed cases, these levels may be orders of magnitude higher Unclear what intermediate levels mean

45. Nutrition versus Toxicity • Example - Manganese: • Nutrition Board of the National Research Council’s ESADDI (Estimated Safe and Adequate Daily Dietary Intake) = 2-5 mg day. • EPA’s LOAEL (lowest-observable-adverse-effect level) for water is 4.2 mg day for a 70-kg individual. (Source: Greger JL. J Nutr 1998 Feb; 128 2Suppl:368S-371S)

46. ‘Reference’ Ranges • NHANES provides data on ‘normal’ ranges for: • Lead • Cadmium • Mercury

47. Case 5 Lead

48. Case 5 32-year-old man two-week history of irritability, diffuse myalgias, and arthralgias. Torch cutting of painted bridge beams with inadequate respiratory protection Whole blood lead = 6.4 μmol/L (132.8 μg/dl) Physical exam showed brisk reflexes Other labs normal (including ZPP) except…..