In suspected lead poisoning, besides measuring whole blood lead, which tests may be useful?

• A. Urine delta-aminolevulinic acid and zinc protoporphyrin
• B. Serum ferritin
• C. Serum copper
• D. Urine arsenic

Answer: (A)

Lead disrupts heme synthesis, so in suspected exposure it helps to look for markers of this disruption in addition to the blood lead level. Urinary delta-aminolevulinic acid rises when ALA dehydratase is inhibited by lead, reflecting accumulation of ALA in the pathway. Zinc protoporphyrin increases because ferrochelatase is inhibited, preventing iron from being inserted into protoporphyrin and causing zinc to be incorporated instead. Together, elevated urinary ALA and increased zinc protoporphyrin indicate impaired heme production consistent with lead exposure and can aid diagnosis and assessment of exposure.

The other tests don’t target the effects of lead on heme synthesis: serum ferritin reflects iron stores rather than lead exposure, and can be influenced by inflammation; serum copper is not a marker of lead effects; and urine arsenic assesses arsenic exposure rather than lead.