Urinary Porphyrin Profile: A Quantitative and Qualitative Laboratory Indicator of Mercury Toxicity
by John Wilson, MD
Physicians experienced in mercury detoxification have long been in need of reliable laboratory markers that quantitatively and qualitatively determine which individuals are mercury toxic. Identification of the endpoint of mercury detoxification has also long been in need of objective laboratory markers. Urinary Porphyrin Profile, a relatively new test on the market, can objectively quantify how mercury-toxic a patient is and also help determine when a patient is “cleaned up” from their body burden of mercury.
Prior to the availability of this test, physicians could look at the excretion of mercury in the urine following a chelation challenge test with DMPS or DMSA. However, because of the ability of mercury to “hide” in the body, the amount of urinary excretion of mercury may not always be a reliable measurement of persistent body burden.
Porphyrins are organic ring-shaped structures required in the synthesis of heme, a molecule necessary in the formation of hemoglobin, the iron chelate in red blood cells that transports oxygen in the body. Numerous steps are involved in the pathways that result in porphyrin ring formation, and each step is dependent upon specific enzymes. Porphyrins are formed from coproporphyrin, which in turn forms pre-copropophyrin. All three of these porphyrin compounds are excreted in the urine. Measuring the ratios between the coproporphyrin and the pre-coproporphyrin relative to the porphyrin levels in the urine reveals if the conversions of these precursors are blocked on their way toward porphyrin synthesis. Elevated ratios of coproporphyrin/ porphyrin or pre-coproporphyrin/ porphyrin indicate that the enzymes performing these conversions are impaired. While these enzymes can be genetically impaired, they are sensitive to the toxic effects of mercury, and to a lesser extent other toxic metals as well as xenobiotics (toxic foreign chemicals). This urinary assay is thought to be more suggestive of mercury toxicity because mercury is highly toxic at nanomolar concentrations relative to the other toxic metals.
This is a useful test to identify the end-point of mercury chelation. Urinary porphyrin tests that start off showing impaired enzyme function, and subsequently, following detoxification of mercury, show restored enzyme function, suggest that mercury levels have dropped to a point at which the enzymes are functioning again for that patient.
“Soft” laboratory markers of mercury toxicity include depressed white blood cell count and slightly elevated albumin, but such markers are not specific to mercury. Findings of mercury toxicity on a physical exam will include the presence of mercury amalgams, vermicular fasciculations of the tongue, a crimson stripe on the soft palate margin that fades toward the midline, a one-beat unsustained clonus at the ankles, hypo- or hyper-active distal tendon reflexes, and impaired balance testing. One of the common clinical findings of mercury toxic autistic children is a very pale complexion and attendant anemia, likely related to impaired hemoglobin and porphyrin synthesis. No clinical findings are specific to mercury. Also, since nerve tissue regenerates slowly, these markers become useless as a means of determining when one should stop chelation.
More definitive laboratory markers include tissue specific antibodies to chromatin, fibrillarin, myelin basic protein, chromatin, neurofilaments, and tubulin, with the latter two more likely suggestive of mercury damage. All of these components are found in nerve tissue which, if damaged by mercury (and/or other toxins), will be released into the blood stream, will be “seen” by the immune system, and antibodies specific to these components will thus be produced. Even so, elevated antibodies against these tissues can persist longer than a year even when the body burden of mercury has been sufficiently reduced.
Until recently, the only lab that performed this assay was in France. However, Metametrix Clinical Laboratory in Georgia and Great Plains Laboratory in Kansas now offer this assay, and perhaps others I am not yet aware of. It’s prudent to ask the laboratory to provide you with their controls for this assay. Certified labs in the United States are required to perform and maintain adequate controls on their tests. I am not aware whether such criteria are required for foreign labs. I periodically send split samples to any laboratory that I use to help assure consistency in reporting.
Note: A clear exposition of the biochemistry of porphyrins and the effect of toxic metals on them can be found, courtesy of Metametrix Laboratory, at “Porphyrins White Paper.”
