Paralytic shellfish toxins in clinical matrices: Extension of AOAC official method 2005.06 to human urine and serum and application to a 2007 case study in Maine

Paralytic shellfish poisoning (PSP), a potentially fatal foodborne illness, is often diagnosed anecdotally based on symptoms and dietary history. The neurotoxins responsible for PSP, collectively referred to as the saxitoxins or paralytic shellfish toxins (PSTs), are natural toxins, produced by certain dinoflagellates, that may accumulate in seafood, particularly filter-feeding bivalves. Illnesses are rare because of effective monitoring programs, yet occasional poisonings occur. Rarely are contaminated food and human clinical samples (e.g., urine and serum) available for testing. There are currently few methods, none of which are validated, for determining PSTs in clinical matrices. This study evaluated AOAC (Association of Analytical Communities) Official Method of Analysis (OMA) 2005.06. [AOAC Official Method 2005.06 Paralytic Shellfish Poisoning Toxins in Shellfish: Prechormatographic Oxidation and Liquid Chromatography with Fluorescence Detection. In Official Methods of Analysis of AOAC International 〈http://www.eoma.aoac.org〉], validated only for shellfish extracts, for its extension to human urine and serum samples. Initial assessment of control urine and serum matrices resulted in a sample cleanup modification when working with urine to remove hippuric acid, a natural urinary compound of environmental/dietary origin, which co-eluted with saxitoxin. Commercially available urine and serum matrices were then quantitatively spiked with PSTs that were available as certified reference materials (STX, dcSTX, B1, GTX2/3, C1/2, NEO, and GTX1/4) to assess method performance characteristics. The method was subsequently applied successfully to a PSP case study that occurred in July 2007 in Maine. Not only were PSTs identified in the patient urine and serum samples, the measured time series also led to the first report of human PST-specific urinary elimination rates. The LC-FD data generated from this case study compared remarkably well to results obtained using AOAC OMA 2011.27 [AOAC Official Method 2011.27 Paralytic Shellfish Toxins (PSTs) in Shellfish, Receptor Binding Assay. In Official Methods of Analysis of AOAC International 〈http://www.eoma.aoac.org〉], further demonstrating successful extension of the LC-FD method to these clinical matrices. Moreover, data generated from this poisoning event reiterated that urine is a preferable clinical matrix, compared to serum, for diagnostic purposes due to higher accumulation and longer residence times in urine.