Certainly the “big 3” are important, but other endogenous metabolites may also interfere with common laboratory tests. Among the endogenous interferents, these seven circulate at relatively high concentration and can interfere with spectrophotometric assays: creatinine, glucose, glycerol, lactate, pyruvate, uric acid, and urea. CLSI has recommended concentrations and protocols for testing these potential interferents (Interference Testing in Clinical Chemistry; Approved Guidelines (EP07-A2), and Sun Diagnostics now has a kit to simplify testing for these endogenous metabolites: INT-06. The metabolites come in individual vials at 20-fold the CLSI recommended test concentrations so that they are easily spiked into serum or urine pools for analysis.