Amyloidosis is a group of conditions characterized by the accumulation of amyloid deposits in various tissues. Among these disorders, ATTR amyloidosis occurs either with or without a TTR pathogenic variant. Treatment for amyloidosis depends on the subtype, which is often identified through a tissue biopsy followed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Genetic testing may be done to confirm these results for patients with ATTR amyloidosis; however, the necessity of genetic testing after LC-MS/MS has not been evaluated. A retrospective review identified 153 patients diagnosed with biopsy-proven ATTR amyloidosis, and 56 of these patients underwent both genetic testing and LC-MS/MS. LC-MS/MS and proteomics correctly reported the mutant peptide and heterozygosity in 47/56 (84%) cases. It failed to identify two individuals who were homozygous for the ATTRV122I mutation and failed to detect the following mutations in six other individuals: ATTRA19D, ATTRF44L, ATTRT60A, ATTRI68L and ATTRV122I. Therefore, LC-MS/MS is not sufficient to rule out a pathogenic mutation in cases of ATTR amyloid, and genetic testing should be performed in most cases of ATTR amyloidosis. Correct recognition of hereditary ATTR amyloidosis is important for estimating prognosis, proper familial counselling and guiding use of therapies, such as liver transplantation.