An initial toxicology report for Sandra Bland, the woman who died in jail in Waller County, Tex., on July 13, showed that she had marijuana in her system after her death, but the document does not offer an accurate reading of just how much was circulating in her blood when she died.

When a death is suspicious, sudden or unexpected, toxicology reports are not uncommon.

Ms. Bland had 18 micrograms per liter of T.H.C., the main psychoactive ingredient in marijuana, in her blood, according to a post-mortem report issued Monday. “In a living person, 18 micrograms per liter of T.H.C. is considered elevated, but she is not alive,” said Dr. Nikolas P. Lemos, the chief forensic toxicologist at the Office of the Chief Medical Examiner in San Francisco.