Blood drug test: what to know

The test is ordered for a particular question: checking a prescribed medicine level, investigating possible poisoning, assessing an unexplained change in consciousness, or supporting urgent treatment. It does not automatically test for every substance. Results are influenced by when the substance was taken, how the sample was collected, kidney and liver function, other medicines, and the laboratory method. A result needs interpretation alongside symptoms and examination. Conditions such as Chronic Kidney Disease can change how some medicines leave the body, while Anaemia or Coeliac Disease may require separate blood tests.

Give an accurate list of prescribed medicines, non-prescription products, supplements, and any substance taken, including the approximate time. Do not stop a prescribed medicine just to alter a result unless the prescriber instructs you. Ask whether the sample should be taken before or after a scheduled dose. If the test follows a possible overdose or accidental ingestion, take the packaging with you and seek urgent help rather than waiting for an appointment.

Call emergency services for severe sleepiness, confusion, seizures, collapse, slow or difficult breathing, chest pain, or sudden agitation after taking a medicine or substance. Do not make someone vomit and do not give food or drink to a person who is drowsy or unconscious. A blood test can support care, but it should not delay emergency treatment.

Ask what substances the test covers, why it was requested, when the sample should be taken, whether a repeat or confirmatory test is needed, and how the result could affect your medicines. Ask who will explain the result and what symptoms should prompt urgent care.