The fasting requirement survives out of habit. Non-fasting total cholesterol, HDL and calculated non-HDL are all adequate for risk assessment and for monitoring treatment, and every major guideline now accepts them. Triglycerides rise after a meal; total cholesterol and HDL barely move.
The cost of insisting on the fast is not analytical, it is practical. A patient told to return fasting is a patient who may not return. In a clinic where attendance is the rate-limiting step, a sample taken at the visit you already have is worth more than a marginally tidier triglyceride from a visit that never happens.
The exceptions are narrow: a non-fasting triglyceride above about 4.5 mmol/L warrants a fasting repeat, as does investigation of suspected familial hypertriglyceridaemia or monitoring someone on treatment specifically for very high triglycerides. Outside those, take the blood while the patient is in front of you.
- Use non-HDL cholesterol as the working number — it needs no fast and no triglyceride-dependent calculation.
- Repeat fasting only if non-fasting triglycerides exceed about 4.5 mmol/L.
- Order lipids at the same visit as any other bloods rather than scheduling a separate fasting attendance.
- Tell the laboratory the sample is non-fasting so the report is interpreted correctly.
Why it matters
The fasting instruction converts a completed test into a second appointment, and the second appointment is where patients are lost.
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