Why or when did NHS fasting bloods get disc’ed?

Excellent question. The short answer is that fasting for blood tests hasn’t gone out of fashion universally, but the requirement has been significantly relaxed for many common tests due to improved scientific understanding and more precise testing methods.

Here’s a breakdown of why the rigid “fasting for 12 hours” rule has evolved:

1. The Cholesterol (Lipid) Panel Revolution

This is the biggest reason for the change in public perception.

• Old Rule: Strict 8-12 hour fast for a “fasting lipid panel” to measure Total Cholesterol, LDL (“bad”), HDL (“good”), and Triglycerides.
• New Understanding: Large studies (like the 2016 Copenhagen General Population Study) showed that for most people, non-fasting triglyceride levels are just as predictive, if not more predictive, of cardiovascular risk.
• The Shift: Major guidelines from groups like the European Atherosclerosis Society and the American Heart Association now state that non-fasting lipid panels are acceptable for routine screening. LDL can be calculated accurately enough from a non-fasting sample for most individuals.
• Exceptions: Fasting is still recommended for those with very high triglycerides, diabetes, or when a doctor is starting/changing lipid-lowering medication.

Why this changed: Convenience for patients and the realization that we live in a non-fasting state for most of the day, so that measurement is more representative.

2. Advancements in Laboratory Technology

Modern analyzers are more specific and less prone to interference.

• Old Methods: Chemical assays for blood sugar (glucose) could be cross-reactive with other sugars from a recent meal, leading to false highs.
• New Methods: Current enzymatic methods (like hexokinase) are highly specific to glucose. While food still affects glucose levels, the test itself isn’t fooled by other substances.
• Reference Ranges: Labs have developed more accurate reference ranges for non-fasting states for many analytes.

3. The Rise of HbA1c for Diabetes Diagnosis and Monitoring

• Fasting Glucose Test: Requires an 8-hour fast and is a snapshot in time.
• HbA1c Test: Measures average blood sugar over the past 2-3 months. It does not require fasting and is less variable. Its adoption as a primary diagnostic tool reduced the number of mandatory fasting tests.

4. Recognition of the Downsides of Fasting

• Patient Inconvenience & Non-Compliance: Early morning appointments, discomfort, and scheduling difficulties led people to skip tests.
• Dehydration: Prolonged fasting can concentrate the blood, potentially skewing results for some components (like electrolytes and kidney markers).
• Safety: Risk of dizziness, fainting, and hypoglycemia in some individuals.

Tests That STILL Require Fasting (The Exceptions)

Fasting is not obsolete. It is still critically important for:

• Formal Glucose Tolerance Test (GTT): For diagnosing gestational diabetes or pre-diabetes. You must fast, then drink a sugary solution.
• Fasting Insulin: Often ordered with fasting glucose to calculate insulin resistance.
• Certain Metabolic and Hormonal Panels: Tests like cortisol, ACTH, or certain fertility hormones often require specific timing and fasting conditions.
• Triglycerides in High-Risk Patients: As mentioned above.
• Some Pre-Surgical Tests: To ensure baseline stability and reduce aspiration risk.

The Modern Paradigm: “Fasting is Not Routine”

The current best practice is individualized instructions. When you get a lab order, it should specify:

• “Fasting Required” (usually 8-12 hours, water only).
• “Non-Fasting” (come as you are).
• “Preferably Fasting” (ideal but not mandatory for interpretation).

Conclusion: Fasting blood tests didn’t go “out of fashion.” Instead, medical science progressed to show that for screening purposes in most healthy adults, non-fasting lipid and metabolic panels are sufficient and more practical. This shift reflects a move towards patient-centered care and evidence-based medicine. However, for specific diagnostic questions, fasting remains an essential and non-negotiable part of accurate testing. Always follow the specific instructions given by your healthcare provider or laboratory.