A client is scheduled for a fasting blood glucose test in the morning. Which instruction should the nurse give?

FASTING BLOOD GLUCOSE test measures blood glucose after an adequate fasting period and is used to: SCREEN for diabetes (fasting glucose ≥126 mg/dL on two separate occasions = diabetes); DIAGNOSE impaired fasting glucose (prediabetes: 100-125 mg/dL); MONITOR glycemic control in known diabetics (less commonly than A1c now, but still used).

Fasting requirements: nothing to eat or drink (except WATER) for 8-12 hours before the test; water is allowed and encouraged (does not affect glucose; prevents dehydration which can concentrate the sample); no food, juice, coffee, milk, or caloric beverages; smoking may affect results (advise against).

Medication considerations: most oral medications can be taken with a small sip of water unless specifically contraindicated; insulin-dependent diabetics should hold morning insulin dose UNLESS fasting glucose is known (hypoglycemia risk); specific instructions from the provider take precedence.

Common lab tests and their requirements: FASTING (nothing except water, 8-12 hours): blood glucose, HbA1c (no special requirements actually, but many labs draw it fasting), lipid panel, iron studies.

No special prep: CBC, electrolytes, BMP, CMP (though many labs prefer early morning).

Timed samples: cortisol (AM/PM), ACTH, morning cortisol best drawn 8 AM.

Pn role: provide clear verbal AND written instructions; confirm the client understood (teach-back); document that instructions were given; confirm appointment time and location; advise the client to bring their glucose monitor if diabetic; if the client accidentally ate, inform the lab and the ordering provider before drawing — the fasting interpretation cannot be applied.