Does fructosamine testing require fasting?

Fructosamine Testing Does Not Require Fasting

Fructosamine testing does not require fasting prior to blood collection. Unlike some other glycemic tests such as fasting plasma glucose (FPG), fructosamine measurements can be performed regardless of when the patient last ate.

What is Fructosamine?

Fructosamine is a glycated serum protein that reflects average blood glucose levels over the preceding 2-3 weeks 1. This shorter timeframe contrasts with HbA1c, which provides an index of glycemic status over a longer period of 2-3 months 1.

• Primarily measures glycation of serum albumin (half-life of 14-20 days)
• Reflects shorter-term glycemic control compared to HbA1c
• Also referred to as glycated serum protein (GSP) or glycated serum albumin (GSA)

Clinical Utility of Fructosamine

Fructosamine testing has several specific clinical applications:

• When HbA1c may be unreliable due to:

  • Hemolytic anemias
  • Hemoglobinopathies
  • Conditions with increased red blood cell turnover 1
  • Pregnancy (second and third trimesters)
  • Recent blood loss or transfusion
  • Erythropoietin therapy

• For monitoring short-term changes in glycemic control:

  • After major changes in therapy
  • In diabetic pregnancy 1
  • When rapid assessment of glycemic control is needed 2

Advantages and Limitations

Advantages:

• No fasting required (unlike FPG which requires 8 hours of fasting) 1
• Reflects more recent glycemic control than HbA1c
• Can be performed more rapidly in some laboratories 2
• Relatively inexpensive and simple to perform 3

Limitations:

• Values may vary with changes in protein synthesis or clearance 1
• Can be affected by acute systemic illness or liver disease
• Debate exists about whether results should be corrected for serum protein or albumin concentrations 1
• Moderate sensitivity (67.3%) but high specificity (97.3%) as a diagnostic test for diabetes 4
• Has not been shown to correlate with risk of developing chronic complications of diabetes, unlike HbA1c 1

Correlation with Other Glycemic Measures

Fructosamine measurements correlate with both HbA1c and fasting blood glucose:

• Correlation with HbA1c: r = 0.41, p < 0.01 3
• Correlation with fasting blood glucose: r = 0.45, p < 0.01 3

A recent study demonstrated a linear correlation between fructosamine level and mean blood glucose level, with the equation: Mean glucose level = (0.5157 × Fructosamine) - 20 5.

Clinical Recommendations

1. Fructosamine testing can be performed at any time of day without fasting requirements.

2. Consider fructosamine testing as an alternative to HbA1c when:

   • HbA1c results may be unreliable due to conditions affecting red blood cell lifespan
   • Short-term glycemic changes need to be assessed
   • Same-day results are needed for clinical decision-making

3. For routine monitoring of diabetes, HbA1c remains the preferred test due to:

   • Established relationship with diabetes complications
   • Standardized methodology
   • Broader evidence base supporting its use

4. Fructosamine should not be considered equivalent to HbA1c, as it only indicates glycemic control over a shorter period 1.

Important Caveats

• Fructosamine would need to be performed monthly to gather similar information as quarterly HbA1c tests 1.
• The reliability of fructosamine assays can be variable, which may limit clinical utility 1.
• Despite the convenience of no fasting requirement, fructosamine has not been widely adopted as a screening test for diabetes due to considerable overlap between diabetic and non-diabetic values 4.