1. Overview
Fructosamine is a glycated serum protein formed by the non-enzymatic reaction between glucose and amino groups of circulating proteins, predominantly albumin. Chemically, it is a stable ketoamine (1-amino-1-deoxy fructose). Similar to hemoglobin A1c (HbA1c), fructosamine reflects glycemic control; however, it represents average blood glucose levels over a shorter period of approximately 2–3 weeks, corresponding to the half-life of serum proteins.
In diabetes mellitus, elevated blood glucose leads to increased protein glycation, contributing to long-term complications. Because fructosamine reflects recent glycemic status, it is particularly useful in situations where HbA1c may be unreliable.
2. Symptoms
Fructosamine itself does not cause symptoms. Clinical manifestations relate to the underlying glycemic status. Elevated fructosamine levels are associated with symptoms of hyperglycemia such as polyuria, polydipsia, fatigue, and poor wound healing, while low levels may reflect altered protein metabolism rather than glucose abnormalities.
Fructosamine testing is mainly a monitoring tool rather than a diagnostic marker for acute symptoms.
3. Causes
Increased fructosamine levels primarily result from persistent hyperglycemia, most commonly seen in diabetes mellitus. Other conditions associated with elevated fructosamine include multiple myeloma, monoclonal gammopathies, altered protein metabolism such as nephrotic syndrome, diminished protein synthesis in hepatic disease or liver cirrhosis, thyroid disorders, and malnutrition.
Decreased fructosamine levels may occur due to low serum albumin, protein loss, liver disease, or conditions affecting protein turnover. High intake of ascorbic acid (vitamin C) can interfere with the assay and falsely lower fructosamine values.
4. Risk Factors
Fructosamine testing is particularly valuable in patients where HbA1c interpretation is limited. Risk factors prompting its use include conditions with altered red blood cell lifespan, such as hemolytic anemia, sickle cell anemia, and other hemoglobinopathies.
It is also useful in gestational diabetes mellitus, pregnancy, and situations requiring short-term monitoring of glycemic control, such as recent changes in therapy or diet. Patients with chronic kidney disease or recent blood loss may benefit from fructosamine measurement since it is not affected by red blood cell turnover.
However, conditions affecting serum protein concentration, such as hypoalbuminemia or nephrotic syndrome, may influence fructosamine levels and should be considered during interpretation.
5. Prevention and Clinical Management
Fructosamine testing plays an important role in the short-term monitoring of diabetes management. Indications include assessment of recent response to antidiabetic therapy, monitoring gestational diabetes, evaluating glycemic control in patients with hemolytic anemia or hemoglobinopathies, pregnancy, and cases where HbA1c results are questionable.
Blood samples are collected in plain, EDTA, or heparinized tubes, with serum or plasma separated from red blood cells within 45 minutes of collection. After separation, samples remain stable for up to 72 hours at room temperature, two weeks when refrigerated, and up to two months when frozen. Patients should avoid ascorbic acid supplements for at least 24 hours before sample collection due to assay interference.
Several analytical methods are used to measure fructosamine, including affinity chromatography, high-performance liquid chromatography (HPLC), ion-exchange chromatography, quantitative spectrophotometry, capillary electrophoresis, radioimmunoassay, and ELISA.
The reference interval for non-diabetic individuals is approximately 205–285 mmol/L. Values between 286–340 mmol/L suggest mild hyperglycemia, 341–421 mmol/L indicate moderate hyperglycemia, and levels above 421 mmol/L reflect poorly controlled or advanced diabetes. Levels below 200 mmol/L may indicate hypoalbuminemia, liver disease, or protein loss.
Compared with HbA1c, it has a shorter half-life, allowing faster detection of changes in glycemic control. It is not affected by recent blood loss or chronic kidney disease and is particularly useful when rapid therapeutic adjustments are required. However, limitations include dependence on protein concentration and turnover, lower standardization compared with HbA1c, and reduced reliability in hypoalbuminemia.
Overall, it serves as a valuable adjunct to HbA1c, offering a reliable assessment of short-term glycemic control in specific clinical situations.
