Why glucose-based results confirm her diagnosis
Type 2 diabetes is diagnosed when a fasting plasma glucose is 126 mg/dL (7.0 mmol/L) or higher on two separate days, when glycated hemoglobin (HbA1c) is 6.5% or higher, or by other glucose criteria. Her fasting values of 134 and 141 mg/dL on separate days meet the glucose criterion. Her 6.1% HbA1c would normally fall below the diagnostic cutoff, but in her case HbA1c is not reliable. When HbA1c is unreliable, glucose-based tests are used to diagnose and monitor diabetes.
Why thalassemia trait affects HbA1c
HbA1c measures the percentage of hemoglobin that has glucose attached. It depends on two assumptions: a normal red blood cell lifespan of about 120 days and normal hemoglobin structure. In beta-thalassemia trait and other hemoglobin variants, red cell turnover and hemoglobin composition can differ, and some laboratory methods are affected by abnormal hemoglobins. HbA1c may therefore read falsely low or high. Other conditions that make HbA1c unreliable include hemolysis, recent blood loss or transfusion, iron deficiency, pregnancy, and advanced kidney disease.
| Option | Accurate? | Reason |
|---|
| Thalassemia trait can make HbA1c unreliable | Yes | Altered red cells and hemoglobin affect the result |
| HbA1c shows only the past 2 weeks | No | Reflects about 2–3 months |
| HbA1c is not used for diagnosis | No | 6.5% or more is a diagnostic criterion |
| Obesity lowers HbA1c | No | Obesity does not alter the test |
Why the other explanations are wrong
HbA1c reflects average glucose over about 2–3 months, not 2 weeks. It is an accepted diagnostic test at 6.5% or more; the issue here is not the test in general but its reliability in her. Obesity raises diabetes risk but does not change how HbA1c is measured. Watch out! Note that the stem mentions her beta-thalassemia trait in the situation; details given in the setup often matter for later questions.
Exam takeaway
When a client has a hemoglobin disorder or a condition that changes red cell lifespan, the nurse relies on plasma glucose and self-monitoring results rather than HbA1c alone. Key point! Two fasting plasma glucose values of 126 mg/dL or more on separate days confirm diabetes, even if HbA1c is below 6.5%.