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Hemoglobin A1 C

Biological Variation:

CVw = within-subject biologic variation: 1,9%

CVg = between-subject biologic variation: 5.7%

Desirable specification

I = desirable specification for imprecision: 0,9%

B = desirable specification for inaccuracy: 1.5%

TE = desirable specification for allowable total error: 3,0%

Also:

“Many believe that performance goals for Hb A1c testing should be based on clinical requirements. There are 2 important questions for a physician to consider when using Hb A1c measurements to assess a patient's glycemic status. One is whether the patient's glycemic control is stable, improving, or deteriorating, and the other is how the Hb A1c result compares to the individual's target Hb A1c (the current ADA recommendation is 7% with the qualification that lower is better if feasible). In answer to the first question, many physicians have suggested that 0.5% Hb A1c is a “clinically significant change.” Importantly, treatment guidelines and algorithms from the ADA/EASD (26) and National Institute for Clinical Excellence in the UK (27) recommend evaluating new treatment regimens in terms of whether Hb A1c is lowered by 0.5 percentage points or more. Therefore it is important to be sure that a change of this magnitude is statistically significant and not due to analytical variation. Taking a statistically significant difference of 0.5% Hb A1c at an Hb A1c concentration of 7% as the goal for Hb A1c measurement, one can use the reference change value (RCV), also called critical difference, to calculate an appropriate goal in terms of a method's CV(28). For sequential results to be significantly different, the numbers must differ by more than the combined variation inherent in the 2 results: RCV (%) = 2(1/2) × 1.96 × [(CVA)2 + (CVI)2](1/2), where CVA is the analytical CV of the method (within-laboratory CV) and CVI is the within-subject biological variation. For Hb A1c the CVI is low,

At a given moment, there is no intraindividual variation. To hit the correct concentration depends on the validation status of the method and dependance on analytical deviation. The individual changes of HBA1c depend solely on actual glucose and hemoglobin concentrations. The rections leading to the glycated form of hemoglobin are pure chemical and evolve according to the law of mass action. When glucose concentration is lowered from 300 mg/100 ml to 120 mg/100 ml by insulin therapy, you observe a 1% decrease only after 1 week, or 3% after 1 month. So, intraindividual variation is very, very small.

What about the recent unit changes % to mmol/mol?

Conversions of the thresholds gives the following:

Clinically Sig change in HbA1c 0.5% = (- 18 mmol/mol)

CVw 1.9% = (- 2.7 mmol/mol)

the absolute values would be misleading ...

If I have a series of readings, mostly 3 months apart, I assume I could check whether changes in HbA1c readings were clinically significant (HbA1c change more than 0.5%) and also check if the change exceed the CVw to consider if it a 'valid' change and not due BV?

I’ve searched for guidelines re CVw;CVg appropriate for the age range of adolescents 15 to 24 year olds, but it looks like prev research only covered adult (> 18) and children (

I do not quite agree with the data given by Jasna Grieza, and derive the result using another approach, which is usually proposed by Clinical Chemists (Tietz, for example and general statisticians). You have the laboratory standard deviation of quality control for HbA1c CV=2% and your actual HbA1c-value of a patient of 6%. The question is: which value is significantly changed after insulin therapy. The formula is derived from a normal t-test for 2 results, i.e. the value of a previous test of 6% HbA1c and the actual value: The formula is: 2*square root of 2*CV: 2*1,41*2%=5,7%. Using the previous HbA1-test value of 6%, then 6*0,057=0,34. This means, that a significant decrease of HbA1c is obtained only with values below 5,7%. In case of a HbA1c-value of 10%, you need a decrease of 0,6 in order to reach significance of therapy (2*1,41*10%) It must be clear of course, that the significant difference depends on the actual values.

This is a general approach for therapy control taught to clinicians and in our student course of laboratory medicine for medical students in the University Medical School of Giessen, Germany and may be applied to all laboratory tests.

Sighart Golf

There is a paper published in 2010 by Desmeules et al. (Ann Clin Biochem 2010; 47: 35–38) about the biological variation of glycated haemoglobin in a paediatric population (age under 18). They calculated that the within-subject biological variation for HbA1c in this population was 4.8%. They also used the biological variation data to estimate the reference change value.

There is an excellent paper by several studies in Clinica Chimica Acta 411 (2010) 1606-1610 of Braga et al: biological variability of glycated hemoglobin. It shows that it is difficult to answer your question precisely because this variability seems different in the individual free from disease and diabetic patients