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HbA1c and ketones

14 min

Skills you'll build2 skills
  • Recognize when red-cell changes make an HbA1c disagree with the glucose history
  • Choose a ketone test that detects beta-hydroxybutyrate in suspected DKA

Try first

Try first

A patient with hereditary spherocytosis and an active hemolytic anemia has diabetes. Home glucose readings average about 180 mg/dL. The HbA1c reads 5.4%, and the method shows no hemoglobin variant. What explains the gap?

Keep going to see the reasoning.

Right. Keep going to follow the reasoning.

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Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

HbA1c and red-cell survival

Hemoglobin A1c (HbA1c) forms when glucose attaches, without an enzyme, to the N-terminal valine of the hemoglobin A beta chain. It reflects glycemia over roughly the previous 2 to 3 months, with recent weeks weighted more.1 The result also depends on how long the red cells have circulated:2

  • Hemolysis, recovery from blood loss and erythropoietin use leave a younger red-cell population. HbA1c then reads lower than the glucose history predicts.
  • Iron deficiency may raise HbA1c.
  • Hemoglobin variants can interfere, in a direction that depends on the method.

When hemoglobin A is absent, as in HbSS, HbCC and HbSC, HbA1c cannot be measured and is not reported. Fructosamine and glycated albumin reflect about the previous 15 to 30 days and do not depend on red cells.1

The estimated average glucose (eAG) converts an HbA1c into glucose units, so it can be compared with measured glucose:3

eAG (mg/dL) = 28.7 × HbA1c (%) − 46.7

A large gap between the eAG and the glucose history is investigated by reviewing the blood count, the transfusion history and the analyzer's variant pattern.2

Measure the ketone that predominates

The liver makes three ketone bodies when fatty-acid oxidation increases. Beta-hydroxybutyrate is the main ketoacid in diabetic ketoacidosis (DKA).1

Ketone bodyShare in DKANitroprusside reactionEnzymatic blood method
Beta-hydroxybutyratePredominantNoneMeasured with beta-hydroxybutyrate dehydrogenase
AcetoacetateSmallerPurple colorNot measured
AcetoneMinorWeak, with glycine formulationsNot measured

Blood beta-hydroxybutyrate is the preferred test for diagnosing DKA and following it. The consensus criterion is beta-hydroxybutyrate of 3.0 mmol/L or higher.4 A urine nitroprusside result can underestimate ketosis early in DKA. During treatment, beta-hydroxybutyrate converts to acetoacetate, so the urine result can rise while the patient recovers.4

Follow the bench demonstration

Sources for this step
References
  1. Sacks DB, Arnold M, Bakris GL, et al. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Diabetes Care. 2023;46(10):e151-e199. doi:10.2337/dci23-0036
  2. National Glycohemoglobin Standardization Program. Factors that interfere with HbA1c test results. Updated June 23, 2026. Accessed September 27, 2026. https://ngsp.org/factors.asp
  3. National Glycohemoglobin Standardization Program. HbA1c and estimated average glucose. Accessed September 27, 2026. https://ngsp.org/A1ceAG.asp
  4. Umpierrez GE, Davis GM, ElSayed NA, et al. Hyperglycemic crises in adults with diabetes: a consensus report. Diabetes Care. 2024;47(8):1257-1275. doi:10.2337/dci24-0032

Watch one

Read each decision and its explanation.

An adult with type 2 diabetes has an HbA1c that the clinic questions. Six fasting plasma glucose results over the past 3 months ranged from 150 to 190 mg/dL, averaging 170 mg/dL. The Meniscus CX-800 measures HbA1c by ion-exchange chromatography, and the chromatogram shows no variant peak.

Does the HbA1c reflect this patient's glucose history?

TestResultReference intervalFlag
HbA1c5.6 %4.0–5.6 %4.0–5.6
Hemoglobin9.8 g/dL Low12.0–15.5 g/dL12.0–15.5Low
Reticulocytes6.5 % High0.5–2.5 %0.5–2.5High
Lactate dehydrogenase410 U/L High120–246 U/L120–246High
Haptoglobin<10 mg/dL Low30–200 mg/dL30–200Low

Specimen: H 10, L 15, I 2. EDTA whole blood for HbA1c and the blood count; serum for LDH and haptoglobin

  1. Convert the HbA1c: eAG = 28.7 × 5.6 − 46.7 = 114 mg/dL. The measured glucose results average 170 mg/dL.

    The eAG converts the HbA1c into glucose units, so the two can be compared directly.

  2. Check the chromatogram: no variant peak, so an analytic interference from a variant is unlikely.

    A variant can shift the result in a direction that depends on the method, so check the analyzer's chromatogram next.

  3. Check the blood count. A hemoglobin of 9.8 g/dL with reticulocytes at 6.5% shows many young cells.

    HbA1c builds up over each red cell's life, so a young red-cell population has less of it.

  4. Read the hemolysis markers: a high lactate dehydrogenase and a haptoglobin below 10 mg/dL point to shortened red-cell survival from hemolysis.

    These results show why the cells are young.

  5. Report the HbA1c with your procedure's comment on shortened red-cell survival, naming glucose results or fructosamine as the better measure.

    The assay measured the cells in the tube correctly, and the report needs to explain why the value is low.

The HbA1c of 5.6% (eAG 114 mg/dL) reads low for a glucose history averaging 170 mg/dL, because hemolysis has shortened red-cell survival.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

How does shortened erythrocyte survival usually affect HbA1c relative to the same glycemic exposure?

Incorrect. Younger cells have had less time in circulation, so they are less glycated.

Incorrect. A technically accurate assay still measures a cell population whose exposure time has changed.

Correct. Hemolysis, recent blood loss, and erythropoietin use leave a younger red-cell population, so HbA1c reads lower than the glucose history predicts.

Hint
  1. Glucose attaches to hemoglobin steadily through each red cell's life.
  2. Ask how long the cells in the specimen have been circulating when survival is short.

Review HbA1c and other glycated proteins

Problem 2 of 3 · Hints available

Which measurement directly assesses the predominant ketoacid in diabetic ketoacidosis (DKA)?

Correct. Beta-hydroxybutyrate predominates in DKA, and enzymatic methods using beta-hydroxybutyrate dehydrogenase quantify it in blood.

Incorrect. Nitroprusside reacts with acetoacetate and, in glycine formulations, weakly with acetone. Beta-hydroxybutyrate gives no reaction.

Incorrect. The anion gap reflects unmeasured anions indirectly and gives no beta-hydroxybutyrate concentration. Mixed acid-base disorders and hyperchloremic acidosis also limit it.

Hint
  1. Start with the ketone body that predominates in DKA.
  2. Ask which ketone bodies the nitroprusside reaction detects.

Review Ketones and hyperglycemic crises

Problem 3 of 3 · On your own

A patient treated for DKA is followed with two tests. At admission, blood beta-hydroxybutyrate is 6.2 mmol/L and urine nitroprusside ketones are 1+. Eight hours into treatment, beta-hydroxybutyrate is 1.4 mmol/L and urine ketones are 3+. Which result shows the course of the ketoacidosis?

Nitroprusside detects acetoacetate and does not detect beta-hydroxybutyrate. As beta-hydroxybutyrate converts to acetoacetate during recovery, the urine result rises.

Read urine nitroprusside as total ketones in DKA

Nitroprusside reacts with acetoacetate and weakly with acetone. It does not react with beta-hydroxybutyrate, the main ketoacid in diabetic ketoacidosis (DKA). Early urine results can be low and then rise during recovery as beta-hydroxybutyrate converts to acetoacetate. The urine test can therefore misstate both severity and trend.

The two tests measure different ketone bodies. During recovery they are expected to move apart.

Blood beta-hydroxybutyrate measures the main ketoacid directly, and it fell from 6.2 to 1.4 mmol/L. The urine rise comes from beta-hydroxybutyrate converting to acetoacetate.

Review Ketones and hyperglycemic crises

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • A 34-year-old woman with sickle cell disease and type 2 diabetes, MRN 5820394, has an HbA1c ordered at a clinic visit.
  • The Meniscus CX-800 measures HbA1c by ion-exchange chromatography.
  • The chromatogram shows Hb S about 88%, Hb F 9% and Hb A2 3%, with no Hb A peak.
  • The analyzer gives no HbA1c value and flags a variant.
  • The clinic calls and asks the laboratory to run the HbA1c on another method.
Decision 1 of 3

Why can this specimen not give an HbA1c that reflects the patient's glycemia?

HbA1c is glycated hemoglobin A. This specimen has no hemoglobin A, so no method can find it.

Hb F can interfere in some methods. Here the Hb A peak is missing.

HbA1c is formed on hemoglobin A, which this specimen lacks. Sickled cells also circulate for a short time, so glycation on any hemoglobin would understate the glucose history.

Review HbA1c and other glycated proteins

Decision 2 of 3

What do you report?

The comment tells the clinic why no value appears and which other tests can be used.

Any value from these cells would read low for the glucose history, because the cells circulate for a short time. A number would make glucose control look better than it is.

Read a low HbA1c as good control despite hemolysis

Hemolysis, recent blood loss, and erythropoietin use lower the average age of circulating red cells, so HbA1c reads lower than the glucose history predicts. Iron deficiency may raise it. Accepting the low value makes glucose control look better than it is and misses the red-cell cause of the discrepancy.

A new specimen has the same hemoglobin pattern and gives the same result.

No HbA1c peak exists to estimate from, and an estimated value would be reported as a measured result.

Review HbA1c and other glycated proteins

Decision 3 of 3

The clinic asks which test can follow her glucose control. Which marker does not depend on red cells?

The eAG comes from an HbA1c, so it has the same red-cell limitation.

Fructosamine measures glycated serum protein over about the previous 15 to 30 days. Protein loss and albumin turnover still affect it.

Transfusion mixes donor cells into the specimen and changes the relationship between HbA1c and glycemia.

Review HbA1c and other glycated proteins

The chromatogram showed no Hb A peak. HbA1c is formed on hemoglobin A, so a specimen without it has no HbA1c to report, and the comment names the tests that can be used.

For reference

Sources checked