A 13-year-old boy in Al Ain has had thirst and polyuria for 3 weeks. He weighs 92 kg (BMI 33 kg/m², above the 99th percentile for age) and has dark, velvety skin on the back of his neck. His mother developed type 2 diabetes at 41; his father does not have diabetes. At presentation: random plasma glucose 16.4 mmol/L (295 mg/dL); HbA1c 9.2% (77 mmol/mol); venous pH 7.37 (reference 7.32-7.43); bicarbonate 23 mmol/L; beta-hydroxybutyrate 0.4 mmol/L (reference below 0.6). Next morning: fasting glucose 9.8 mmol/L (177 mg/dL) and C-peptide 1.6 nmol/L (4.8 ng/mL) (fasting reference 0.3-1.0 nmol/L). GAD65, IA-2 and ZnT8 antibodies are all negative. The best-supported classification is:

Maturity-onset diabetes of the young

A 31-year-old woman at 26 weeks of pregnancy attends an antenatal clinic in Abu Dhabi that screens for gestational diabetes (GDM) by the two-step approach. Her 50 g non-fasting screen gave a 1-hour glucose of 9.1 mmol/L (164 mg/dL), above the clinic's 7.8 mmol/L (140 mg/dL) cut-off, so a 100 g, 3-hour OGTT was done after an overnight fast. Results: fasting 5.1 mmol/L (92 mg/dL), 1 hour 10.4 mmol/L (187 mg/dL), 2 hours 8.4 mmol/L (151 mg/dL), 3 hours 6.6 mmol/L (119 mg/dL). The clinic uses the Carpenter-Coustan thresholds of 5.3, 10.0, 8.6 and 7.8 mmol/L (95, 180, 155 and 140 mg/dL) and diagnoses GDM only when two or more values meet or exceed them. The correct report is:

GDM not confirmed: only one value meets its threshold

GDM: the raised 50 g screen confirms the diagnosis

GDM: the fasting and 1-hour values both qualify

GDM: one raised value on the 100 g test is enough

A 63-year-old man with type 2 diabetes on unchanged doses of metformin and basal insulin had HbA1c results of 8.4% and 8.6% (68 and 70 mmol/mol) over the past year, all by the same cation-exchange HPLC method with normal chromatograms. Five weeks ago he had a bleeding duodenal ulcer and received 4 units of red cells. Today: HbA1c 6.3% (45 mmol/mol) with a normal chromatogram; hemoglobin 108 g/L (10.8 g/dL) (reference 130-170 g/L); reticulocytes 3.8% (reference 0.5-2.5%); ferritin 18 µg/L (reference 30-400 µg/L). His downloaded glucose meter readings average 10.2 mmol/L (184 mg/dL), the same as before the bleed. What best explains the fall in his HbA1c?

Transfused and newly made red cells lowering HbA1c

A hemoglobin variant appearing after transfusion

Iron deficiency after the bleed falsely lowering HbA1c

A true improvement in his average glucose

Boronate affinity HbA1c methods are little affected by most hemoglobin variants because they:

Bind the cis-diol groups of the attached glucose

Separate hemoglobins by their electrical charge

Measure glucose released from hemoglobin by enzymes

Use antibodies to the glycated beta-chain end

A non-obese 34-year-old man was diagnosed with type 2 diabetes a year ago. Despite two oral agents, his HbA1c has risen from 7.2% to 9.6% (55 to 81 mmol/mol). Fasting C-peptide is low and GAD65 antibodies are strongly positive. Which diagnosis fits best?

Slowly progressive autoimmune diabetes (LADA)

Maturity-onset diabetes of the young (MODY)

Diabetes from excess growth hormone

Type 2 diabetes with simple beta-cell exhaustion

Diabetes mellitus: diagnosis and monitoring

28 DOH Abu Dhabi (HAAD) lab licensing practice questions on Diabetes mellitus: diagnosis and monitoring, part of Clinical Chemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 13-year-old boy in Al Ain has had thirst and polyuria for 3 weeks. He weighs 92 kg (BMI 33 kg/m², above the 99th percentile for age) and has dark, velvety skin on the back of his neck. His mother developed type 2 diabetes at 41; his father does not have diabetes. At presentation: random plasma glucose 16.4 mmol/L (295 mg/dL); HbA1c 9.2% (77 mmol/mol); venous pH 7.37 (reference 7.32-7.43); bicarbonate 23 mmol/L; beta-hydroxybutyrate 0.4 mmol/L (reference below 0.6). Next morning: fasting glucose 9.8 mmol/L (177 mg/dL) and C-peptide 1.6 nmol/L (4.8 ng/mL) (fasting reference 0.3-1.0 nmol/L). GAD65, IA-2 and ZnT8 antibodies are all negative. The best-supported classification is:
1. AMaturity-onset diabetes of the young
2. BAutoimmune type 1 diabetes
3. CIdiopathic (type 1B) diabetes
4. DType 2 diabetes
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Answer: D · Type 2 diabetes
The boy has severe obesity and acanthosis nigricans, both signs of insulin resistance, and a parent with type 2 diabetes. His fasting C-peptide is raised despite hyperglycemia, so insulin secretion is preserved, and he has no ketosis or acidosis. Negative GAD65, IA-2 and ZnT8 antibodies make autoimmune type 1 diabetes unlikely, and type 1B diabetes means insulin deficiency without autoimmunity, which the high C-peptide rules out. MODY is suspected in antibody-negative young people without obesity or insulin resistance who have diabetes in several generations, which does not fit here. Youth-onset type 2 diabetes is rising with childhood obesity, and the ADA still advises islet antibody testing in obese children, because some of them have type 1 diabetes.
- A: MODY is suspected in non-obese, antibody-negative patients with diabetes across generations, not with marked insulin resistance.
- B: All three islet antibodies are negative and C-peptide is high, so autoimmune insulin deficiency is unlikely.
- C: Type 1B diabetes means insulin deficiency without autoimmunity, but his C-peptide is raised.
Question 2 · Hard
A 31-year-old woman at 26 weeks of pregnancy attends an antenatal clinic in Abu Dhabi that screens for gestational diabetes (GDM) by the two-step approach. Her 50 g non-fasting screen gave a 1-hour glucose of 9.1 mmol/L (164 mg/dL), above the clinic's 7.8 mmol/L (140 mg/dL) cut-off, so a 100 g, 3-hour OGTT was done after an overnight fast. Results: fasting 5.1 mmol/L (92 mg/dL), 1 hour 10.4 mmol/L (187 mg/dL), 2 hours 8.4 mmol/L (151 mg/dL), 3 hours 6.6 mmol/L (119 mg/dL). The clinic uses the Carpenter-Coustan thresholds of 5.3, 10.0, 8.6 and 7.8 mmol/L (95, 180, 155 and 140 mg/dL) and diagnoses GDM only when two or more values meet or exceed them. The correct report is:
1. AGDM: the raised 50 g screen confirms the diagnosis
2. BGDM: the fasting and 1-hour values both qualify
3. CGDM not confirmed: only one value meets its threshold
4. DGDM: one raised value on the 100 g test is enough
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Answer: C · GDM not confirmed: only one value meets its threshold
Against the stated thresholds, the fasting value (5.1 against 5.3 mmol/L), the 2-hour value (8.4 against 8.6 mmol/L) and the 3-hour value (6.6 against 7.8 mmol/L) are all below their cut-offs; only the 1-hour value of 10.4 mmol/L exceeds 10.0 mmol/L. With one abnormal value, this two-step protocol's criteria are not met. A single raised value is diagnostic only in the one-step 75 g OGTT (IADPSG criteria), whose lower fasting cut-off of 5.1 mmol/L (92 mg/dL) can make her fasting value look abnormal to someone applying the wrong criteria. The 50 g challenge is only a screen that selects women for the diagnostic test. The laboratory reports each value against the protocol's thresholds, and any follow-up is the clinician's decision.
- A: The 50 g test only screens; the diagnosis rests on the 100 g OGTT.
- B: Her fasting 5.1 mmol/L is below the 5.3 mmol/L Carpenter-Coustan cut-off; 5.1 is the one-step 75 g threshold.
- D: This protocol needs two or more values at or above threshold; one is not enough.
Question 3 · Hard
A 63-year-old man with type 2 diabetes on unchanged doses of metformin and basal insulin had HbA1c results of 8.4% and 8.6% (68 and 70 mmol/mol) over the past year, all by the same cation-exchange HPLC method with normal chromatograms. Five weeks ago he had a bleeding duodenal ulcer and received 4 units of red cells. Today: HbA1c 6.3% (45 mmol/mol) with a normal chromatogram; hemoglobin 108 g/L (10.8 g/dL) (reference 130-170 g/L); reticulocytes 3.8% (reference 0.5-2.5%); ferritin 18 µg/L (reference 30-400 µg/L). His downloaded glucose meter readings average 10.2 mmol/L (184 mg/dL), the same as before the bleed. What best explains the fall in his HbA1c?
1. AA hemoglobin variant appearing after transfusion
2. BTransfused and newly made red cells lowering HbA1c
3. CIron deficiency after the bleed falsely lowering HbA1c
4. DA true improvement in his average glucose
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Answer: B · Transfused and newly made red cells lowering HbA1c
HbA1c depends on both the glucose level and how long red cells have been exposed to it. Many of his circulating red cells are now donor cells that spent their life at normal glucose, and the raised reticulocyte count shows a wave of young cells with little time to glycate; both lower HbA1c for about 2-3 months. His meter average of 10.2 mmol/L corresponds to an HbA1c of about 8% by the ADAG equation, so his control has not changed. Iron deficiency, shown by the low ferritin, tends to raise HbA1c and cannot explain a fall, and the normal chromatogram excludes a variant. Until the transfused cells are replaced, meter data, continuous glucose monitoring or fructosamine should guide treatment.
- A: The chromatogram is normal, so no variant is present.
- C: Iron deficiency tends to raise HbA1c, not lower it.
- D: His meter average is unchanged and matches an HbA1c of about 8%.
Question 4 · Medium
Boronate affinity HbA1c methods are little affected by most hemoglobin variants because they:
1. ASeparate hemoglobins by their electrical charge
2. BMeasure glucose released from hemoglobin by enzymes
3. CBind the cis-diol groups of the attached glucose
4. DUse antibodies to the glycated beta-chain end
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Answer: C · Bind the cis-diol groups of the attached glucose
Boronate binds the cis-diol groups of glucose attached to hemoglobin, whatever the globin's charge or sequence. It measures total glycated hemoglobin and is calibrated to report NGSP-equivalent HbA1c values. This makes it a useful check when a variant interferes with other methods. It cannot correct for shortened red cell survival, as in sickle cell disease, because that problem is biological, not analytical.
- A: Charge separation describes ion-exchange HPLC, which variants can disturb.
- B: Enzymatic methods cleave a glycated N-terminal peptide; they do not release glucose.
- D: Immunoassays target the beta-chain N-terminus, where variants such as HbS and HbC lie.
Question 5 · Hard
A non-obese 34-year-old man was diagnosed with type 2 diabetes a year ago. Despite two oral agents, his HbA1c has risen from 7.2% to 9.6% (55 to 81 mmol/mol). Fasting C-peptide is low and GAD65 antibodies are strongly positive. Which diagnosis fits best?
1. ASlowly progressive autoimmune diabetes (LADA)
2. BMaturity-onset diabetes of the young (MODY)
3. CDiabetes from excess growth hormone
4. DType 2 diabetes with simple beta-cell exhaustion
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Answer: A · Slowly progressive autoimmune diabetes (LADA)
Positive islet autoantibodies, most often GAD65 in adults, together with a falling C-peptide show autoimmune destruction of the beta cells. The ADA classes this slowly progressive adult form, often called LADA, within type 1 diabetes. These patients are often misclassified as type 2 at first and usually need insulin early. Testing antibodies and C-peptide in lean adults who fail oral agents prevents long delays in treatment.
- B: MODY is antibody-negative, with preserved C-peptide and a strong family history.
- C: Excess growth hormone causes insulin resistance with high insulin, not autoimmunity.
- D: Type 2 diabetes is antibody-negative, with normal or high C-peptide early on.
Question 6 · Easy
By ADA criteria, which HbA1c range indicates prediabetes?
1. A5.7-6.4% (39-47 mmol/mol)
2. B5.0-5.6% (31-38 mmol/mol)
3. C6.0-6.4% (42-47 mmol/mol)
4. D6.5-7.0% (48-53 mmol/mol)
Answer and explanation in LearnFree account
Question 7 · Medium
During a 75 g oral glucose tolerance test, a patient vomits 20 minutes after drinking the glucose. What should the laboratory do?
1. AGive half a dose more and continue the timing
2. BStop the test and rebook it for another day
3. CContinue and report the 2-hour result as usual
4. DGive a second 75 g load and restart the timing
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Question 8 · Easy
At a workplace screening day in Abu Dhabi, staff cannot be asked to fast. Which ADA-recommended screening test for diabetes can be used?
1. AHbA1c
2. B75 g oral glucose tolerance test
3. CUrine glucose by reagent strip
4. DFasting plasma glucose
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Question 9 · Hard
A 29-year-old woman at a UAE premarital screening clinic also has an HbA1c ordered. On cation-exchange HPLC, an unknown peak makes up 38% of total hemoglobin and the HbA1c is flagged. Her CBC is normal. What is the best action?
1. AReport the HbA1c as printed, without any comment
2. BRecalibrate the HPLC and repeat the same sample
3. CEstimate her HbA1c from a fasting glucose instead
4. DWithhold HbA1c; retest by boronate affinity and identify the variant
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Question 10 · Hard
An asymptomatic 46-year-old has one fasting blood sample: plasma glucose 7.3 mmol/L (131 mg/dL) and HbA1c 6.7% (50 mmol/mol). ADA cut-offs: fasting glucose 7.0 mmol/L (126 mg/dL); HbA1c 6.5% (48 mmol/mol). The correct interpretation is:
1. APrediabetes, to be retested within a year
2. BDiabetes is confirmed without a repeat sample
3. CDiabetes is likely, but a second sample is needed
4. DAn OGTT is needed before any diagnosis
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Question 11 · Medium
An HbA1c of 53 mmol/mol (IFCC units) corresponds to about which NGSP/DCCT value?
1. A6.5%
2. B8.0%
3. C7.0%
4. D5.3%
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Question 12 · Medium
On a cation-exchange HPLC HbA1c analyzer, an unexpected extra peak on the chromatogram most often indicates:
1. AA clotted sample with a low hemoglobin
2. BRecent transfusion with donor red cells
3. CPoor control of diabetes over 3 months
4. DA hemoglobin variant such as HbS or HbD
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Question 13 · Medium
After a big change in treatment, HbA1c changes noticeably within about a month, even though red cells live about 120 days. Why?
1. AGlucose of the last 30 days gives about half of HbA1c
2. BGlycation is reversed quickly once glucose falls
3. CHbA1c reflects only the last 2 to 3 weeks
4. DOld red cells are removed faster when glucose falls
Answer and explanation in LearnFree account
Question 14 · Easy
HbA1c is hemoglobin A with glucose attached, without enzymes, to:
1. AThe N-terminal valine of each alpha chain
2. BThe C-terminal histidine of each beta chain
3. CThe N-terminal valine of each beta chain
4. DThe iron atom at the center of the heme
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Question 15 · Hard
A patient's HbA1c is 8.0% (64 mmol/mol). Using the ADAG equation, eAG (mmol/L) = 1.59 x HbA1c (%) - 2.59, what is the estimated average glucose?
1. A8.0 mmol/L (144 mg/dL)
2. B10.1 mmol/L (183 mg/dL)
3. C15.3 mmol/L (276 mg/dL)
4. D12.7 mmol/L (229 mg/dL)
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Question 16 · Easy
For a standard oral glucose tolerance test in a non-pregnant adult, the glucose load is:
1. A1 g of glucose per kg body weight
2. B50 g of glucose, without fasting
3. C75 g of anhydrous glucose in water
4. D100 g of glucose in water
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Question 17 · Medium
In the ADA two-step approach to screening for gestational diabetes, the first step is:
1. AAn HbA1c, with 5.7% or more taken as positive
2. BA 100 g fasting load with glucose over 3 hours
3. CA 50 g non-fasting load with a 1-hour glucose
4. DA 75 g fasting load with glucose at 0, 1 and 2 hours
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Question 18 · Hard
A slim 26-year-old woman has a fasting glucose of 6.6 mmol/L (119 mg/dL) at a pre-employment check. Her mother and grandfather have mild diabetes that never needed treatment. HbA1c 6.3% (45 mmol/mol); islet antibodies negative; C-peptide normal; 75 g OGTT: fasting 6.5 mmol/L (117 mg/dL), 2 hours 7.6 mmol/L (137 mg/dL). The most likely cause is:
1. AHNF1A MODY
2. BType 2 diabetes
3. CEarly autoimmune type 1 diabetes
4. DGlucokinase (GCK) MODY
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Question 19 · Hard
A 60-year-old man on hemodialysis receives erythropoietin. His HbA1c is 6.1% (43 mmol/mol), but continuous glucose monitoring shows an average glucose of about 10 mmol/L (180 mg/dL). The best explanation is:
1. AErythropoietin-driven young red cells lower HbA1c
2. BIron deficiency in dialysis falsely lowers HbA1c
3. CCarbamylated hemoglobin from uremia raises HbA1c
4. DHeparin from dialysis interferes with the method
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Question 20 · Medium
Three weeks after starting insulin, a doctor wants a laboratory test that shows how average glucose has changed since treatment began. Which test best reflects this period?
1. AFructosamine
2. BFasting plasma glucose
3. CHbA1c
4. DUrine albumin-to-creatinine ratio
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Question 21 · Hard
An asymptomatic adult has fasting plasma glucose 7.4 mmol/L (133 mg/dL) and HbA1c 6.0% (42 mmol/mol) on the same sample. Hemoglobin and red cell indices are normal. By ADA guidance (fasting glucose 7.0 mmol/L [126 mg/dL]; HbA1c 6.5% [48 mmol/mol]), what is the next step?
1. ADiagnose diabetes on the fasting glucose alone
2. BExclude diabetes, since HbA1c is below 6.5%
3. CRepeat the fasting plasma glucose on a new sample
4. DRepeat the HbA1c by a different method first
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Question 22 · Hard
A 55-year-old man with type 2 diabetes has three urine albumin-to-creatinine ratio (ACR) results over 5 months: 4.6, 2.2 and 5.1 mg/mmol (41, 19 and 45 mg/g). Below 3 mg/mmol (30 mg/g) is normal; 3-30 mg/mmol (30-300 mg/g) is moderately increased. None followed exercise or infection. How should they be interpreted?
1. ATransient albuminuria needing no follow-up
2. BNormal, because one of the three is normal
3. CPersistent moderately increased albuminuria
4. DSeverely increased albuminuria (A3)
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Question 23 · Medium
A 75 g OGTT at 26 weeks of pregnancy is shown, with the IADPSG one-step thresholds marked at each time. How should the result be interpreted?
Figure: MedExams
1. AGestational diabetes mellitus
2. BNormal, as only one value is raised
3. CBorderline; repeat in 2 weeks
4. DOvert diabetes in pregnancy
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Question 24 · Hard
A 52-year-old man has a 75 g OGTT. His results, the tube used for each sample and the WHO 2-hour cut-offs are shown. In unseparated blood at room temperature, glucose falls by about 5-7% per hour. What should the laboratory do with the 2-hour result?
Figure: MedExams
1. AReject it and repeat the test
2. BAdd 20% to it and report it
3. CReport normal glucose tolerance
4. DReport impaired glucose tolerance
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Question 25 · Easy
Refer to the 75 g oral glucose tolerance test shown, with the WHO cut-offs for the 2-hour value drawn. The fasting cut-off for diabetes is 7.0 mmol/L (126 mg/dL). The result is classified as:
Figure: MedExams
1. ADiabetes mellitus
2. BImpaired fasting glucose
3. CImpaired glucose tolerance
4. DNormal glucose tolerance
Answer and explanation in LearnFree account

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Diabetes mellitus: diagnosis and monitoring

Boronate affinity HbA1c methods are little affected by most hemoglobin variants because they:

A non-obese 34-year-old man was diagnosed with type 2 diabetes a year ago. Despite two oral agents, his HbA1c has risen from 7.2% to 9.6% (55 to 81 mmol/mol). Fasting C-peptide is low and GAD65 antibodies are strongly positive. Which diagnosis fits best?

By ADA criteria, which HbA1c range indicates prediabetes?

During a 75 g oral glucose tolerance test, a patient vomits 20 minutes after drinking the glucose. What should the laboratory do?

At a workplace screening day in Abu Dhabi, staff cannot be asked to fast. Which ADA-recommended screening test for diabetes can be used?

A 29-year-old woman at a UAE premarital screening clinic also has an HbA1c ordered. On cation-exchange HPLC, an unknown peak makes up 38% of total hemoglobin and the HbA1c is flagged. Her CBC is normal. What is the best action?

An asymptomatic 46-year-old has one fasting blood sample: plasma glucose 7.3 mmol/L (131 mg/dL) and HbA1c 6.7% (50 mmol/mol). ADA cut-offs: fasting glucose 7.0 mmol/L (126 mg/dL); HbA1c 6.5% (48 mmol/mol). The correct interpretation is:

An HbA1c of 53 mmol/mol (IFCC units) corresponds to about which NGSP/DCCT value?

On a cation-exchange HPLC HbA1c analyzer, an unexpected extra peak on the chromatogram most often indicates:

After a big change in treatment, HbA1c changes noticeably within about a month, even though red cells live about 120 days. Why?

HbA1c is hemoglobin A with glucose attached, without enzymes, to:

A patient's HbA1c is 8.0% (64 mmol/mol). Using the ADAG equation, eAG (mmol/L) = 1.59 x HbA1c (%) - 2.59, what is the estimated average glucose?

For a standard oral glucose tolerance test in a non-pregnant adult, the glucose load is:

In the ADA two-step approach to screening for gestational diabetes, the first step is:

A 60-year-old man on hemodialysis receives erythropoietin. His HbA1c is 6.1% (43 mmol/mol), but continuous glucose monitoring shows an average glucose of about 10 mmol/L (180 mg/dL). The best explanation is:

Three weeks after starting insulin, a doctor wants a laboratory test that shows how average glucose has changed since treatment began. Which test best reflects this period?

An asymptomatic adult has fasting plasma glucose 7.4 mmol/L (133 mg/dL) and HbA1c 6.0% (42 mmol/mol) on the same sample. Hemoglobin and red cell indices are normal. By ADA guidance (fasting glucose 7.0 mmol/L [126 mg/dL]; HbA1c 6.5% [48 mmol/mol]), what is the next step?

A 75 g OGTT at 26 weeks of pregnancy is shown, with the IADPSG one-step thresholds marked at each time. How should the result be interpreted?

A 52-year-old man has a 75 g OGTT. His results, the tube used for each sample and the WHO 2-hour cut-offs are shown. In unseparated blood at room temperature, glucose falls by about 5-7% per hour. What should the laboratory do with the 2-hour result?

Refer to the 75 g oral glucose tolerance test shown, with the WHO cut-offs for the 2-hour value drawn. The fasting cut-off for diabetes is 7.0 mmol/L (126 mg/dL). The result is classified as: