A 31-year-old woman at 26 weeks of gestation had a 1-hour 50 g glucose challenge of 158 mg/dL [8.8 mmol/L]; the clinic's screening cut-off is 140 mg/dL [7.8 mmol/L]. Her HbA1c at 9 weeks was 5.3% [34 mmol/mol]. She returns fasting for a 100 g, 3-hour OGTT: fasting 97 mg/dL [5.4 mmol/L], 1 hour 174 mg/dL [9.7 mmol/L], 2 hours 159 mg/dL [8.8 mmol/L], 3 hours 128 mg/dL [7.1 mmol/L]. The clinic uses the Carpenter-Coustan thresholds: fasting 95, 1 hour 180, 2 hours 155 and 3 hours 140 mg/dL [5.3, 10.0, 8.6 and 7.8 mmol/L]. The correct interpretation is:

Not diagnostic: only one value is abnormal

Normal: the 1-hour value is below 180

Overt diabetes that predates pregnancy

A 47-year-old man with a BMI of 31 kg/m² and a family history of type 2 diabetes is screened at a wellness visit. He has no symptoms. From one fasting sample: HbA1c 6.7% [50 mmol/mol] by an NGSP-certified HPLC method with no hemoglobin variant peak, and fasting plasma glucose 114 mg/dL [6.3 mmol/L]. Hemoglobin 14.8 g/dL [148 g/L], MCV 88 fL, reticulocytes 1.1% and creatinine 1.0 mg/dL [88 µmol/L] are normal, and he has never been transfused. Using American Diabetes Association criteria, what is the most appropriate next step?

Repeat the HbA1c on a new sample

Diagnose diabetes from the HbA1c alone

Report prediabetes from the fasting glucose

Confirm diabetes with a fructosamine level

A 71-year-old man with a large fibrous tumor in the right chest has early-morning confusion that resolves with dextrose. During a symptomatic episode: plasma glucose 34 mg/dL [1.9 mmol/L], insulin below 1 µIU/mL [below 6 pmol/L], C-peptide below 0.2 ng/mL [below 0.07 nmol/L], proinsulin below 5 pmol/L, beta-hydroxybutyrate 0.3 mmol/L, cortisol 24 µg/dL [662 nmol/L], and a negative sulfonylurea screen. After 1 mg of intravenous glucagon, glucose rises by 42 mg/dL [2.3 mmol/L]. The laboratory notes that a beta-hydroxybutyrate of 2.7 mmol/L or less and a glucagon rise of 25 mg/dL [1.4 mmol/L] or more point to insulin-like activity. Which test is most likely to confirm the cause?

Selective arterial calcium stimulation

A child treated for diabetic ketoacidosis is improving, yet the urine ketone strip becomes more strongly positive. The best explanation is:

Beta-hydroxybutyrate is being oxidized to acetoacetate

Ketone production is rising despite insulin

The strip detects beta-hydroxybutyrate best

Acetoacetate is being reduced to beta-hydroxybutyrate

Carbohydrates: interpretation and disease correlation

24 ASCP MLS practice questions on Carbohydrates: interpretation and disease correlation, part of Chemistry. The first 24 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 31-year-old woman at 26 weeks of gestation had a 1-hour 50 g glucose challenge of 158 mg/dL [8.8 mmol/L]; the clinic's screening cut-off is 140 mg/dL [7.8 mmol/L]. Her HbA1c at 9 weeks was 5.3% [34 mmol/mol]. She returns fasting for a 100 g, 3-hour OGTT: fasting 97 mg/dL [5.4 mmol/L], 1 hour 174 mg/dL [9.7 mmol/L], 2 hours 159 mg/dL [8.8 mmol/L], 3 hours 128 mg/dL [7.1 mmol/L]. The clinic uses the Carpenter-Coustan thresholds: fasting 95, 1 hour 180, 2 hours 155 and 3 hours 140 mg/dL [5.3, 10.0, 8.6 and 7.8 mmol/L]. The correct interpretation is:
1. ANot diagnostic: only one value is abnormal
2. BNormal: the 1-hour value is below 180
3. CGestational diabetes mellitus
4. DOvert diabetes that predates pregnancy
Show answerHide answer
Answer: C · Gestational diabetes mellitus
In the two-step approach, a positive 50 g challenge is only a screen; the 100 g, 3-hour test makes the diagnosis. Gestational diabetes is diagnosed when two or more of the four values meet or exceed the thresholds. Here the fasting value (97 versus 95 mg/dL) and the 2-hour value (159 versus 155 mg/dL) are both abnormal, while the 1-hour and 3-hour values are not. A candidate who applies the nonpregnant fasting cut-off of 100 mg/dL misses the abnormal fasting result. Her normal HbA1c early in pregnancy makes diabetes that predates the pregnancy unlikely.
- A: The fasting 97 mg/dL counts: the pregnancy threshold is 95 mg/dL, not the nonpregnant 100 mg/dL.
- B: The 1-hour value is only one of four; the fasting and 2-hour values both meet their thresholds.
- D: Overt diabetes needs a fasting glucose of 126 mg/dL or more or an HbA1c of 6.5% or more; her early HbA1c was normal.
Question 2 · Hard
A 47-year-old man with a BMI of 31 kg/m² and a family history of type 2 diabetes is screened at a wellness visit. He has no symptoms. From one fasting sample: HbA1c 6.7% [50 mmol/mol] by an NGSP-certified HPLC method with no hemoglobin variant peak, and fasting plasma glucose 114 mg/dL [6.3 mmol/L]. Hemoglobin 14.8 g/dL [148 g/L], MCV 88 fL, reticulocytes 1.1% and creatinine 1.0 mg/dL [88 µmol/L] are normal, and he has never been transfused. Using American Diabetes Association criteria, what is the most appropriate next step?
1. ADiagnose diabetes from the HbA1c alone
2. BReport prediabetes from the fasting glucose
3. CConfirm diabetes with a fructosamine level
4. DRepeat the HbA1c on a new sample
Show answerHide answer
Answer: D · Repeat the HbA1c on a new sample
ADA cut points for diabetes are an HbA1c of 6.5% (48 mmol/mol) or more and a fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or more. Without clear hyperglycemia with symptoms, diagnosis needs two abnormal results: two different tests from the same sample, or the same test on two samples. Here the HbA1c is in the diabetes range but the fasting glucose is only in the prediabetes range (100-125 mg/dL), so the results are discordant. ADA advises repeating the test that is above its cut point, after considering interference; the normal blood count, absent variant and lack of transfusion make an HbA1c artifact unlikely. If the repeat HbA1c is again 6.5% or more, diabetes is diagnosed.
- A: In a patient without symptoms, a single abnormal result must be confirmed.
- B: The HbA1c is in the diabetes range, so the abnormal test must be repeated before he is classed.
- C: Fructosamine is not a diagnostic test for diabetes.
Question 3 · Hard
A 71-year-old man with a large fibrous tumor in the right chest has early-morning confusion that resolves with dextrose. During a symptomatic episode: plasma glucose 34 mg/dL [1.9 mmol/L], insulin below 1 µIU/mL [below 6 pmol/L], C-peptide below 0.2 ng/mL [below 0.07 nmol/L], proinsulin below 5 pmol/L, beta-hydroxybutyrate 0.3 mmol/L, cortisol 24 µg/dL [662 nmol/L], and a negative sulfonylurea screen. After 1 mg of intravenous glucagon, glucose rises by 42 mg/dL [2.3 mmol/L]. The laboratory notes that a beta-hydroxybutyrate of 2.7 mmol/L or less and a glucagon rise of 25 mg/dL [1.4 mmol/L] or more point to insulin-like activity. Which test is most likely to confirm the cause?
1. AIGF-2 to IGF-1 molar ratio
2. BSelective arterial calcium stimulation
3. C72-hour supervised fast
4. DCosyntropin stimulation test
Show answerHide answer
Answer: A · IGF-2 to IGF-1 molar ratio
Low ketones and a brisk glucagon response show that something is acting like insulin, yet insulin, C-peptide and proinsulin are all suppressed. That excludes insulinoma, sulfonylureas and injected insulin, and the adequate cortisol makes adrenal insufficiency unlikely. Large mesenchymal tumors can secrete incompletely processed ('big') IGF-2, which activates insulin receptors and suppresses insulin and growth hormone, so IGF-1 falls. An IGF-2 to IGF-1 molar ratio above about 10 supports non-islet cell tumor hypoglycemia. Removing the tumor cures it; glucose and glucocorticoids are used in the meantime.
- B: Calcium stimulation localizes an insulinoma, but insulin and C-peptide are suppressed here.
- C: Hypoglycemia has already been documented with a full set of results, so a prolonged fast adds nothing.
- D: Cortisol is adequate, and low ketones with a glucagon response argue against adrenal failure.
Question 4 · Medium
A child treated for diabetic ketoacidosis is improving, yet the urine ketone strip becomes more strongly positive. The best explanation is:
1. AKetone production is rising despite insulin
2. BThe strip detects beta-hydroxybutyrate best
3. CAcetoacetate is being reduced to beta-hydroxybutyrate
4. DBeta-hydroxybutyrate is being oxidized to acetoacetate
Show answerHide answer
Answer: D · Beta-hydroxybutyrate is being oxidized to acetoacetate
In DKA, most ketones are present as beta-hydroxybutyrate, which the nitroprusside strip does not detect. As insulin and fluids correct the acidosis, beta-hydroxybutyrate is oxidized to acetoacetate, which the strip detects well, so the strip can look worse while the patient improves. Blood beta-hydroxybutyrate is the better test for monitoring treatment. The ratio of beta-hydroxybutyrate to acetoacetate falls as the redox state returns to normal.
- A: Insulin suppresses ketone production, and the patient is improving.
- B: Nitroprusside reacts with acetoacetate (and weakly with acetone), not beta-hydroxybutyrate.
- C: Reduction to beta-hydroxybutyrate would make the strip less positive.
Question 5 · Medium
A non-pregnant adult has a 75 g OGTT with a fasting glucose of 96 mg/dL (5.3 mmol/L) and a 2-hour glucose of 168 mg/dL (9.3 mmol/L). These results indicate:
1. AImpaired glucose tolerance
2. BImpaired fasting glucose
3. CNormal glucose tolerance
4. DDiabetes mellitus
Show answerHide answer
Answer: A · Impaired glucose tolerance
The fasting value is below 100 mg/dL (5.6 mmol/L), so fasting glucose is normal. The 2-hour value falls between 140 and 199 mg/dL (7.8 to 11.0 mmol/L), which defines impaired glucose tolerance. This is a form of prediabetes with a higher risk of diabetes and cardiovascular disease. Diabetes would need a 2-hour value of 200 mg/dL (11.1 mmol/L) or more.
- B: Impaired fasting glucose needs a fasting value of 100 to 125 mg/dL.
- C: A 2-hour value of 140 mg/dL or more is not normal.
- D: Diabetes needs a 2-hour value of 200 mg/dL or more, or a fasting value of 126 mg/dL or more.
Question 6 · Medium
Which condition tends to raise hemoglobin A1c without any change in average glucose?
1. ARecent acute blood loss
2. BTreatment with erythropoietin
3. CUntreated iron deficiency anemia
4. DHereditary spherocytosis
Answer and explanation in LearnFree account
Question 7 · Hard
During a supervised fast, a 58-year-old woman without diabetes has symptoms with a glucose of 41 mg/dL (2.3 mmol/L). Insulin, C-peptide and proinsulin are all raised, beta-hydroxybutyrate is low, insulin antibodies are negative, and the drug screen detects glipizide. The most likely cause is:
1. AInsulin autoimmune syndrome
2. BExogenous insulin injection
3. CSulfonylurea ingestion
4. DInsulinoma
Answer and explanation in LearnFree account
Question 8 · Hard
A patient with chronic lymphocytic leukemia (WBC 260 x 10^3/µL [260 x 10^9/L]) feels well. A glucose drawn into a lithium heparin tube, left unspun and analyzed 3 hours later, is 32 mg/dL (1.8 mmol/L); a bedside meter reading at the time of the draw was 98 mg/dL (5.4 mmol/L). The best explanation is:
1. AHeparin inhibiting the glucose reagent
2. BTrue hypoglycemia missed by the meter
3. CAn insulin-like factor from the leukemia
4. DIn vitro glycolysis by the leukocytes
Answer and explanation in LearnFree account
Question 9 · Hard
An adult has fasting glucose values of 162 mg/dL (9.0 mmol/L) and 171 mg/dL (9.5 mmol/L) on two days, but an HbA1c of 5.1% (32 mmol/mol). Reticulocytes are 9% and haptoglobin is below 10 mg/dL (0.1 g/L). The best interpretation is:
1. APrediabetes; repeat the HbA1c in one year
2. BNo diabetes; the normal HbA1c rules it out
3. CDiabetes; HbA1c falsely low from hemolysis
4. DDiabetes is unproven until an OGTT is done
Answer and explanation in LearnFree account
Question 10 · Medium
Compared with diabetic ketoacidosis, hyperosmolar hyperglycemic state typically shows:
1. ALower glucose and heavy ketosis
2. BHigher glucose and little ketosis
3. CLower osmolality and more ketones
4. DNormal glucose and severe acidosis
Answer and explanation in LearnFree account
Question 11 · Hard
A 34-year-old nurse without diabetes is confused, with a plasma glucose of 38 mg/dL (2.1 mmol/L). Blood drawn during the episode shows insulin markedly raised, C-peptide undetectable, proinsulin low and a negative sulfonylurea screen. What is the most likely cause?
1. AAdrenal insufficiency
2. BSulfonylurea ingestion
3. CInjection of insulin
4. DAn insulinoma
Answer and explanation in LearnFree account
Question 12 · Hard
A 40-year-old who had followed a very low-carbohydrate diet for 2 weeks has a 75 g OGTT 2-hour glucose of 176 mg/dL (9.8 mmol/L). Fasting glucose and HbA1c are normal. What should the laboratory advise?
1. AReport impaired glucose tolerance as found
2. BRepeat the test with a 100 g glucose load
3. CRepeat after a longer fast of 16 hours
4. DRepeat after 3 days of normal carbohydrate intake
Answer and explanation in LearnFree account
Question 13 · Medium
Which single finding is enough to diagnose diabetes without a second confirming result?
1. ARandom glucose 240 mg/dL (13.3 mmol/L) with polyuria
2. B2-hour OGTT glucose 185 mg/dL (10.3 mmol/L)
3. CFasting glucose 132 mg/dL (7.3 mmol/L), no symptoms
4. DHbA1c 6.7% (50 mmol/mol), no symptoms
Answer and explanation in LearnFree account
Question 14 · Hard
A 4.6 kg baby is born to a mother with poorly controlled diabetes. At 2 hours of age the baby's plasma glucose is 28 mg/dL (1.6 mmol/L). What is the main cause of this hypoglycemia?
1. AMaternal insulin crossing the placenta to the baby
2. BLow cortisol from neonatal adrenal failure
3. CFetal hyperinsulinism from maternal glucose
4. DInherited glucose-6-phosphatase deficiency
Answer and explanation in LearnFree account
Question 15 · Easy
In a 75 g oral glucose tolerance test in a non-pregnant adult, the 2-hour plasma glucose threshold for diabetes is:
1. A153 mg/dL (8.5 mmol/L)
2. B126 mg/dL (7.0 mmol/L)
3. C140 mg/dL (7.8 mmol/L)
4. D200 mg/dL (11.1 mmol/L)
Answer and explanation in LearnFree account
Question 16 · Easy
With an NGSP-certified method, which hemoglobin A1c value is the threshold for diagnosing diabetes?
1. A7.0% (53 mmol/mol)
2. B6.5% (48 mmol/mol)
3. C5.7% (39 mmol/mol)
4. D6.0% (42 mmol/mol)
Answer and explanation in LearnFree account
Question 17 · Hard
A 52-year-old with type 2 diabetes takes empagliflozin and had surgery 2 days ago. Results: glucose 178 mg/dL (9.9 mmol/L), pH 7.19, bicarbonate 11 mmol/L, beta-hydroxybutyrate 5.6 mmol/L (reference < 0.6), lactate 1.2 mmol/L. What is the most likely diagnosis?
1. AEuglycemic diabetic ketoacidosis
2. BStarvation ketosis after surgery
3. CLactic acidosis from metformin
4. DHyperosmolar hyperglycemic state
Answer and explanation in LearnFree account
Question 18 · Hard
A thin 50-year-old man is brought in confused after two days of heavy drinking with little food. Plasma glucose is 36 mg/dL (2.0 mmol/L), and insulin and C-peptide are suppressed. What is the main reason for his hypoglycemia?
1. AEthanol speeds glucose uptake by muscle
2. BEthanol blocks hepatic gluconeogenesis
3. CEthanol blocks intestinal glucose absorption
4. DEthanol stimulates insulin release
Answer and explanation in LearnFree account
Question 19 · Easy
Whipple's triad, used to confirm true hypoglycemia, is symptoms of hypoglycemia, a low plasma glucose and:
1. ARelief of symptoms when glucose is raised
2. BNo rise in glucose after glucagon
3. CKetones in the blood during the episode
4. DA raised insulin level during the episode
Answer and explanation in LearnFree account
Question 20 · Medium
In a patient with sickle cell anemia (Hb SS) and type 2 diabetes, which test is best for monitoring average glucose?
1. AUrine glucose
2. BC-peptide
3. CFructosamine
4. DHemoglobin A1c
Answer and explanation in LearnFree account
Question 21 · Hard
At 26 weeks, a pregnant woman has a one-step 75 g OGTT: fasting 86 mg/dL (4.8 mmol/L), 1 hour 172 mg/dL (9.5 mmol/L), 2 hours 158 mg/dL (8.8 mmol/L). How should these results be interpreted?
1. AGestational diabetes
2. BImpaired fasting glucose
3. CNormal glucose tolerance
4. DOvert diabetes in pregnancy
Answer and explanation in LearnFree account
Question 22 · Medium
Refer to the 75 g oral glucose tolerance test shown, from a non-pregnant adult. By ADA criteria, how is the result classified?
Figure: MedExams
1. APrediabetes by the 2-hour value only
2. BPrediabetes by the fasting value only
3. CDiabetes mellitus by the 2-hour value
4. DPrediabetes by both fasting and 2-hour values
Answer and explanation in LearnFree account
Question 23 · Hard
A 26-year-old woman reports shakiness and sweating 2 to 3 hours after meals. Her physician orders the 5-hour 75 g oral glucose tolerance test shown, and she has no symptoms at any point during it. The best interpretation is:
Figure: MedExams
1. AFasting hypoglycemia from an insulinoma
2. BPostprandial hypoglycemia is confirmed
3. CNot diagnostic: Whipple's triad is not met
4. DImpaired glucose tolerance
Answer and explanation in LearnFree account
Question 24 · Medium
Hemoglobin A1c reflects average blood glucose over approximately which period?
1. AThe previous 12 months
2. BThe previous 2 to 3 months
3. CThe previous 2 to 3 weeks
4. DThe previous 24 hours
Answer and explanation in LearnFree account

Carbohydrates: interpretation and disease correlation

A child treated for diabetic ketoacidosis is improving, yet the urine ketone strip becomes more strongly positive. The best explanation is:

A non-pregnant adult has a 75 g OGTT with a fasting glucose of 96 mg/dL (5.3 mmol/L) and a 2-hour glucose of 168 mg/dL (9.3 mmol/L). These results indicate:

Which condition tends to raise hemoglobin A1c without any change in average glucose?

During a supervised fast, a 58-year-old woman without diabetes has symptoms with a glucose of 41 mg/dL (2.3 mmol/L). Insulin, C-peptide and proinsulin are all raised, beta-hydroxybutyrate is low, insulin antibodies are negative, and the drug screen detects glipizide. The most likely cause is:

An adult has fasting glucose values of 162 mg/dL (9.0 mmol/L) and 171 mg/dL (9.5 mmol/L) on two days, but an HbA1c of 5.1% (32 mmol/mol). Reticulocytes are 9% and haptoglobin is below 10 mg/dL (0.1 g/L). The best interpretation is:

Compared with diabetic ketoacidosis, hyperosmolar hyperglycemic state typically shows:

A 34-year-old nurse without diabetes is confused, with a plasma glucose of 38 mg/dL (2.1 mmol/L). Blood drawn during the episode shows insulin markedly raised, C-peptide undetectable, proinsulin low and a negative sulfonylurea screen. What is the most likely cause?

A 40-year-old who had followed a very low-carbohydrate diet for 2 weeks has a 75 g OGTT 2-hour glucose of 176 mg/dL (9.8 mmol/L). Fasting glucose and HbA1c are normal. What should the laboratory advise?

Which single finding is enough to diagnose diabetes without a second confirming result?

A 4.6 kg baby is born to a mother with poorly controlled diabetes. At 2 hours of age the baby's plasma glucose is 28 mg/dL (1.6 mmol/L). What is the main cause of this hypoglycemia?

In a 75 g oral glucose tolerance test in a non-pregnant adult, the 2-hour plasma glucose threshold for diabetes is:

With an NGSP-certified method, which hemoglobin A1c value is the threshold for diagnosing diabetes?

A 52-year-old with type 2 diabetes takes empagliflozin and had surgery 2 days ago. Results: glucose 178 mg/dL (9.9 mmol/L), pH 7.19, bicarbonate 11 mmol/L, beta-hydroxybutyrate 5.6 mmol/L (reference < 0.6), lactate 1.2 mmol/L. What is the most likely diagnosis?

A thin 50-year-old man is brought in confused after two days of heavy drinking with little food. Plasma glucose is 36 mg/dL (2.0 mmol/L), and insulin and C-peptide are suppressed. What is the main reason for his hypoglycemia?

Whipple's triad, used to confirm true hypoglycemia, is symptoms of hypoglycemia, a low plasma glucose and:

In a patient with sickle cell anemia (Hb SS) and type 2 diabetes, which test is best for monitoring average glucose?

At 26 weeks, a pregnant woman has a one-step 75 g OGTT: fasting 86 mg/dL (4.8 mmol/L), 1 hour 172 mg/dL (9.5 mmol/L), 2 hours 158 mg/dL (8.8 mmol/L). How should these results be interpreted?

Refer to the 75 g oral glucose tolerance test shown, from a non-pregnant adult. By ADA criteria, how is the result classified?

A 26-year-old woman reports shakiness and sweating 2 to 3 hours after meals. Her physician orders the 5-hour 75 g oral glucose tolerance test shown, and she has no symptoms at any point during it. The best interpretation is:

Hemoglobin A1c reflects average blood glucose over approximately which period?