A 9-year-old boy has had anemia and jaundice since birth, needed an exchange transfusion as a newborn, and now has splenomegaly and gallstones. His hemolysis is continuous rather than in episodes, with no link to drugs, fava beans or infections. His last transfusion was 6 months ago. Results: hemoglobin 92 g/L (9.2 g/dL), MCV 99 fL, reticulocytes 11%, DAT negative, eosin-5'-maleimide (EMA) binding normal and HPLC normal. The film shows polychromasia but no spherocytes. Quantitative G6PD activity is 0.3 U/g Hb (adjusted male median 8.0 U/g Hb), and pyruvate kinase activity is above its reference range. The most likely diagnosis is:

A severe G6PD variant causing chronic hemolysis

A common G6PD variant with episodic hemolysis

In August, a health centre sends 24 EDTA samples for the G6PD fluorescent spot test. The courier box had no cool packs, was left in a vehicle, and reached the laboratory 36 hours after collection, warm to the touch. Nine samples (37%) show no or very weak fluorescence, and six of these are from women; all nine have normal hemoglobin and reticulocyte counts. The normal and deficient controls run with the batch give the expected results. This centre's usual rate of deficient results is about 8%, almost all in boys and men. What is the most likely explanation, and what should be done?

Heat has inactivated the enzyme; recollect the samples

The results are valid; report them as deficient

Reagent has deteriorated; repeat the batch with new kits

EDTA has inhibited the enzyme; recollect in heparin

Methylene blue is a poor treatment for methemoglobinemia in a patient with severe G6PD deficiency, because it:

Needs NADPH to be reduced to its active form

Converts methemoglobin into sulfhemoglobin

Inhibits cytochrome b5 reductase in red cells

Is broken down by the G6PD enzyme itself

In the reference spectrophotometric assay for G6PD, enzyme activity is measured as:

A rise in absorbance at 340 nm as NADPH forms

A fall in absorbance at 340 nm as NADH is used

A fall in absorbance at 340 nm as NADPH is used

A rise in absorbance at 540 nm as cyanmethemoglobin forms

G6PD deficiency and red cell enzyme defects

15 DOH Abu Dhabi (HAAD) lab licensing practice questions on G6PD deficiency and red cell enzyme defects, part of Hematology. The first 15 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 9-year-old boy has had anemia and jaundice since birth, needed an exchange transfusion as a newborn, and now has splenomegaly and gallstones. His hemolysis is continuous rather than in episodes, with no link to drugs, fava beans or infections. His last transfusion was 6 months ago. Results: hemoglobin 92 g/L (9.2 g/dL), MCV 99 fL, reticulocytes 11%, DAT negative, eosin-5'-maleimide (EMA) binding normal and HPLC normal. The film shows polychromasia but no spherocytes. Quantitative G6PD activity is 0.3 U/g Hb (adjusted male median 8.0 U/g Hb), and pyruvate kinase activity is above its reference range. The most likely diagnosis is:
1. AA common G6PD variant with episodic hemolysis
2. BPyruvate kinase deficiency
3. CHereditary spherocytosis
4. DA severe G6PD variant causing chronic hemolysis
Show answerHide answer
Answer: D · A severe G6PD variant causing chronic hemolysis
G6PD activity of about 4% of the male median (0.3 ÷ 8.0), measured 6 months after the last transfusion and despite 11% reticulocytes, confirms severe deficiency. Most G6PD variants, including the Mediterranean type common in the Gulf, cause hemolysis only after oxidant stress such as fava beans, drugs or infection. Continuous hemolysis from birth without triggers is chronic nonspherocytic hemolytic anemia caused by a rare severe variant (formerly WHO class I), in which red cells are destroyed even under everyday oxidant load. The raised PK activity reflects the young red cell population and argues against PK deficiency, and normal EMA binding with no spherocytes argues against hereditary spherocytosis. He should still avoid oxidant drugs and fava beans, which make the hemolysis worse.
- A: Common variants cause hemolysis only after triggers, not continuously from birth.
- B: PK activity is raised, as expected from the many young red cells.
- C: EMA binding is normal and the film shows no spherocytes.
Question 2 · Hard
In August, a health centre sends 24 EDTA samples for the G6PD fluorescent spot test. The courier box had no cool packs, was left in a vehicle, and reached the laboratory 36 hours after collection, warm to the touch. Nine samples (37%) show no or very weak fluorescence, and six of these are from women; all nine have normal hemoglobin and reticulocyte counts. The normal and deficient controls run with the batch give the expected results. This centre's usual rate of deficient results is about 8%, almost all in boys and men. What is the most likely explanation, and what should be done?
1. AHeat has inactivated the enzyme; recollect the samples
2. BThe results are valid; report them as deficient
3. CReagent has deteriorated; repeat the batch with new kits
4. DEDTA has inhibited the enzyme; recollect in heparin
Show answerHide answer
Answer: A · Heat has inactivated the enzyme; recollect the samples
The deficient rate is more than four times the centre's usual rate, and most of the extra deficient results are in women, who need two deficient X chromosomes (or very skewed X inactivation) to test as deficient and so are affected far less often than men. Because both controls behaved correctly, the reagents and the UV lamp are working, so the fault lies in the samples. G6PD activity falls in whole blood kept warm for a long time, and a sample that loses enough activity makes too little NADPH to fluoresce, giving a falsely deficient result. Samples should travel cool (2-8 °C) and be tested promptly, so these should be recollected rather than reported. EDTA is a suitable anticoagulant for the test.
- B: A cluster of deficient women and a rate four times the usual one point to a sample problem.
- C: Both controls gave the expected results, so the reagents are working.
- D: EDTA is a suitable anticoagulant for G6PD testing.
Question 3 · Medium
Methylene blue is a poor treatment for methemoglobinemia in a patient with severe G6PD deficiency, because it:
1. AConverts methemoglobin into sulfhemoglobin
2. BNeeds NADPH to be reduced to its active form
3. CInhibits cytochrome b5 reductase in red cells
4. DIs broken down by the G6PD enzyme itself
Show answerHide answer
Answer: B · Needs NADPH to be reduced to its active form
Methylene blue works only after an NADPH-dependent reductase converts it to leucomethylene blue, which then reduces methemoglobin back to hemoglobin. G6PD is the red cell's main source of NADPH, so in severe deficiency the drug is not activated. Methylene blue is also an oxidant and can itself trigger hemolysis in these patients. Knowing the G6PD status before it is given is therefore important where deficiency is common.
- A: Sulfhemoglobin is formed by some drugs and sulfur compounds, not by methylene blue.
- C: Methylene blue does not inhibit cytochrome b5 reductase; inherited lack of that enzyme is a separate cause of methemoglobinemia.
- D: G6PD acts on glucose-6-phosphate, not on methylene blue.
Question 4 · Easy
Before primaquine is given to clear the liver stages of Plasmodium vivax, WHO advises testing for:
1. AHereditary spherocytosis
2. BSickle cell trait
3. CG6PD deficiency
4. DPyruvate kinase deficiency
Show answerHide answer
Answer: C · G6PD deficiency
Primaquine clears the dormant liver hypnozoites of P. vivax but is a strong oxidant that can cause severe hemolysis in G6PD-deficient people. WHO therefore advises that G6PD status guide its use, with a changed regimen or avoidance in deficient patients. Tafenoquine, a related drug, needs a quantitative test showing at least 70% of normal activity. Laboratories that see imported malaria should be able to offer G6PD testing quickly.
- A: Hereditary spherocytosis is a membrane defect, and primaquine is not a known trigger.
- B: Sickle cell trait does not cause hemolysis with primaquine.
- D: Pyruvate kinase deficiency is a glycolytic defect that primaquine does not worsen.
Question 5 · Medium
In the reference spectrophotometric assay for G6PD, enzyme activity is measured as:
1. AA fall in absorbance at 340 nm as NADH is used
2. BA fall in absorbance at 340 nm as NADPH is used
3. CA rise in absorbance at 540 nm as cyanmethemoglobin forms
4. DA rise in absorbance at 340 nm as NADPH forms
Show answerHide answer
Answer: D · A rise in absorbance at 340 nm as NADPH forms
A hemolysate is mixed with glucose-6-phosphate and NADP+, and G6PD converts the NADP+ to NADPH. NADPH absorbs light at 340 nm, so activity is the rate at which absorbance rises. The result is divided by the hemoglobin of the hemolysate and reported in U/g Hb at a stated temperature. Some methods also correct for 6-phosphogluconate dehydrogenase, which makes extra NADPH in the same reaction mix.
- A: A falling NADH signal belongs to assays such as LD (pyruvate to lactate) or AST, not G6PD.
- B: NADPH is produced, not used, so absorbance rises.
- C: Cyanmethemoglobin at 540 nm measures hemoglobin, which is used only to express the result per gram of hemoglobin.
Question 6 · Medium
The mother of a G6PD-deficient boy has a normal fluorescent spot test. Why does this not rule out that she is a carrier?
1. AThe spot test is valid only on newborn samples
2. BHer normal red cells can mask the deficient ones
3. CSons inherit the G6PD gene from their father
4. DThe spot test detects only the A- variant
Answer and explanation in LearnFree account
Question 7 · Hard
A laboratory's adjusted male median G6PD activity (taken as 100%) is 8.0 U/g Hb. It reports below 30% as deficient, 30-80% as intermediate and above 80% as normal. A woman's activity is 3.6 U/g Hb. How is her result reported?
1. A222%, normal activity
2. B45%, intermediate activity
3. C45%, deficient activity
4. D55%, intermediate activity
Answer and explanation in LearnFree account
Question 8 · Easy
Severe G6PD deficiency is seen mostly in males because the G6PD gene is:
1. ALocated on the Y chromosome
2. BLocated in mitochondrial DNA
3. CLocated on chromosome 11
4. DLocated on the X chromosome
Answer and explanation in LearnFree account
Question 9 · Hard
A 4-year-old boy whose brother has G6PD deficiency had acute hemolysis with a fever and received a red cell transfusion 3 weeks ago. Now hemoglobin is 112 g/L (11.2 g/dL), reticulocytes 1.5% (reference 0.5-2.5%) and WBC 8.0 × 10^9/L. His G6PD activity is 70% of the male median. The most likely explanation is:
1. AHis leukocytes have raised the result
2. BHis reticulocytes have raised the result
3. CDonor red cells are still circulating
4. DHe is a heterozygous carrier
Answer and explanation in LearnFree account
Question 10 · Hard
A 3-day-old term boy has total bilirubin 310 µmol/L (18.1 mg/dL), with conjugated bilirubin 9 µmol/L (0.5 mg/dL). Mother and baby are both group A, D positive, and the DAT is negative. Hemoglobin is 168 g/L (16.8 g/dL), reticulocytes are within the range for age and the film shows no spherocytes. Which test should be done next?
1. AHemoglobin HPLC for HbS
2. BMaternal antibody screen
3. COsmotic fragility test
4. DQuantitative G6PD assay
Answer and explanation in LearnFree account
Question 11 · Medium
Compared with pyruvate kinase deficiency, typical G6PD deficiency is more likely to show:
1. AAutosomal recessive inheritance
2. BContinuous hemolysis from early childhood
3. CA raised red cell 2,3-BPG level
4. DEpisodic hemolysis after oxidant exposure
Answer and explanation in LearnFree account
Question 12 · Hard
A 5-year-old boy has pallor and dark urine 2 days after eating fava beans. Hemoglobin is 72 g/L (7.2 g/dL), reticulocytes 12%, the DAT is negative and the film shows bite and blister cells. The G6PD fluorescent spot test fluoresces brightly. What should the laboratory advise?
1. ARepeat G6PD testing about 3 months after recovery
2. BReport that G6PD deficiency has been excluded
3. CRepeat the DAT with monospecific anti-C3 reagent
4. DInvestigate for hereditary spherocytosis instead
Answer and explanation in LearnFree account
Question 13 · Easy
In the Gulf region, hemolysis in G6PD-deficient newborns has been linked to which traditional practice?
1. AApplying kohl around the eyes
2. BApplying henna to the skin
3. CMassaging with olive oil
4. DGiving honey by mouth
Answer and explanation in LearnFree account
Question 14 · Medium
A child develops sudden hemolysis after eating fava beans. The blood film shows bite cells and blister cells. What is the most likely cause?
1. AHereditary spherocytosis
2. BSickle cell crisis
3. CG6PD deficiency
4. DIron deficiency anemia
Answer and explanation in LearnFree account
Question 15 · Hard
Why can a G6PD activity test done during an acute hemolytic episode give a falsely normal result?
1. AThe test only works on frozen blood samples
2. BOld deficient cells are gone; young cells have more G6PD
3. CEDTA in the tube inactivates the G6PD enzyme
4. DHemolysis releases extra G6PD from the patient's platelets
Answer and explanation in LearnFree account

G6PD deficiency and red cell enzyme defects

Methylene blue is a poor treatment for methemoglobinemia in a patient with severe G6PD deficiency, because it:

Before primaquine is given to clear the liver stages of Plasmodium vivax, WHO advises testing for:

In the reference spectrophotometric assay for G6PD, enzyme activity is measured as:

The mother of a G6PD-deficient boy has a normal fluorescent spot test. Why does this not rule out that she is a carrier?

A laboratory's adjusted male median G6PD activity (taken as 100%) is 8.0 U/g Hb. It reports below 30% as deficient, 30-80% as intermediate and above 80% as normal. A woman's activity is 3.6 U/g Hb. How is her result reported?

Severe G6PD deficiency is seen mostly in males because the G6PD gene is:

Compared with pyruvate kinase deficiency, typical G6PD deficiency is more likely to show:

A 5-year-old boy has pallor and dark urine 2 days after eating fava beans. Hemoglobin is 72 g/L (7.2 g/dL), reticulocytes 12%, the DAT is negative and the film shows bite and blister cells. The G6PD fluorescent spot test fluoresces brightly. What should the laboratory advise?

In the Gulf region, hemolysis in G6PD-deficient newborns has been linked to which traditional practice?

A child develops sudden hemolysis after eating fava beans. The blood film shows bite cells and blister cells. What is the most likely cause?

Why can a G6PD activity test done during an acute hemolytic episode give a falsely normal result?