Methemoglobin and Abnormal Hemoglobins — MCQs

10 questions

A child presents with recurrent chest infections and abdominal pain. There is a history of 1 blood transfusion in the past. On examination, he had icterus and mild splenomegaly. Electrophoresis shows increased HbA2, HbF, and S spike. What is the likely diagnosis?

Which of the following statements is MOST accurate regarding cyanosis in methemoglobinemia?

Which of the following conditions is the classic example of acute intravascular hemolysis triggered by oxidative stress?

Which local anaesthetic is known to cause methemoglobinemia?

Which of the following is a feature not typically associated with Hereditary Spherocytosis?

All true about interaction of SpO2 reading and methemoglobinemia, except:

A 30-year-old male presents with hypoxia, cyanosis, and confusion. He is found to have methemoglobinemia. What is the most appropriate treatment?

Persons with heterozygous sickle cell trait are protected from infection by:

All of the following are true about glutathione, except:

Q10

In which type of hemoglobin are zeta 2 and gamma 2 chains present?

Methemoglobin and Abnormal Hemoglobins Indian Medical PG Practice Questions and MCQs

Question 1: A child presents with recurrent chest infections and abdominal pain. There is a history of 1 blood transfusion in the past. On examination, he had icterus and mild splenomegaly. Electrophoresis shows increased HbA2, HbF, and S spike. What is the likely diagnosis?

A. HbC disease
B. Sickle cell disease
C. Aplastic anemia
D. Sickle Beta Thalassemia (Correct Answer)

Explanation: ***Sickle Beta Thalassemia*** - The combination of **sickle cell disease manifestations** (recurrent chest infections, abdominal pain, icterus, splenomegaly) with **electrophoresis showing increased HbA2, elevated HbF, and S spike** is diagnostic of **Sickle Beta Thalassemia**. - **Increased HbA2 (>3.5%)** is the key distinguishing feature that differentiates this from pure sickle cell disease. It indicates co-inheritance of a **beta-thalassemia gene** along with the **sickle cell gene**. - Clinical presentation is similar to sickle cell disease with **vaso-occlusive crises**, **acute chest syndrome**, hemolytic anemia, and organomegaly. - The severity depends on the type: S/β⁰-thalassemia (no HbA production) is clinically more severe and similar to SS disease, while S/β⁺-thalassemia (reduced HbA) tends to be milder. *Sickle cell disease* - Pure sickle cell disease (HbSS) presents with similar clinical features: recurrent chest infections, abdominal pain, hemolysis, and splenomegaly. - However, electrophoresis would show **normal or only slightly elevated HbA2 (2-3%)**, not the increased HbA2 mentioned in this case. - The presence of significantly increased HbA2 rules out pure sickle cell disease. *HbC disease* - Patients with HbC disease typically have **mild chronic hemolytic anemia** and **splenomegaly** but usually lack severe vaso-occlusive crises. - Electrophoresis would show primarily **HbC**, not an S spike. - The clinical picture is much milder than described in this case. *Aplastic anemia* - Characterized by **pancytopenia** due to bone marrow failure, leading to fatigue, infections, and bleeding tendency. - Does not involve hemolysis, icterus, or abnormal hemoglobin variants on electrophoresis. - The electrophoresis findings completely exclude this diagnosis.

Question 2: Which of the following statements is MOST accurate regarding cyanosis in methemoglobinemia?

A. Always associated with tachycardia
B. Caused by increased carboxyhemoglobin levels
C. Does not improve with supplemental oxygen (Correct Answer)
D. Can occur in both congenital and acquired forms of the disease.

Explanation: ***Does not improve with supplemental oxygen*** - In **methemoglobinemia**, the iron in hemoglobin is oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state, making it unable to bind oxygen. [1] - Therefore, despite supplemental oxygen, the **abnormal methemoglobin** cannot carry more oxygen, leading to persistent cyanosis. *Always associated with tachycardia* - While methemoglobinemia can cause **hypoxia** and compensatory **tachycardia**, it is not *always* present, especially in mild cases or if other coexisting conditions blunt the response. - The primary mechanism of cyanosis is the presence of **deoxygenated methemoglobin**, not solely the body's compensatory responses. [1] *Caused by increased carboxyhemoglobin levels* - **Carboxyhemoglobinemia** is caused by carbon monoxide poisoning, where carbon monoxide binds to hemoglobin with high affinity, preventing oxygen transport. - Methemoglobinemia is a distinct condition involving the **oxidation of iron** in hemoglobin to the ferric state. *Can occur in both congenital and acquired forms of the disease.* - This statement is generally true about methemoglobinemia itself (it can be congenital or acquired), but it doesn't directly explain the **characteristic cyanosis** and its resistance to oxygen. [1] - The question asks what is *most accurate regarding cyanosis* in the context of methemoglobinemia, focusing on the physiological manifestation rather than the disease etiology.

Question 3: Which of the following conditions is the classic example of acute intravascular hemolysis triggered by oxidative stress?

A. Hereditary spherocytosis
B. Sickle cell disease
C. Acute G6PD deficiency (Correct Answer)
D. None of the options

Explanation: ***b and c*** - Intravascular hemolysis is commonly associated with both **Acute G6PD deficiency** and **Hereditary spherocytosis**, leading to destruction of red blood cells in the bloodstream [1]. - These conditions are characterized by **high levels of hemoglobinuria** and **low haptoglobin**, indicative of intravascular hemolysis. *Sickle cell ds* - Sickle cell disease primarily causes **extravascular hemolysis** due to splenic sequestration rather than **intravascular** destruction [3]. - The clinical features include **vaso-occlusive crises** and splenic infarction rather than hemolysis within the blood vessels. *Acute G6PD* - While acute G6PD deficiency can lead to hemolysis, it is typically **triggered by oxidative stress** rather than occurring continuously [2]. - The hemolysis in G6PD deficiency occurs more in an **extravascular** manner unless acute stress occurs, which can result in **acute intravascular hemolysis, marked by anemia, hemoglobinemia, and hemoglobinuria** [4]. *Hereditary spherocytosis* - This condition primarily causes **extravascular hemolysis** through the spleen, where abnormal spherocytes are destroyed [1]. - Although it leads to anemia, the hallmark of hereditary spherocytosis is the **spleen's role** in hemocyte destruction rather than intravascular hemolysis.

Question 4: Which local anaesthetic is known to cause methemoglobinemia?

A. Procaine
B. Prilocaine (Correct Answer)
C. Ropivacaine
D. Etidocaine

Explanation: ***Prilocaine*** - **Prilocaine** is metabolized into **ortho-toluidine**, which can oxidize hemoglobin to **methemoglobin**, especially at higher doses or in susceptible individuals. - **Methemoglobinemia** symptoms include **cyanosis**, **dyspnea**, and in severe cases, central nervous system depression, due to reduced oxygen-carrying capacity of blood. *Procaine* - **Procaine** is an ester-type local anesthetic. It is metabolized to **para-aminobenzoic acid (PABA)**, which can cause allergic reactions, but it is not associated with methemoglobinemia. - It has a relatively **short duration of action** and is less commonly used now compared to amide-type local anesthetics. *Etidocaine* - **Etidocaine** is an amide-type local anesthetic that is known for its **long duration of action** and high potency. - While it can cause systemic toxicity with high doses due to its cardiac and neurological effects, **methemoglobinemia** is not a characteristic side effect. *Ropivacaine* - **Ropivacaine** is an amide-type local anesthetic similar to bupivacaine, known for its **motor-sparing effect** and use in regional anesthesia. - It is associated with a lower risk of **cardiotoxicity** compared to bupivacaine but does not cause methemoglobinemia.

Question 5: Which of the following is a feature not typically associated with Hereditary Spherocytosis?

A. Gall stones
B. Direct Coombs Positive (Correct Answer)
C. Splenomegaly
D. Increased Osmotic Fragility

Explanation: ***Direct Coomb's Positive*** - In Hereditary Spherocytosis, the **Coomb's test** is typically **negative**, indicating that hemolysis is not due to autoimmune factors. - Presence of **spherocytes** on the blood smear and increased fragility are hallmark findings, not antibodies against red cells [1]. *Splenomegaly* - **Splenomegaly** is common in Hereditary Spherocytosis as the spleen actively removes abnormal spherocytes from circulation [1]. - It can lead to **hypersplenism**, with resultant anemia and thrombocytopenia. *Increased Osmotic Fragility* - Increased osmotic fragility is a key feature of Hereditary Spherocytosis, as red blood cells are less able to withstand hypotonic solutions [1]. - This results from a defect in the red cell membrane, causing spherocyte shape and fragility. *Gall stones* - Patients may develop **gallstones** due to increased bilirubin from the breakdown of spherocytes, leading to **bilirubin stones** [1]. - Gallstones are a common complication due to chronic hemolysis. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 597-598.

Question 6: All true about interaction of SpO2 reading and methemoglobinemia, except:

A. Increase in MetHb produces an overestimation when true SpO2 <85%
B. Does not get affected in Methemoglobinaemia (Correct Answer)
C. MetHb absorbs red and infrared wavelength of light in a 1:1 ratio corresponding
D. Increase in MetHb produces an underestimation when true SpO2 >85%

Explanation: ***Correct: Does not get affected in Methemoglobinemia*** - This statement is **FALSE**, making it the correct answer for this EXCEPT question - **Methemoglobinemia significantly affects SpO2 readings** due to MetHb's optical properties - Pulse oximeters cannot distinguish methemoglobin from oxyhemoglobin and deoxyhemoglobin, leading to **inaccurate measurements** - As MetHb levels rise, the SpO2 reading tends to **plateau around 85%** regardless of true oxygen saturation *Incorrect: Increase in MetHb produces an overestimation when true SpO2 <85%* - This statement is TRUE - When **actual SpO2 is below 85%** and MetHb is elevated, the pulse oximeter reads **higher than the true value** (overestimation) - This occurs because MetHb absorption characteristics cause the reading to gravitate toward 85% *Incorrect: MetHb absorbs red and infrared wavelength of light in a 1:1 ratio* - This statement is TRUE - **Methemoglobin** has similar extinction coefficients at both **660 nm (red)** and **940 nm (infrared)** wavelengths - This 1:1 absorption ratio corresponds to an SpO2 reading of approximately **85%** on conventional pulse oximeters - This is why SpO2 readings plateau at 85% in methemoglobinemia regardless of true saturation *Incorrect: Increase in MetHb produces an underestimation when true SpO2 >85%* - This statement is TRUE - When **actual SpO2 is above 85%** and MetHb is elevated, the pulse oximeter reads **lower than the true value** (underestimation) - The reading is pulled down toward the 85% plateau created by MetHb's absorption characteristics

Question 7: A 30-year-old male presents with hypoxia, cyanosis, and confusion. He is found to have methemoglobinemia. What is the most appropriate treatment?

A. Activated charcoal
B. Methylene blue (Correct Answer)
C. Corticosteroids
D. High-flow oxygen

Explanation: ***Correct: Methylene blue*** - **Methylene blue** acts as an electron acceptor in the presence of NADPH, reducing the ferric iron (Fe3+) in **methemoglobin** back to ferrous iron (Fe2+), thus reversing methemoglobinemia. - It is the **first-line treatment** for symptomatic methemoglobinemia, especially in patients with low oxygen saturation and signs of end-organ hypoxia. - Typical dose: **1-2 mg/kg IV over 5 minutes**, with improvement expected within 30-60 minutes. *Incorrect: Activated charcoal* - **Activated charcoal** is used for gastrointestinal decontamination in cases of oral poisoning by adsorbing toxins. - It does not directly treat **methemoglobinemia** or reverse the effects of toxins already absorbed into the bloodstream. *Incorrect: Corticosteroids* - **Corticosteroids** possess anti-inflammatory and immunosuppressive properties. - They are used in conditions like asthma or autoimmune disorders and have no role in the direct treatment of **methemoglobinemia**. *Incorrect: High-flow oxygen* - While oxygen delivery should be maintained, **high-flow oxygen** alone is ineffective in treating significant **methemoglobinemia**. - This is because **methemoglobin** cannot bind oxygen effectively, regardless of the partial pressure of inspired oxygen, making direct reversal with methylene blue necessary.

Question 8: Persons with heterozygous sickle cell trait are protected from infection by:

A. Pneumococcus
B. P. falciparum (Correct Answer)
C. P. vivax
D. Salmonella

Explanation: ***P. falciparum*** - Individuals with heterozygous sickle cell trait have a **protective effect** against severe malaria caused by *P. falciparum* due to altered red blood cell morphology [1][2]. - The sickle hemoglobin (HbAS) provides a **selective advantage**, reducing the severity of malaria infections and the parasitic load [2][3]. *P. vivax* - Sickle cell trait does not confer significant protection against *P. vivax*, which primarily infects non-sickled red blood cells [2]. - The infection still occurs in individuals with the trait because it specifically affects the reticulocyte count, which is less impacted by sickling. *Salmonella* - While sickle cell disease is linked with increased susceptibility to **Salmonella infections**, the sickle cell trait itself does not provide protection against it [2]. - The trait does not influence immunity or susceptibility to bacterial pathogens like *Salmonella*. *Pneumococcus* - Individuals with sickle cell trait still have a normal risk of **invasive pneumococcal disease**, similar to those without the trait [2]. - Protection against *Pneumococcus* primarily relates to vaccination status and not to hemoglobinopathies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 598-599. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 50-51.

Question 9: All of the following are true about glutathione, except:

A. It is co-factor of various enzymes
B. It converts hemoglobin to methemoglobin (Correct Answer)
C. It is a tripeptide
D. It conjugates xenobiotics

Explanation: ***It converts hemoglobin to methemoglobin*** - Glutathione is a **reducing agent** that helps protect hemoglobin from oxidation, thus **preventing** the formation of methemoglobin. - **Methemoglobin** occurs when the iron in hemoglobin is oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state, which is a process glutathione actively counters. *It is co-factor of various enzymes* - Glutathione serves as a crucial **co-factor** for several enzymes, including **glutathione peroxidase**, which plays a vital role in antioxidant defense. - It participates in various **detoxification reactions** and catalyzes the reduction of harmful reactive oxygen species. *It is a tripeptide* - Glutathione is indeed a **tripeptide** composed of three amino acids: **glutamate**, **cysteine**, and **glycine**. - Its unique structure enables its diverse biological functions, including its prominent role as an antioxidant. *It conjugates xenobiotics* - Glutathione plays a critical role in **detoxifying xenobiotics** (foreign compounds) by conjugating with them, making them more water-soluble and easier to excrete. - This process is mediated by **glutathione S-transferases**, which attach glutathione to various toxic compounds.

Question 10: In which type of hemoglobin are zeta 2 and gamma 2 chains present?

A. Gower I
B. Gower II
C. Portland (Correct Answer)
D. Fetal hemoglobin

Explanation: ***Portland*** - **Portland hemoglobin** is a primitive embryonic hemoglobin composed of **zeta (ζ) 2 and gamma (γ) 2 chains** (ζ2γ2). - It plays a role in early fetal oxygen transport, particularly in the yolk sac stage. *Gower I* - **Gower I hemoglobin** is another embryonic hemoglobin, but it consists of **zeta (ζ) 2 and epsilon (ε) 2 chains** (ζ2ε2). - This composition is crucial for oxygen delivery during the very initial stages of embryonic development. *Gower II* - **Gower II hemoglobin** is an embryonic hemoglobin made up of **alpha (α) 2 and epsilon (ε) 2 chains** (α2ε2). - It represents a transitional form as the embryo develops and starts producing alpha globin chains. *Fetal hemoglobin* - **Fetal hemoglobin (HbF)** consists of **alpha (α) 2 and gamma (γ) 2 chains** (α2γ2). - It is the predominant hemoglobin during the second and third trimesters of pregnancy and has a higher affinity for oxygen than adult hemoglobin.

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