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Question 1Blood Banking

Which ABO group is known as the universal donor for red cell concentrates?

  1. Group AB
  2. Group A
  3. Group B
  4. Group O Correct answer.

Explanation

Group O red cells lack A and B antigens, so recipients of any ABO group will not form an antigen-antibody reaction against them. This makes O red cell units suitable when the recipient's ABO type is unknown. Group AB plasma is the universal plasma donor, which is a separate concept.

Question 2Blood Banking

A donor's forward grouping shows agglutination with anti-A and anti-B reagents, while the reverse grouping shows no agglutination with A1 or B cells. Which is the most likely ABO discrepancy?

  1. An ABO typing error caused by a missing reverse reaction in an elderly patient Correct answer.
  2. A group AB individual with a normal reverse grouping
  3. A subgroup with weak A antigen expression
  4. A group O individual with extra A antigen acquired from a transfusion

Explanation

Group AB sera normally contain no anti-A or anti-B, so the reverse grouping should be negative and matches this pattern. However, the question asks for a discrepancy, and the classic cause of missing reverse antibodies is decreased antibody production in the elderly or in immunocompromised patients. The forward and reverse results here are actually concordant with group AB, so the discrepancy is the absence of expected antibodies in a person whose forward type is AB.

Question 3Blood Banking

Which antibody class is most commonly responsible for hemolytic disease of the fetus and newborn?

  1. IgM anti-A
  2. IgA anti-Lea
  3. IgG anti-D Correct answer.
  4. IgE anti-I

Explanation

IgG antibodies cross the placenta, and IgG anti-D directed against the RhD antigen is the classic cause of severe hemolytic disease of the fetus and newborn. IgM antibodies are too large to cross the placenta efficiently. ABO-related disease is usually milder and involves IgG anti-A or anti-B, not IgM.

Question 4Blood Banking

A unit of red cells is issued for a patient with a negative antibody screen. What is the minimum pretransfusion testing required before issue?

  1. ABO and RhD typing plus an immediate spin crossmatch only
  2. ABO typing only, since the antibody screen is negative
  3. ABO and RhD typing of the donor unit only
  4. ABO and RhD typing of the patient and a crossmatch with the donor unit Correct answer.

Explanation

Pretransfusion testing requires the patient's ABO and RhD type, an antibody screen, and a crossmatch or computer crossmatch against the specific unit. A negative antibody screen does not eliminate the need for compatibility testing. The crossmatch confirms donor-recipient compatibility at the serologic level.

Question 5Blood Banking

Which storage temperature range is standard for liquid red blood cell concentrates?

  1. -18 to -25 degrees Celsius
  2. 20 to 24 degrees Celsius
  3. 37 degrees Celsius
  4. 1 to 6 degrees Celsius Correct answer.

Explanation

Red cell concentrates are stored at 1 to 6 degrees Celsius to slow metabolic activity while maintaining cell viability. Refrigeration also limits bacterial proliferation in the unit. Frozen storage at very low temperatures is used for rare units with glycerol cryoprotection.

Question 6Blood Banking

A patient's serum reacts with all panel cells at the indirect antiglobulin phase, and the autocontrol is also positive. Which explanation is most likely?

  1. A cold agglutinin of the IgM class
  2. A warm autoantibody Correct answer.
  3. An anti-Kell antibody
  4. An anti-Leb antibody

Explanation

A positive autocontrol together with panreactivity at the antiglobulin phase suggests a warm autoantibody directed against a high-incidence antigen on the patient's own cells. Warm autoantibodies typically react at 37 degrees Celsius and at the IAT phase. Further testing with adsorption techniques is needed to identify any underlying alloantibody.

Question 7Blood Banking

Which component is the preferred product for a patient with severe thrombocytopenia who requires a rapid platelet count increase?

  1. Packed red cells
  2. Fresh frozen plasma
  3. Cryoprecipitate
  4. Platelet concentrate Correct answer.

Explanation

Platelet concentrates provide a concentrated dose of platelets and are the standard product for correcting severe thrombocytopenia. Each unit typically raises the platelet count by a predictable increment in an average adult. Plasma and cryoprecipitate do not contain sufficient viable platelets to correct thrombocytopenia.

Question 8Blood Banking

What is the main purpose of leukoreduction of blood components?

  1. To extend the shelf life of red cells beyond 42 days
  2. To increase the oxygen-carrying capacity of red cells
  3. To reduce febrile nonhemolytic transfusion reactions and cytomegalovirus transmission Correct answer.
  4. To prevent ABO incompatibility reactions

Explanation

Leukoreduction removes white blood cells, which reduces the incidence of febrile nonhemolytic transfusion reactions and lowers the risk of transmitting cell-associated viruses such as cytomegalovirus. It also reduces HLA alloimmunization in multiply transfused patients. Leukoreduction does not change the ABO compatibility of the unit or extend storage beyond the licensed period.

Question 9Blood Banking

Which test is used to detect fetomaternal hemorrhage in a RhD-negative mother after delivery of an RhD-positive infant?

  1. Direct antiglobulin test
  2. Coombs crossmatch
  3. Antibody titration
  4. Kleihauer-Betke acid elution test Correct answer.

Explanation

The Kleihauer-Betke test uses acid elution to identify fetal hemoglobin-containing cells in the maternal circulation. The percentage of fetal cells is used to calculate the dose of Rh immune globulin needed. Flow cytometry is an alternative method for quantifying fetomaternal hemorrhage.

Question 10Blood Banking

Which of the following best describes the principle of the indirect antiglobulin test?

  1. It detects antibodies already bound to the patient's red cells in vivo.
  2. It detects ABO antigens on the donor's red cells directly.
  3. It detects antibodies that bind red cells in vitro and are then detected with anti-human globulin. Correct answer.
  4. It measures complement levels in the patient's serum.

Explanation

The indirect antiglobulin test incubates patient serum with reagent red cells so that antibodies in the serum can bind in vitro. After washing, anti-human globulin is added to bridge antibody-coated cells and produce agglutination. The direct antiglobulin test, by contrast, detects antibody already bound to circulating red cells in vivo.

Question 11Blood Banking

A unit of red cells is returned to the blood bank after being out of controlled storage for 40 minutes. What is the appropriate action?

  1. Discard the unit because the allowed out-of-storage time has been exceeded Correct answer.
  2. Store the unit at room temperature for later use
  3. Return the unit to inventory because it was out for less than 30 minutes only
  4. Transfuse the unit immediately without documentation

Explanation

Red cell units that are out of controlled storage for more than 30 minutes are generally considered unsuitable for return to inventory because of the risk of bacterial growth and loss of viability. The unit should be discarded according to institutional policy. Documentation of the excursion is also required.

Question 12Blood Banking

Which antigen system is most important to consider, after ABO, when selecting red cells for a patient with sickle cell disease on a chronic transfusion program?

  1. I system
  2. Rh system, including partial and variant antigens Correct answer.
  3. Lewis system
  4. P system

Explanation

Patients with sickle cell disease are at high risk of alloimmunization to Rh antigens, especially variant and partial Rh antigens such as partial C and e. Extended matching for Rh and Kell antigens is often used in chronic transfusion programs. Lewis, P, and I antibodies are generally clinically insignificant or transient.

Question 13Blood Banking

What is the recommended storage temperature for fresh frozen plasma?

  1. 1 to 6 degrees Celsius
  2. -18 degrees Celsius or colder Correct answer.
  3. 37 degrees Celsius
  4. 20 to 24 degrees Celsius

Explanation

Fresh frozen plasma must be stored at -18 degrees Celsius or colder to preserve labile clotting factors such as factor V and factor VIII. Once thawed, it should be used promptly or stored at 1 to 6 degrees Celsius for a limited period. Storage at warmer temperatures leads to loss of factor activity.

Question 14Blood Banking

A patient with a history of anaphylactic reaction to a blood transfusion is found to be IgA deficient with anti-IgA antibodies. Which product should be selected for future transfusions?

  1. Whole blood from a random donor
  2. IgA-deficient plasma and washed red cells Correct answer.
  3. Cryoprecipitate prepared from pooled plasma
  4. Platelets stored in plasma

Explanation

Patients with IgA deficiency and anti-IgA antibodies can experience severe anaphylactic reactions to plasma-containing products. They should receive IgA-deficient plasma and washed red cells to remove residual plasma. Cellular components should be washed to minimize plasma exposure.

Question 15Blood Banking

Which of the following is a characteristic of anti-D formed after RhD-positive blood is given to an RhD-negative person?

  1. It is usually IgM and reacts only at room temperature
  2. It is directed against the Lewis antigen system
  3. It is usually IgG and can cause hemolytic transfusion reactions and HDFN Correct answer.
  4. It is a naturally occurring antibody present from birth

Explanation

Anti-D is typically an IgG antibody produced after exposure to RhD-positive red cells through transfusion or pregnancy. IgG anti-D can cause delayed hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. It is not naturally occurring and is not directed against Lewis antigens.

Question 16Blood Banking

Which method is considered the reference method for ABO typing in a patient with a history of recent massive transfusion?

  1. Performing a direct antiglobulin test only
  2. Relying on the posttransfusion forward grouping only
  3. Testing a pretransfusion sample and comparing forward and reverse grouping Correct answer.
  4. Testing the donor units instead of the patient

Explanation

Massive transfusion can dilute the patient's own red cells and antibodies, making posttransfusion typing unreliable. A pretransfusion sample provides the most accurate ABO and RhD type. Comparison of forward and reverse grouping also helps detect discrepancies.

Question 17Blood Banking

What is the primary purpose of adding a preservative solution such as AS-1 to a red cell unit?

  1. To increase the hematocrit of the unit
  2. To extend red cell storage to 42 days by supporting metabolism Correct answer.
  3. To sterilize the unit before storage
  4. To prevent graft-versus-host disease

Explanation

Additive solutions such as AS-1 provide nutrients and maintain pH to support red cell metabolism during storage, extending the shelf life to 42 days. They also allow more plasma to be removed from the unit. They do not sterilize the unit or prevent graft-versus-host disease.

Question 18Blood Banking

Which antibody is most likely to be detected in a patient who has received multiple units of red cells and shows a positive antibody screen with a positive autocontrol that disappears after adsorption?

  1. A naturally occurring anti-A
  2. An alloantibody masked by a warm autoantibody Correct answer.
  3. An anti-M antibody
  4. A cold agglutinin of the IgM class

Explanation

A warm autoantibody can mask the presence of an underlying alloantibody by coating all panel cells and causing panreactivity. Adsorption techniques remove the autoantibody from the serum so that any remaining alloantibody can be identified. This is a common challenge in multiply transfused patients.

Question 19Blood Banking

What is the maximum allowable storage period for platelets stored at 20 to 24 degrees Celsius with agitation?

  1. 42 days
  2. 24 hours
  3. 14 days
  4. 5 to 7 days Correct answer.

Explanation

Platelets are stored at 20 to 24 degrees Celsius with continuous agitation to maintain viability and function. The maximum storage period is typically 5 to 7 days, depending on the collection and testing method. Bacterial contamination risk limits longer storage.

Question 20Blood Banking

A patient is group A, RhD-negative, and has anti-D. Which red cell units are compatible?

  1. Group A, RhD-positive units
  2. Group AB, RhD-positive units
  3. Group O, RhD-positive units
  4. Group A, RhD-negative units Correct answer.

Explanation

The patient has anti-D, so any RhD-positive unit would be incompatible regardless of ABO type. Group A, RhD-negative units match both the patient's ABO group and RhD status. Group O, RhD-negative units would also be acceptable, but the option lists RhD-positive units.

Question 21Blood Banking

Which condition is a classic indication for therapeutic plasma exchange rather than simple plasma transfusion?

  1. Factor VIII deficiency
  2. Hypofibrinogenemia
  3. Thrombotic thrombocytopenic purpura Correct answer.
  4. Vitamin K deficiency bleeding

Explanation

Thrombotic thrombocytopenic purpura is treated with therapeutic plasma exchange to remove abnormal von Willebrand factor multimers and replace deficient ADAMTS13. Simple plasma transfusion does not achieve the same effect. Factor deficiencies and hypofibrinogenemia are managed with factor concentrates or cryoprecipitate.

Question 22Blood Banking

Which of the following is the most appropriate action when a donor reports a history of hepatitis B infection?

  1. Permanently defer the donor from donation Correct answer.
  2. Accept the donor for plasma donation only
  3. Accept the donor after a negative HBsAg test
  4. Accept the donor if liver enzymes are normal

Explanation

A history of hepatitis B infection is generally a basis for permanent deferral because of the risk of transmitting the virus through transfusion. Normal liver enzymes or a single negative test do not eliminate the risk. Donor screening criteria are designed to protect recipients.

Question 23Blood Banking

Which of the following best describes the role of the direct antiglobulin test in a delayed hemolytic transfusion reaction?

  1. It measures the hemoglobin level in the patient
  2. It detects antibody or complement coating the patient's red cells after transfusion Correct answer.
  3. It confirms the ABO type of the donor unit
  4. It identifies the donor unit that caused the reaction

Explanation

The direct antiglobulin test detects antibody or complement bound to the patient's circulating red cells, which is a hallmark of immune hemolysis after transfusion. A positive result supports the diagnosis of a delayed hemolytic reaction. It does not identify the specific donor unit or measure hemoglobin.

Question 24Blood Banking

Which of the following is a key advantage of using a computer crossmatch instead of a serologic crossmatch?

  1. It allows transfusion of ABO-incompatible units
  2. It removes the need for an antibody screen
  3. It avoids the need for a serologic crossmatch when validated criteria are met Correct answer.
  4. It eliminates the need for ABO typing of the patient

Explanation

A computer crossmatch can replace the serologic crossmatch when the patient has a valid ABO and RhD type on file, a negative antibody screen, and no history of clinically significant antibodies. The system must be validated to detect ABO incompatibility. It does not eliminate ABO typing or antibody screening.

Question 25Blood Banking

A patient's serum contains anti-Jka. Which of the following statements about this antibody is correct?

  1. It is a clinically significant antibody that can cause delayed hemolytic transfusion reactions Correct answer.
  2. It is directed against the ABO antigen system
  3. It is a naturally occurring IgM antibody of no clinical significance
  4. It reacts only at room temperature and never at 37 degrees Celsius

Explanation

Anti-Jka is directed against the Kidd antigen system and is a clinically significant antibody capable of causing delayed hemolytic transfusion reactions. It may show variable reactivity and can fall to undetectable levels over time. Patients with a history of anti-Jka should receive antigen-negative units.

Question 26Clinical Chemistry

A serum sample is described as icteric. Which analyte is most likely to be falsely decreased by this interference on a wet-chemistry analyzer?

  1. Glucose by hexokinase Correct answer.
  2. Creatinine by picrate reaction
  3. Total protein by biuret
  4. Cholesterol by enzymatic endpoint

Explanation

Bilirubin absorbs strongly near 340 nm and can interfere with NADH/NADPH-based absorbance readings, which is how hexokinase glucose methods are measured. The other listed methods read at longer wavelengths (biuret around 540 nm, picrate around 500 nm, Trinder-type cholesterol around 500 nm) where bilirubin interference is much smaller.

Question 27Clinical Chemistry

Which specimen type is preferred for measuring ionized calcium in a patient with suspected hyperparathyroidism?

  1. 24-hour urine collected with acid preservative
  2. Heparinized whole blood analyzed anaerobically Correct answer.
  3. Plasma collected in EDTA
  4. Serum collected in a plain red-top tube

Explanation

Ionized calcium must be measured on anaerobically handled whole blood anticoagulated with balanced heparin, because exposure to air raises pH and lowers ionized calcium. EDTA chelates calcium and plain serum loses the ionized fraction during clotting.

Question 28Clinical Chemistry

A patient's fasting glucose is 5.4 mmol/L and HbA1c is 6.9%. Which interpretation best fits the current WHO diagnostic framework?

  1. Diabetes based on HbA1c alone Correct answer.
  2. Normal glucose tolerance with no further action
  3. Prediabetes based on HbA1c alone
  4. Impaired fasting glucose with a normal HbA1c

Explanation

An HbA1c of 6.5% or higher meets the diagnostic threshold for diabetes, even when fasting glucose is below 7.0 mmol/L. Because the two tests are discordant, the result should be confirmed on a second sample, but the HbA1c value itself is diagnostic.

Question 29Clinical Chemistry

Which calculation correctly expresses the anion gap from a chemistry panel?

  1. Chloride plus bicarbonate minus sodium
  2. Sodium minus chloride minus potassium
  3. Sodium minus (chloride plus bicarbonate) Correct answer.
  4. Sodium plus potassium minus chloride

Explanation

The anion gap is the difference between the measured cation sodium and the measured anions chloride and bicarbonate. Potassium is often omitted because its concentration is small and relatively stable.

Question 30Clinical Chemistry

A patient with severe vomiting presents with a pH of 7.52, PCO2 of 48 mmHg, and bicarbonate of 38 mmol/L. How is this acid-base disturbance best classified?

  1. Acute respiratory acidosis without compensation
  2. Mixed respiratory and metabolic acidosis
  3. Respiratory alkalosis with metabolic compensation
  4. Metabolic alkalosis with respiratory compensation Correct answer.

Explanation

A raised pH with elevated bicarbonate indicates a primary metabolic alkalosis, and the elevated PCO2 reflects hypoventilation as respiratory compensation. Loss of gastric acid during vomiting is the classic cause.

Question 31Clinical Chemistry

Which enzyme is considered the most liver-specific marker of cholestasis when markedly elevated?

  1. Alanine aminotransferase
  2. Aspartate aminotransferase
  3. Lactate dehydrogenase
  4. Alkaline phosphatase Correct answer.

Explanation

Alkaline phosphatase rises predominantly when bile flow is obstructed, and a marked isolated elevation suggests cholestasis. Aminotransferases reflect hepatocellular injury, while LDH is widely distributed and nonspecific.

Question 32Clinical Chemistry

A patient with nephrotic-range proteinuria has a serum albumin of 19 g/L. Which additional finding is most consistent with this condition?

  1. Low LDL cholesterol
  2. Polycythemia with low triglycerides
  3. Hyperlipidemia with elevated LDL cholesterol Correct answer.
  4. Elevated serum creatinine with normal lipids

Explanation

Nephrotic syndrome causes hepatic synthesis of lipoproteins in response to hypoalbuminemia, producing hyperlipidemia. The loss of albumin and the compensatory hepatic response explain the elevated cholesterol.

Question 33Clinical Chemistry

Which statement about the enzymatic creatinine assay is correct?

  1. It requires a strong acid precipitation step before reading.
  2. It requires alkaline picrate and is prone to ketoacid interference.
  3. It measures creatinine by ultraviolet absorbance at 340 nm without enzymes.
  4. It uses creatinine iminohydrolase and is less affected by ketoacids. Correct answer.

Explanation

Enzymatic creatinine methods use creatinine iminohydrolase or creatininase and are more specific than the Jaffe reaction. They avoid the ketoacid and protein interference that complicates alkaline picrate assays.

Question 34Clinical Chemistry

Which cardiac marker remains elevated the longest after an acute myocardial infarction, making it useful for late presentation?

  1. Creatine kinase MB
  2. Myoglobin
  3. Troponin I Correct answer.
  4. Aspartate aminotransferase

Explanation

Cardiac troponin I and T stay elevated for roughly 7 to 14 days after infarction, which makes them useful for patients presenting late. Myoglobin and CK-MB return to baseline much sooner.

Question 35Clinical Chemistry

A patient's TSH is elevated and free T4 is low. Which pattern does this represent?

  1. Primary hypothyroidism Correct answer.
  2. Primary hyperthyroidism
  3. Central hyperthyroidism
  4. Subclinical hyperthyroidism

Explanation

A high TSH with a low free T4 indicates the thyroid gland is failing to produce hormone, so pituitary stimulation increases. This is the classic pattern of primary hypothyroidism.

Question 36Clinical Chemistry

Which laboratory finding is most characteristic of primary hyperaldosteronism?

  1. Hypokalemia with elevated renin
  2. Hypokalemia with suppressed plasma renin activity Correct answer.
  3. Hyperkalemia with suppressed aldosterone
  4. Hyperkalemia with elevated renin

Explanation

Autonomous aldosterone production causes sodium retention and potassium wasting, and the resulting volume expansion suppresses renin. The combination of high aldosterone and low renin is the diagnostic hallmark.

Question 37Clinical Chemistry

A 24-hour urine collection for cortisol is being validated. Which measurement is most appropriate for confirming adequate collection?

  1. Urine glucose
  2. Urine creatinine excretion Correct answer.
  3. Urine specific gravity
  4. Urine pH

Explanation

Creatinine excretion is relatively constant per day, so measuring total urine creatinine confirms that the collection is complete. Specific gravity, pH, and glucose do not reliably indicate collection completeness.

Question 38Clinical Chemistry

Which statement about a competitive immunoassay for a small molecule such as free T4 is correct?

  1. The signal decreases as analyte concentration increases. Correct answer.
  2. The assay cannot use a labeled antigen.
  3. The signal increases as analyte concentration increases.
  4. The assay requires two capture antibodies in a sandwich format.

Explanation

In a competitive immunoassay, labeled and unlabeled analyte compete for a limited number of binding sites, so more analyte displaces more label and lowers the signal. Sandwich formats are used for large molecules with multiple epitopes, not small haptens.

Question 39Clinical Chemistry

A serum sample shows a sodium of 121 mmol/L on indirect ion-selective electrode but 139 mmol/L on direct ion-selective electrode. What is the most likely cause?

  1. Improper electrode calibration with a high standard
  2. True hyponatremia requiring saline
  3. Sample contamination with potassium EDTA
  4. Pseudohyponatremia from severe hyperproteinemia Correct answer.

Explanation

Indirect ion-selective electrodes measure sodium in the plasma water fraction after dilution, so a very high protein or lipid content lowers the reported result. Direct electrodes measure activity in undiluted whole sample and are unaffected, which reveals pseudohyponatremia.

Question 40Clinical Chemistry

Which trace element deficiency is associated with cardiomyopathy that responds to selenium supplementation?

  1. Selenium Correct answer.
  2. Chromium
  3. Zinc
  4. Copper

Explanation

Selenium is a cofactor for glutathione peroxidase, and deficiency has been linked to Keshan disease, a cardiomyopathy that improves with supplementation. Zinc, copper, and chromium deficiencies produce different clinical pictures.

Question 41Clinical Chemistry

Which laboratory result pattern best supports a diagnosis of SIADH?

  1. Low serum osmolality with high urine osmolality and euvolemia Correct answer.
  2. Low serum osmolality with low urine osmolality
  3. High serum sodium with high urine sodium
  4. High serum osmolality with low urine osmolality

Explanation

SIADH produces dilutional hyponatremia with inappropriately concentrated urine and clinical euvolemia. The urine osmolality exceeds the serum osmolality because ADH is inappropriately high.

Question 42Clinical Chemistry

Which specimen collection requirement applies to a plasma ammonia measurement?

  1. Collect in EDTA or heparin, place on ice, and analyze promptly. Correct answer.
  2. Collect in a plain tube and transport at room temperature.
  3. Collect in a fluoride tube and store overnight at 4 degrees Celsius.
  4. Collect in a serum separator tube and centrifuge after 2 hours.

Explanation

Ammonia rises artifactually in whole blood as red cells and platelets release it, so samples must be kept cold and separated quickly. EDTA or heparin tubes are appropriate, and prompt analysis limits preanalytical error.

Question 43Clinical Chemistry

A patient with a suspected paraprotein has a total protein of 95 g/L by biuret and an albumin of 30 g/L. Which additional test best characterizes the paraprotein?

  1. Prothrombin time
  2. Serum protein electrophoresis with immunofixation Correct answer.
  3. Serum amylase
  4. Urine pH

Explanation

Serum protein electrophoresis separates the globulin fractions, and immunofixation identifies the heavy and light chains of a monoclonal band. The globulin gap of 65 g/L suggests a substantial paraprotein that requires this characterization.

Question 44Clinical Chemistry

Which is the most appropriate sample for measuring sweat chloride in a suspected cystic fibrosis case?

  1. Two separate sweat samples collected on different days Correct answer.
  2. A saliva chloride measurement
  3. A single random sweat sample collected after exercise
  4. A serum chloride measurement

Explanation

Sweat chloride testing requires adequate sweat volume and, for a positive result, confirmation on a second sample. Serum and saliva chloride do not reflect the sweat gland defect in cystic fibrosis.

Question 45Clinical Chemistry

Which calculation gives the serum osmolality estimated from measured sodium, glucose, and urea?

  1. Sodium plus glucose plus urea, all in mmol/L
  2. 2 times sodium plus glucose plus urea, all in mmol/L Correct answer.
  3. 2 times sodium minus glucose minus urea
  4. Sodium divided by glucose plus urea

Explanation

The estimated osmolality is twice the sodium concentration plus glucose and urea, each in mmol/L. The multiplier of two accounts for the accompanying anions of sodium.

Question 46Clinical Chemistry

A patient's measured osmolality exceeds the calculated osmolality by 25 mOsm/kg. Which cause best explains this osmolal gap?

  1. Methanol ingestion Correct answer.
  2. Elevated glucose
  3. Hypernatremia
  4. Elevated urea

Explanation

An osmolal gap indicates unmeasured osmotically active solutes, and toxic alcohols such as methanol are classic causes. Urea, glucose, and sodium are already included in the calculated formula and therefore do not create a gap.

Question 47Clinical Chemistry

Which factor most strongly affects the reference interval for alkaline phosphatase in a healthy population?

  1. Blood group ABO type
  2. Age and skeletal growth status Correct answer.
  3. Serum sodium concentration
  4. Dietary fat intake on the day of collection

Explanation

Alkaline phosphatase is derived from bone as well as liver, so growing children and adolescents have markedly higher values than adults. Age-specific reference intervals are therefore essential for correct interpretation.

Question 48Clinical Chemistry

A laboratory reports a creatinine result of 900 micromol/L in a sample with a very high bilirubin. Which approach best addresses the interference in the Jaffe method?

  1. Adding EDTA to the reaction
  2. Increasing the sample volume
  3. Reading the absorbance at 340 nm
  4. Rate-blanking with an alkaline picrate kinetic reading Correct answer.

Explanation

Kinetic Jaffe methods use rate-blanking to subtract the rapid nonspecific reaction of interfering substances such as bilirubin. This improves specificity without altering the sample volume or wavelength.

Question 49Clinical Chemistry

Which statement about point-of-care blood gas analyzers measuring sodium is correct?

  1. They use direct ion-selective electrodes and report activity in whole blood. Correct answer.
  2. They use indirect electrodes after a fixed dilution.
  3. They require serum separation before measurement.
  4. They measure sodium by flame emission photometry.

Explanation

Blood gas analyzers use direct ion-selective electrodes on whole blood, so they report sodium activity without dilution. This is why they are less affected by hyperproteinemia than indirect methods.

Question 50Clinical Chemistry

Which is the correct interpretation of a urine albumin-to-creatinine ratio of 45 mg/mmol in a patient with diabetes?

  1. Normal albumin excretion
  2. Severely increased albuminuria requiring dialysis
  3. Moderately increased albuminuria consistent with early diabetic kidney disease Correct answer.
  4. Invalid because urine creatinine was not measured

Explanation

An albumin-to-creatinine ratio between 3 and 30 mg/mmol is moderately increased, and values above 30 mg/mmol indicate severely increased albuminuria in many guidelines. A value of 45 mg/mmol therefore indicates significant albuminuria consistent with diabetic kidney disease.