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Question 1Blood Banking / Immunohematology

A patient's serum reacts with reagent A1 cells but not with reagent B cells at immediate spin. Which ABO forward typing result is expected to agree with this reverse pattern?

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

Explanation

Anti-A in the serum with no anti-B indicates the patient is group B, since group B individuals form anti-A and their red cells carry the B antigen. A reverse pattern reacting only with A1 cells therefore matches a forward type of group B.

Question 2Blood Banking / Immunohematology

Which immunoglobulin class is the predominant form of naturally occurring ABO antibodies in adult serum?

  1. IgG
  2. IgA
  3. IgE
  4. IgM Correct answer.

Explanation

ABO antibodies are predominantly IgM, which is why they typically react at immediate spin or room temperature and can activate complement efficiently. IgG anti-A and anti-B may also be present, but IgM is the main class.

Question 3Blood Banking / Immunohematology

A tube containing a red cell suspension is centrifuged and the cell button is resuspended by gentle tilting. The technologist observes agglutinates that remain intact after further shaking. What does this indicate?

  1. Hemolysis
  2. True agglutination Correct answer.
  3. Rouleaux
  4. A negative reaction

Explanation

True agglutination produces stable clumps that persist after the button is broken up and the tube is shaken. Rouleaux, by contrast, disperses readily with saline dilution or vigorous shaking.

Question 4Blood Banking / Immunohematology

Which reagent is used to perform the immediate spin phase of a crossmatch in a tube method?

  1. Polyethylene glycol
  2. Saline Correct answer.
  3. Anti-human globulin
  4. LISS additive

Explanation

The immediate spin phase is performed in saline to detect IgM antibodies that react at room temperature. Anti-human globulin is added later for the antiglobulin phase.

Question 5Blood Banking / Immunohematology

Which antigen system is responsible for the majority of severe hemolytic disease of the fetus and newborn?

  1. Rh (D) Correct answer.
  2. Kell
  3. Duffy
  4. Lewis

Explanation

Anti-D is the most common cause of severe hemolytic disease of the fetus and newborn, which is why Rh immune globulin prophylaxis is given to Rh-negative mothers. Other systems such as Kell can cause severe disease but are less frequent.

Question 6Blood Banking / Immunohematology

A donor unit is labeled group O. Which ABO red cell antigens are present on these donor red cells?

  1. Neither A nor B antigen Correct answer.
  2. B antigen only
  3. Both A and B antigens
  4. A antigen only

Explanation

Group O red cells lack both A and B antigens, and the plasma contains both anti-A and anti-B. This is why group O red cells can be given to recipients of any ABO group in urgent situations.

Question 7Blood Banking / Immunohematology

What is the primary purpose of performing a direct antiglobulin test (DAT) on a patient's red cells?

  1. To detect antibody or complement coating the patient's red cells in vivo Correct answer.
  2. To detect unexpected antibodies in the patient's serum
  3. To confirm the patient's ABO group
  4. To measure the patient's hemoglobin concentration

Explanation

The DAT uses anti-human globulin to detect immunoglobulin or complement already bound to red cells in the circulation. The indirect antiglobulin test, by contrast, detects antibody in the serum.

Question 8Blood Banking / Immunohematology

Which of the following is the correct storage temperature range for red blood cell units in a blood bank refrigerator?

  1. 10 to 15 degrees Celsius
  2. 20 to 24 degrees Celsius
  3. Minus 18 to minus 25 degrees Celsius
  4. 1 to 6 degrees Celsius Correct answer.

Explanation

Red blood cell units are stored at 1 to 6 degrees Celsius to maintain viability and limit bacterial growth. Warmer temperatures risk bacterial proliferation, and freezing requires a cryoprotectant.

Question 9Blood Banking / Immunohematology

A patient is group A and has a positive antibody screen. The antibody identification panel shows reactivity with all cells except those lacking the Kell antigen. Which antibody is most likely present?

  1. Anti-Jka
  2. Anti-K Correct answer.
  3. Anti-Fya
  4. Anti-S

Explanation

Reactivity with all cells except Kell-negative cells indicates anti-K, which is directed against the Kell antigen. The pattern of reactivity matching a single antigen's presence identifies the specificity.

Question 10Blood Banking / Immunohematology

A patient with a history of multiple transfusions has an antibody that reacts only with enzyme-treated cells and shows dosage. Which antibody is most likely?

  1. Anti-Jka Correct answer.
  2. Anti-K
  3. Anti-M
  4. Anti-D

Explanation

Anti-Jka is a common clinically significant antibody that often shows dosage and enhanced reactivity with enzyme-treated cells. Anti-M is usually enzyme-sensitive and anti-D is not typically dosage-dependent.

Question 11Blood Banking / Immunohematology

A patient's serum reacts with group O cells but not with group A1 or B cells in the reverse typing. Which situation best explains this finding?

  1. The patient is group O with weak anti-A and anti-B
  2. The patient has an alloantibody to a high-incidence antigen
  3. The patient is group AB
  4. The patient is a subgroup of A with anti-A1 Correct answer.

Explanation

An A subgroup such as A2 or A2B may produce anti-A1 that reacts with A1 cells but not with group O cells; the finding of reactivity with O cells is unusual, but the classic subgroup pattern involves anti-A1. The presence of anti-A1 in a subgroup of A explains reactivity with A1 cells while B cells remain nonreactive.

Question 12Blood Banking / Immunohematology

Which phenomenon is caused by the presence of anti-A1 in the serum of an A2 individual?

  1. A positive antibody screen with O cells only
  2. A positive antibody screen with B cells only
  3. A negative antibody screen with all cells
  4. A positive antibody screen with A1 cells only Correct answer.

Explanation

Anti-A1 reacts with A1 cells but not with A2 or O cells, so it produces a positive screen only when A1 cells are included in the panel. This is a common cause of an ABO discrepancy in A subgroups.

Question 13Blood Banking / Immunohematology

A DAT is performed on a newborn's cord blood and is positive. Which antibody is most likely responsible if the mother is Rh-negative and the infant is Rh-positive?

  1. IgE anti-K
  2. IgM anti-A
  3. IgA anti-B
  4. IgG anti-D Correct answer.

Explanation

IgG anti-D crosses the placenta and coats fetal Rh-positive red cells, producing a positive DAT and hemolytic disease. IgM antibodies do not cross the placenta and would not coat fetal cells.

Question 14Blood Banking / Immunohematology

A patient's antibody screen is positive, and the panel shows reactivity with cells positive for C, e, and K. Which additional testing would best help determine the antibody specificity?

  1. Repeat the screen with the same panel
  2. Perform an ABO reverse typing
  3. Perform a direct antiglobulin test
  4. Test selected cells that separate the antigens Correct answer.

Explanation

When several antigens travel together on the panel, testing cells that separate the antigens allows the specific antibody to be identified. Repeating the same panel or performing a DAT does not resolve the specificity.

Question 15Blood Banking / Immunohematology

A patient with cold agglutinin disease has a positive DAT. Which reagent is most likely to give a positive reaction in the DAT?

  1. Anti-IgG only
  2. Anti-C3d only Correct answer.
  3. Anti-IgE only
  4. Anti-IgA only

Explanation

Cold agglutinins are IgM antibodies that fix complement, so the DAT is typically positive with anti-C3d and negative with anti-IgG. The IgM dissociates during washing, leaving complement on the cells.

Question 16Blood Banking / Immunohematology

A patient is group O and requires a transfusion. Which ABO group of plasma is most appropriate to avoid hemolysis of the patient's red cells?

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

Explanation

Group O recipients should receive group AB plasma because it contains no anti-A or anti-B that could hemolyze the recipient's cells. Group A or B plasma contains antibodies against the recipient's ABO antigens.

Question 17Blood Banking / Immunohematology

Which of the following is the most important reason to perform an immediate spin crossmatch in a patient with a negative antibody screen?

  1. To detect anti-Jka
  2. To detect ABO incompatibility Correct answer.
  3. To detect anti-Fya
  4. To detect anti-D

Explanation

The immediate spin crossmatch primarily detects ABO incompatibility between donor and recipient. Antibodies such as anti-D, anti-Jka, and anti-Fya are detected in the antiglobulin phase or antibody screen.

Question 18Blood Banking / Immunohematology

A patient's serum contains anti-K. Which red cell unit would be most appropriate for transfusion?

  1. Any group O unit
  2. K-positive, crossmatch-compatible unit
  3. Any unit with a negative antibody screen
  4. K-negative, crossmatch-compatible unit Correct answer.

Explanation

A patient with anti-K should receive K-negative red cells that are also crossmatch-compatible to prevent a hemolytic transfusion reaction. A K-positive unit could trigger an anamnestic or immediate reaction.

Question 19Blood Banking / Immunohematology

Which of the following best describes the principle of the gel column agglutination technique?

  1. Antigen is detected by enzyme-linked immunosorbent assay
  2. Antibody is detected by complement fixation in a fluid phase
  3. Red cells are separated by density through a gel matrix; agglutinated cells remain at the top Correct answer.
  4. Red cells are lysed and hemoglobin is measured spectrophotometrically

Explanation

In gel testing, agglutinated red cells are trapped in the gel matrix while unagglutinated cells pass through to the bottom. The position of the cells indicates the strength of the reaction.

Question 20Blood Banking / Immunohematology

A patient is group A2B with unexpected reactivity against A1 cells, but not A2 cells, during reverse ABO grouping. Which antibody is most likely responsible?

  1. Anti-B
  2. Anti-D
  3. Anti-K
  4. Anti-A1 Correct answer.

Explanation

A2B individuals may produce anti-A1, causing unexpected reactivity with A1 cells but not A2 cells in reverse ABO grouping. Routine unexpected-antibody screens use group O reagent cells, so anti-A1 would not explain a positive routine screen.

Question 21Blood Banking / Immunohematology

Which of the following is the most appropriate action when a patient's serum reacts with all panel cells, including autocontrol, in the antiglobulin phase?

  1. Perform additional testing to evaluate for autoantibody or alloantibody Correct answer.
  2. Report the antibody as anti-D
  3. Transfuse group O red cells without further testing
  4. Repeat the ABO typing only

Explanation

Panreactivity with a positive autocontrol suggests an autoantibody or a high-incidence alloantibody, and additional testing such as adsorption or elution is needed. Reporting a specific antibody or transfusing without further evaluation is unsafe.

Question 22Blood Banking / Immunohematology

A patient has a positive DAT with anti-IgG and a history of recent transfusion. Which explanation is most consistent with these findings?

  1. Cold agglutinin disease
  2. An immediate spin incompatibility
  3. A delayed hemolytic transfusion reaction Correct answer.
  4. A clerical error in ABO typing

Explanation

A delayed hemolytic transfusion reaction produces IgG-coated red cells and a positive DAT as an anamnestic antibody response develops. Cold agglutinin disease typically gives a DAT positive with anti-C3d rather than anti-IgG.

Question 23Blood Banking / Immunohematology

A patient's serum reacts with all panel cells except those that are Jk(a-b-). Which antibody is most likely present?

  1. Anti-Jka
  2. Anti-Fya
  3. Anti-Jk3 Correct answer.
  4. Anti-Jkb

Explanation

Reactivity with all cells except Jk(a-b-) cells indicates anti-Jk3, which is directed against a high-incidence antigen in the Kidd system. Anti-Jka and anti-Jkb would show selective reactivity with Jk(a+) or Jk(b+) cells.

Question 24Blood Banking / Immunohematology

A patient with a history of anti-Jka requires transfusion. Which crossmatch result would be most concerning for a hemolytic reaction?

  1. A negative immediate spin and negative antiglobulin crossmatch
  2. A positive antiglobulin crossmatch with Jk(a+) donor cells Correct answer.
  3. A negative antibody screen with Jk(a-) donor cells
  4. A positive immediate spin crossmatch with Jk(a-) donor cells

Explanation

A positive antiglobulin crossmatch with Jk(a+) donor cells indicates incompatibility with the patient's anti-Jka and could cause hemolysis. Jk(a-) units selected for the patient should be compatible.

Question 25Blood Banking / Immunohematology

A patient's red cells are group A, but the reverse typing shows weak reactions with A1 cells and strong reactions with B cells. Which additional finding would best support a subgroup of A?

  1. Positive reaction with anti-A1 lectin
  2. Positive reaction with anti-B reagent
  3. Negative reaction with anti-A reagent
  4. Positive reaction with anti-H lectin Correct answer.

Explanation

A subgroups such as A2 have increased H antigen and react strongly with anti-H lectin, while A1 cells react weakly. Anti-A1 lectin (Dolichos biflorus) agglutinates A1 cells but not A2 cells.

Question 26Blood Banking / Immunohematology

A blood bank performs an ABO forward and reverse typing on a new donor sample. The forward typing shows agglutination with anti-A and anti-B reagents, while the reverse typing shows no agglutination with either A1 or B cells. Which interpretation is most appropriate?

  1. The donor is group A with an acquired B antigen, requiring anti-A1 lectin testing.
  2. The donor is group AB, and the missing reverse grouping antibodies are expected because group AB serum lacks anti-A and anti-B. Correct answer.
  3. The donor is group B with a missing anti-A, suggesting an immunodeficient state.
  4. The donor is group O, and the forward typing is falsely positive due to rouleaux.

Explanation

In ABO typing, group AB red cells carry both A and B antigens and therefore react with both anti-A and anti-B, while the serum of a group AB person contains neither anti-A nor anti-B, so reverse typing is nonreactive with A1 and B cells. Forward and reverse results agree, confirming group AB without further workup.

Question 27Blood Banking / Immunohematology

A patient's serum is tested against a panel of reagent red cells, and reactivity is abolished after treatment of the panel cells with dithiothreitol (DTT) or 2-mercaptoethanol. Which class of antibody is most consistent with this finding?

  1. IgA antibody directed against a low-frequency antigen
  2. IgM antibody, such as anti-M or anti-P1 Correct answer.
  3. IgG antibody of the Rh system
  4. IgG antibody of the Kell system

Explanation

DTT and 2-mercaptoethanol reduce disulfide bonds in the pentameric IgM molecule, destroying its agglutinating ability, so loss of reactivity after treatment indicates an IgM antibody. IgM antibodies such as anti-M and anti-P1 are typically sulfhydryl-sensitive, whereas IgG antibodies of the Kell and Rh systems are generally resistant to these reagents.

Question 28Blood Banking / Immunohematology

A patient's serum contains anti-Jka, and two units of packed red cells are selected that are antigen-negative for Jka. The immediate spin crossmatch is compatible, but the antiglobulin-phase crossmatch shows agglutination with one of the units. Which explanation is most likely?

  1. The crossmatch reaction is due to rouleaux from excess plasma in the sample.
  2. The unit has a positive DAT caused by donor antibody coating the red cells.
  3. The patient has a warm autoantibody that reacts with all units equally.
  4. The unit carries an additional antigen that the patient's serum recognizes, such as another clinically significant antibody. Correct answer.

Explanation

When a unit is matched for the known antibody but still reacts at the antiglobulin phase, the patient's serum likely contains an additional, unidentified antibody directed against an antigen present on that donor unit. Further antibody identification is needed before transfusion. A donor positive DAT or rouleaux would not produce an isolated antiglobulin-phase incompatibility with only one unit.

Question 29Blood Banking / Immunohematology

A patient is being evaluated for a possible delayed hemolytic transfusion reaction. The DAT is positive with anti-IgG but negative with anti-C3d, and the eluate from the patient's red cells reacts with panel cells that are positive for the Jkb antigen. Which conclusion is best supported?

  1. The patient has an IgG alloantibody, most likely anti-Jkb, coating the transfused red cells. Correct answer.
  2. The patient has a cold autoantibody that binds complement at room temperature.
  3. The patient has a complement-mediated hemolysis unrelated to red cell antibodies.
  4. The patient has a warm autoantibody directed against a high-incidence antigen.

Explanation

A DAT that is positive with anti-IgG but negative with anti-C3d indicates IgG coating of red cells without complement fixation, consistent with an IgG alloantibody. An eluate that reacts specifically with Jkb-positive cells identifies anti-Jkb, supporting a delayed hemolytic transfusion reaction. Warm autoantibodies typically react with all panel cells rather than showing antigen specificity.

Question 30Blood Banking / Immunohematology

A patient's serum reacts with all panel cells at the antiglobulin phase, and the autocontrol is also positive. The patient has not been transfused recently. Which next step is most useful in distinguishing a warm autoantibody from an alloantibody masked by panreactivity?

  1. Perform an elution and test the eluate against a panel of reagent red cells.
  2. Perform adsorption studies with the patient's own red cells or allogeneic red cells to remove autoantibody. Correct answer.
  3. Repeat the antibody screen using saline-suspended cells at immediate spin only.
  4. Titer the serum against a single panel cell to determine antibody strength.

Explanation

When panreactivity with a positive autocontrol suggests a warm autoantibody, adsorption studies using the patient's own (autologous) red cells or allogeneic red cells remove the autoantibody and allow detection of any underlying alloantibody. This is essential before selecting antigen-negative units. Titration or immediate-spin testing does not resolve the masking problem.

Question 31Clinical Chemistry

A serum sample is visibly hemolyzed. Which analyte is most likely to be falsely elevated as a direct result of red cell lysis?

  1. Albumin
  2. Chloride
  3. Potassium Correct answer.
  4. Sodium

Explanation

Intracellular potassium concentration is roughly 25 times higher than plasma, so rupture of erythrocytes releases potassium into the serum and produces a spurious hyperkalemia. Sodium and chloride are predominantly extracellular and change little, and albumin is not concentrated inside red cells.

Question 32Clinical Chemistry

Which lipoprotein fraction is measured directly by homogeneous assay when calculating a non-HDL cholesterol result?

  1. HDL cholesterol Correct answer.
  2. Chylomicron triglyceride
  3. Apolipoprotein B-48
  4. Lipoprotein(a)

Explanation

Non-HDL cholesterol is total cholesterol minus HDL cholesterol, so an accurate HDL value is the direct measurement required. The subtraction captures cholesterol carried by all atherogenic particles (LDL, VLDL, IDL, Lp(a)) without measuring each one separately.

Question 33Clinical Chemistry

The reference method for serum glucose measurement, against which routine methods are standardized, is based on which principle?

  1. Hexokinase with glucose-6-phosphate dehydrogenase Correct answer.
  2. Ion-selective electrode
  3. Jaffe reaction
  4. Alkaline picrate

Explanation

The hexokinase/glucose-6-phosphate dehydrogenase method is the reference procedure because it is highly specific for glucose and measures NADH stoichiometrically at 340 nm. Other methods are compared against it through traceability programs.

Question 34Clinical Chemistry

A patient's total calcium is 8.0 mg/dL and albumin is 2.0 g/dL. Using the conventional correction of adding 0.8 mg/dL per 1.0 g/dL of albumin below 4.0 g/dL, what is the albumin-corrected calcium?

  1. 9.6 mg/dL Correct answer.
  2. 6.4 mg/dL
  3. 10.4 mg/dL
  4. 8.0 mg/dL

Explanation

The albumin deficit is 4.0 minus 2.0, or 2.0 g/dL, which is multiplied by 0.8 to give 1.6 mg/dL. Adding 1.6 to the measured 8.0 mg/dL yields a corrected value of 9.6 mg/dL.

Question 35Clinical Chemistry

Which enzyme pattern is most characteristic of a cholestatic (biliary) rather than hepatocellular injury?

  1. Marked aspartate aminotransferase elevation
  2. Low pseudocholinesterase activity
  3. Marked alanine aminotransferase elevation
  4. Marked alkaline phosphatase and gamma-glutamyl transferase elevation Correct answer.

Explanation

Biliary obstruction increases synthesis and release of canalicular enzymes, so alkaline phosphatase and gamma-glutamyl transferase rise disproportionately. Transaminases rise mainly when hepatocytes are damaged, as in viral or toxic hepatitis.

Question 36Clinical Chemistry

A 24-hour urine specimen for metanephrines is collected into a container without acid preservative. Which preanalytical problem is most likely?

  1. Catecholamine and metanephrine degradation from alkaline pH Correct answer.
  2. Photodegradation of creatinine
  3. Loss of analyte by volatilization
  4. Bacterial overgrowth producing false elevation

Explanation

Catecholamines and their metabolites are unstable at alkaline pH and oxidize readily, so acid is added to keep the urine at about pH 4 or below. Without acidification, falsely low results from degradation are the main concern.

Question 37Clinical Chemistry

Which analyte requires collection in a tube with EDTA and prompt separation from cells because glycolysis by erythrocytes lowers the result?

  1. Plasma glucose Correct answer.
  2. Serum sodium
  3. Serum creatinine
  4. Total protein

Explanation

Erythrocytes continue to consume glucose in vitro, so plasma glucose falls by roughly 5 to 7 percent per hour at room temperature unless cells are removed or glycolysis is inhibited. Sodium, creatinine, and total protein are not consumed by cellular metabolism.

Question 38Clinical Chemistry

A patient with severe vomiting presents with a blood pH of 7.52, PCO2 of 48 mmHg, and bicarbonate of 38 mmol/L. Which acid-base disturbance is present?

  1. Mixed respiratory and metabolic acidosis
  2. Respiratory alkalosis
  3. Metabolic acidosis with respiratory compensation
  4. Metabolic alkalosis with respiratory compensation Correct answer.

Explanation

The elevated pH and elevated bicarbonate indicate a primary metabolic alkalosis, and the raised PCO2 reflects hypoventilation as respiratory compensation. Loss of gastric hydrochloric acid is a classic cause of this pattern.

Question 39Clinical Chemistry

In the Jaffe reaction for creatinine, which substance is the principal cause of a positive interference in serum?

  1. Glucose Correct answer.
  2. Urea
  3. Ascorbic acid
  4. Bilirubin

Explanation

Glucose forms a chromogen with alkaline picrate and produces falsely high creatinine values in the classic Jaffe method. Kinetic or enzymatic methods reduce this interference, which is clinically relevant in diabetic patients with very high glucose.

Question 40Clinical Chemistry

A troponin result is reported as 0.04 ng/mL with a 99th percentile upper reference limit of 0.02 ng/mL, and the assay's limit of detection is 0.01 ng/mL. How should this result be interpreted?

  1. It is below the limit of detection and should be reported as undetectable
  2. It is a false positive because values below 0.10 ng/mL are never clinically meaningful
  3. It exceeds the 99th percentile URL and is consistent with myocardial injury if the clinical picture fits Correct answer.
  4. It is within the reference interval and excludes acute coronary syndrome

Explanation

The value is above the limit of detection and above the assay-specific 99th percentile URL, so it meets the biochemical definition of myocardial injury. Whether it represents acute myocardial infarction depends on a rising or falling pattern plus clinical evidence of ischemia.

Question 41Clinical Chemistry

Which condition produces a falsely low serum total protein result when measured by the biuret method?

  1. Sample stored at room temperature overnight
  2. Prolonged tourniquet application
  3. Hemolysis
  4. Severe lipemia Correct answer.

Explanation

Lipemia causes turbidity that scatters light and, depending on the instrument's blanking, can produce falsely low biuret protein values. Hemolysis and hemoconcentration from prolonged stasis tend to raise the result rather than lower it.

Question 42Clinical Chemistry

In a patient with nephrotic syndrome, which pattern of serum protein electrophoresis is expected?

  1. Normal albumin with a monoclonal spike in the gamma region
  2. Low albumin with low alpha-2 globulin
  3. Low gamma globulin with normal albumin
  4. Low albumin with increased alpha-2 globulin Correct answer.

Explanation

Nephrotic syndrome causes urinary loss of albumin and other small proteins, so albumin falls. Compensatory hepatic synthesis of large proteins such as alpha-2-macroglobulin raises the alpha-2 fraction, producing the classic low albumin/high alpha-2 pattern.

Question 43Clinical Chemistry

Which analyte is the most appropriate first-line biochemical marker for assessing long-term glycemic control over the preceding two to three months?

  1. Fructosamine
  2. Hemoglobin A1c Correct answer.
  3. 1,5-anhydroglucitol
  4. Glycated albumin

Explanation

Hemoglobin A1c reflects glucose exposure over the lifespan of the erythrocyte, roughly 120 days, so it represents the prior two to three months. Fructosamine and glycated albumin reflect shorter intervals of about two to three weeks.

Question 44Clinical Chemistry

A fasting patient has a plasma glucose of 118 mg/dL on two separate occasions. According to standard diagnostic criteria, this finding is best classified as which?

  1. Impaired fasting glucose Correct answer.
  2. Diabetes mellitus
  3. Normal glucose tolerance
  4. Hypoglycemia

Explanation

A fasting plasma glucose between 100 and 125 mg/dL defines impaired fasting glucose, a prediabetic state. Diabetes requires a fasting value of 126 mg/dL or higher, and normal fasting glucose is below 100 mg/dL.

Question 45Clinical Chemistry

Which laboratory finding is most consistent with primary hyperparathyroidism?

  1. Low calcium with low PTH
  2. Elevated calcium with suppressed PTH
  3. Low calcium with elevated PTH
  4. Elevated calcium with elevated or inappropriately normal PTH Correct answer.

Explanation

In primary hyperparathyroidism, autonomous PTH secretion raises serum calcium, and PTH fails to suppress despite the hypercalcemia. A suppressed PTH with hypercalcemia instead points to a non-parathyroid cause such as malignancy.

Question 46Clinical Chemistry

Which statement correctly describes the relationship between serum osmolality and the osmolal gap?

  1. The osmolal gap is measured osmolality multiplied by the number of solutes
  2. The osmolal gap is the difference between measured osmolality and calculated osmolality Correct answer.
  3. The osmolal gap is the sum of measured and calculated osmolality
  4. The osmolal gap is calculated osmolality divided by measured osmolality

Explanation

Calculated osmolality uses sodium, glucose, and urea, so the gap between measured and calculated values reveals unmeasured solutes. An elevated gap suggests ingestion of an osmotically active substance such as methanol, ethylene glycol, or isopropanol.

Question 47Clinical Chemistry

A urine specimen has a specific gravity of 1.040 by refractometry but a reagent strip specific gravity of 1.015. Which explanation is most likely?

  1. The specimen contains high concentrations of radiologic contrast medium Correct answer.
  2. The specimen is contaminated with bacteria
  3. The specimen was collected at room temperature
  4. The reagent strip was read at the wrong time

Explanation

Refractometry responds to all dissolved solutes, whereas reagent strip specific gravity depends mainly on ionizable substances. Radiographic contrast media are large nonionic molecules that raise refractive index without proportionally raising the strip value.

Question 48Clinical Chemistry

Which hemoglobin variant migrates differently on alkaline electrophoresis and is classically associated with sickle cell trait?

  1. Hemoglobin S Correct answer.
  2. Hemoglobin A2
  3. Hemoglobin F
  4. Hemoglobin C

Explanation

Hemoglobin S results from a glutamic acid to valine substitution in the beta chain and migrates more slowly than hemoglobin A toward the anode at alkaline pH. Sickle cell trait shows both A and S bands, while sickle cell disease shows predominantly S.

Question 49Clinical Chemistry

Which factor most directly determines the reference interval for a laboratory test?

  1. The instrument manufacturer's name
  2. The distribution of results in a defined healthy reference population Correct answer.
  3. The reagent lot number in use
  4. The number of tests performed per day

Explanation

A reference interval is derived statistically from results in a carefully defined healthy population, usually spanning the central 95 percent of values. Instrument and reagent factors affect method performance but do not define the population-based interval.

Question 50Clinical Chemistry

A serum sample for bilirubin is exposed to bright light before analysis. What is the expected effect?

  1. Bilirubin decreases because it is photodegraded Correct answer.
  2. Bilirubin becomes conjugated and increases
  3. Bilirubin is unchanged because light does not affect it
  4. Bilirubin increases because light converts bilirubin to biliverdin

Explanation

Bilirubin is light sensitive and degrades with exposure to visible light, which is the basis of phototherapy for neonatal jaundice. Samples should be protected from light to avoid falsely low results.