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Question 1Blood Bank / Immunohematology

Anti-A and anti-B antibodies in the serum of a group O individual belong predominantly to which immunoglobulin class?

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

Explanation

Naturally occurring ABO antibodies are predominantly IgM, which agglutinate red cells in saline at room temperature and fix complement efficiently. This is why ABO incompatibility can cause immediate intravascular hemolysis.

Question 2Blood Bank / Immunohematology

A trauma patient in hemorrhagic shock has no ABO type on file at the blood bank. Which red cell component is most appropriate for immediate release?

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

Explanation

Group O red cells lack both A and B antigens, so they survive in recipients of any ABO type before the patient's type is known. Group O (Rh-negative where feasible) is the classic emergency-release red cell component.

Question 3Blood Bank / Immunohematology

Whole blood-derived and apheresis red cell units must be stored within which temperature range?

  1. 20–24 °C
  2. 37 °C
  3. 1–6 °C Correct answer.
  4. −18 °C or colder

Explanation

Red cells are stored at 1–6 °C, which slows glycolysis and limits the growth of most bacterial contaminants. Storage below or above this range shortens red cell survival and raises the risk of transfusion reactions.

Question 4Blood Bank / Immunohematology

Platelet concentrates are stored under which set of conditions?

  1. 20–24 °C with continuous agitation Correct answer.
  2. −18 °C or colder
  3. 1–6 °C
  4. 37 °C

Explanation

Platelets require room temperature storage (20–24 °C) with continuous gentle agitation to maintain viability and gas exchange. Refrigeration causes platelet shape change and rapid loss of function.

Question 5Blood Bank / Immunohematology

The major crossmatch consists of combining which two components?

  1. Donor serum and recipient red cells
  2. Donor serum and donor red cells
  3. Recipient serum and donor plasma
  4. Recipient serum and donor red cells Correct answer.

Explanation

The major crossmatch tests recipient serum against donor red cells to detect antibodies in the recipient that could destroy the transfused cells; it is the clinically important part of compatibility testing. The minor crossmatch tests donor serum against recipient cells.

Question 6Blood Bank / Immunohematology

Rh immune globulin given to an Rh-negative mother is directed against which antigen?

  1. K (Kell)
  2. Fya (Duffy)
  3. E (Rh)
  4. D (Rh) Correct answer.

Explanation

Rh immune globulin contains anti-D, which clears fetal D-positive red cells from the maternal circulation before the mother can mount an immune response. This prevents formation of maternal anti-D and subsequent hemolytic disease of the newborn.

Question 7Blood Bank / Immunohematology

Which antibody is the most common cause of severe hemolytic disease of the fetus and newborn?

  1. Anti-M
  2. Anti-D Correct answer.
  3. Anti-P1
  4. Anti-Lea

Explanation

Anti-D is a placental-transferable IgG antibody that binds fetal D-positive red cells and causes their destruction, producing the classic severe form of hemolytic disease of the newborn. Prophylaxis with Rh immune globulin has reduced but not eliminated its occurrence.

Question 8Blood Bank / Immunohematology

A pretransfusion antibody screen is positive. What is the appropriate next step?

  1. Transfuse group O uncrossmatched red cells
  2. Perform a direct antiglobulin test as the only further step
  3. Repeat the type and screen in 24 hours
  4. Perform an antibody identification panel Correct answer.

Explanation

A positive antibody screen requires identification of the offending antibody using a panel of phenotyped reagent red cells, so that antigen-negative units can be selected. Identification guides both unit selection and assessment of clinical significance.

Question 9Blood Bank / Immunohematology

Red cells that type as D-negative at immediate spin are often retested with anti-D at the antihuman globulin phase. What is the purpose of this weak D test?

  1. To detect red cells with weak expression of the D antigen that fail to agglutinate at immediate spin Correct answer.
  2. To determine the patient's ABO subgroup
  3. To measure complement bound to the red cell surface
  4. To detect anti-D in the patient's serum

Explanation

Some red cells express D antigen too weakly to agglutinate with anti-D at immediate spin but react after antiglobulin enhancement. Identifying weak D expression prevents misclassification as D-negative and avoids unnecessary Rh immune globulin in donors and patients.

Question 10Blood Bank / Immunohematology

Which characteristic best identifies a red cell antibody as likely to be clinically significant in transfusion?

  1. Reacts at 37 °C or by the indirect antiglobulin technique Correct answer.
  2. Is detectable only in saliva
  3. Reacts only at immediate spin at room temperature
  4. Is IgM and avidly fixes complement

Explanation

Antibodies that react at 37 °C or in the antiglobulin phase are typically IgG, are active at body temperature, and can mediate destruction of transfused cells. Antibodies reacting only at room temperature are usually clinically insignificant.

Question 11Blood Bank / Immunohematology

Polyspecific antihuman globulin reagent used in the indirect antiglobulin test contains antibodies directed against which substances?

  1. IgM and IgA heavy chains
  2. Human albumin and fibrinogen
  3. IgG and the complement component C3d Correct answer.
  4. A and B blood group antigens

Explanation

Polyspecific antihuman globulin contains anti-IgG and anti-C3d, allowing detection of red cells coated with IgG, complement, or both. Monospecific reagents contain only one of these specificities.

Question 12Blood Bank / Immunohematology

Which set of characteristics correctly describes anti-Lea?

  1. IgG; binds complement; causes intravascular hemolysis
  2. IgG; crosses the placenta; causes severe hemolytic disease of the newborn
  3. IgM; reacts optimally at 37 °C; clinically significant
  4. IgM; does not cross the placenta; rarely clinically significant Correct answer.

Explanation

Lewis antibodies are IgM, react optimally at room temperature or cooler, and do not cross the placenta. Lewis antigens are also poorly developed on fetal red cells, so anti-Lea is not associated with hemolytic disease of the newborn.

Question 13Blood Bank / Immunohematology

A cold autoagglutinin with anti-I specificity is most commonly associated with which condition?

  1. Mycoplasma pneumoniae infection Correct answer.
  2. Paroxysmal nocturnal hemoglobinuria
  3. Hemolytic disease of the newborn
  4. Warm autoimmune hemolytic anemia

Explanation

Anti-I is a common cold autoantibody that can rise to high titer after Mycoplasma pneumoniae infection, producing cold agglutinin syndrome. In contrast, anti-i is associated with infectious mononucleosis.

Question 14Blood Bank / Immunohematology

Soluble ABO substances can be detected in the saliva of an individual who is which of the following?

  1. Of the Bombay (Oh) phenotype
  2. Rh-negative (rr)
  3. A non-secretor (se/se)
  4. A secretor (Se/Se or Se/se) Correct answer.

Explanation

The Se gene controls expression of H, A, and B glycoproteins in secretions; individuals with at least one Se allele produce soluble blood group substances in saliva. Non-secretors lack these soluble substances.

Question 15Blood Bank / Immunohematology

Which statement about anti-K (Kell) is accurate?

  1. It is directed against a high-incidence antigen present on nearly all donor units
  2. It reacts only at immediate spin and never at 37 °C
  3. It is an IgG antibody capable of causing hemolytic disease of the newborn Correct answer.
  4. It is a naturally occurring IgM antibody with no clinical significance

Explanation

Anti-K is typically an immune-stimulated IgG antibody that reacts at 37 °C and the antiglobulin phase, and it crosses the placenta to cause hemolytic disease of the newborn. Because Kell antigens are well expressed on fetal red cells, affected fetuses may be anemic with relatively little bilirubin elevation.

Question 16Blood Bank / Immunohematology

A Kleihauer-Betke stain is performed on a postpartum Rh-negative woman in order to:

  1. Estimate the volume of fetal red cells in the maternal circulation Correct answer.
  2. Detect maternal red cells in the fetal circulation
  3. Determine the fetal ABO group
  4. Measure the mother's anti-D titer

Explanation

The Kleihauer-Betke acid elution stain distinguishes fetal hemoglobin-containing cells from adult cells, allowing an estimate of fetomaternal hemorrhage volume. That estimate is used to calculate whether additional Rh immune globulin is needed.

Question 17Blood Bank / Immunohematology

Cellular blood components are gamma irradiated before transfusion in order to prevent:

  1. Bacterial proliferation during storage
  2. Febrile nonhemolytic transfusion reactions
  3. Alloimmunization to HLA antigens
  4. Transfusion-associated graft-versus-host disease Correct answer.

Explanation

Irradiation inactivates donor T lymphocytes so they cannot engraft and attack recipient tissues, preventing transfusion-associated graft-versus-host disease. It is indicated for immunocompromised recipients and for directed donations from blood relatives.

Question 18Blood Bank / Immunohematology

Cryoprecipitated antihemophilic factor is the preferred transfused source of which protein in a patient with hypofibrinogenemia?

  1. Protein C
  2. Fibrinogen Correct answer.
  3. Antithrombin
  4. Albumin

Explanation

Cryoprecipitate is rich in fibrinogen, factor VIII, von Willebrand factor, factor XIII, and fibronectin, making it the traditional product for fibrinogen replacement. It is prepared from fresh frozen plasma by thawing at 1–6 °C and retaining the precipitate.

Question 19Blood Bank / Immunohematology

Plasma from which ABO group is compatible with recipients of every ABO group?

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

Explanation

Group AB plasma contains neither anti-A nor anti-B, so it will not hemolyze recipient red cells regardless of the recipient's ABO type. Group O is the universal donor for red cells, while group AB is the universal donor for plasma.

Question 20Blood Bank / Immunohematology

A patient with warm autoimmune hemolytic anemia has a panreactive antibody screen. Which technique is most useful for uncovering a possible underlying alloantibody?

  1. Direct antiglobulin test using anti-C3d only
  2. Replacement of the patient's serum with saline
  3. Neutralization of the serum with soluble Lewis substance
  4. Adsorption of the patient's serum with autologous red cells Correct answer.

Explanation

Autologous adsorption removes the warm autoantibody from the serum, leaving any underlying alloantibody free to react with panel cells. Allogeneic adsorption with phenotyped donor cells is used when the patient has been recently transfused.

Question 21Blood Bank / Immunohematology

A patient's red cells are nonreactive with anti-A, anti-B, and anti-A,B, but the serum agglutinates all group O reagent cells tested. Which finding would confirm the Bombay (Oh) phenotype?

  1. Absence of D antigen on the red cells
  2. Absence of I antigen on the red cells
  3. Absence of H antigen on the red cells Correct answer.
  4. Absence of A antigen on the red cells

Explanation

Bombay individuals inherit two nonfunctional H alleles, so their cells lack H and cannot express A or B even when A or B transferase genes are present. Their serum contains anti-H, which agglutinates all red cells except other Oh cells, explaining the panreactivity.

Question 22Blood Bank / Immunohematology

Reagent red cells treated with the proteolytic enzyme ficin are used during antibody identification because enzyme treatment:

  1. Destroys all IgG antibodies present in the patient's serum
  2. Enhances Rh, Kidd, and Lewis reactivity while destroying Duffy and MNS antigens Correct answer.
  3. Has no measurable effect on any blood group antigen system
  4. Destroys Rh and Kidd antigens while preserving Duffy and MNS antigens

Explanation

Proteases such as ficin, papain, and bromelin cleave sialic acid–rich glycoproteins, enhancing antigens of the Rh, Kidd, Lewis, and P1 systems while destroying Duffy, M and N, and Xga determinants. Comparing enzyme-treated and untreated panels helps confirm antibody specificity.

Question 23Blood Bank / Immunohematology

Treatment of a patient's serum with dithiothreitol (DTT) is used to determine which property of a red cell antibody?

  1. The antibody's titer
  2. Whether the antibody binds complement
  3. Whether the antibody is of the IgM or IgG class Correct answer.
  4. The antibody's specificity within the Rh system

Explanation

DTT reduces disulfide bonds and disrupts the pentameric structure of IgM, abolishing its agglutinating activity while leaving most IgG antibodies reactive. Loss of reactivity after DTT treatment therefore indicates an IgM antibody.

Question 24Blood Bank / Immunohematology

A patient's red cells agglutinate with anti-A but not with the anti-A1 lectin (Dolichos biflorus), and the serum agglutinates A1 cells but not A2 cells. What is the most likely explanation?

  1. The patient is group B with an acquired B antigen
  2. The patient is group A1 with an autoanti-A
  3. The patient is group O with a missing anti-A
  4. The patient is group A2 with anti-A1 in the serum Correct answer.

Explanation

About 1–2% of group A2 individuals produce an IgM anti-A1 that reacts with A1 cells but not with A2 cells, producing a discrepancy between forward and reverse grouping. The antibody is generally not clinically significant, but A2 or group O red cells are selected if transfusion is needed.

Question 25Blood Bank / Immunohematology

In a pregnancy monitored for anti-D, an indirect antiglobulin titer at or above which value is generally considered the critical titer that prompts further fetal assessment?

  1. 1:16 Correct answer.
  2. 1:1024
  3. 1:64
  4. 1:256

Explanation

A critical titer of 1:16 (some laboratories use 1:32) is the conventional threshold above which the risk of significant fetal anemia rises and additional evaluation such as middle cerebral artery Doppler is considered. Titers below this level are associated with a low likelihood of severe disease.

Question 26Blood Bank / Immunohematology

A patient's serum agglutinates all group O reagent red cells, including cord cells, at room temperature, and the patient's own red cells are nonreactive with Ulex europaeus lectin. Which antibody is most likely present?

  1. Anti-Lua
  2. Anti-H Correct answer.
  3. Anti-P1
  4. Anti-M

Explanation

The Bombay phenotype (Oh) lacks H antigen on red cells, so the patient can produce anti-H, which reacts with H-bearing red cells from essentially all other individuals. Ulex europaeus lectin detects H antigen and is nonreactive with Bombay cells. Anti-H agglutinates group O adult and cord red cells because both express H.

Question 27Clinical Chemistry

Which collection tube is preferred when a fasting glucose specimen cannot be analyzed promptly and glycolysis must be inhibited?

  1. Fluoride-oxalate tube Correct answer.
  2. Potassium EDTA tube
  3. Heparinized plasma tube
  4. Sodium citrate tube

Explanation

Fluoride blocks enolase, the enzyme that drives glycolysis in erythrocytes, so glucose stays stable for hours at room temperature. Oxalate is included to prevent clotting. Plain heparin or EDTA tubes do not stop cellular glucose consumption.

Question 28Clinical Chemistry

A colored solution in a 1 cm cuvette transmits 10% of the incident light at 340 nm. What is its absorbance?

  1. 0.1
  2. 2.0
  3. 10.0
  4. 1.0 Correct answer.

Explanation

Absorbance equals the negative logarithm of transmittance, so a transmittance of 0.10 gives an absorbance of 1.0. Absorbance rises as transmittance falls, but the relation is logarithmic rather than linear.

Question 29Clinical Chemistry

Unconjugated bilirubin is transported in plasma primarily bound to which protein?

  1. Transferrin
  2. Prealbumin
  3. Albumin Correct answer.
  4. Haptoglobin

Explanation

Unconjugated bilirubin is water insoluble and travels tightly bound to albumin until it reaches the liver for glucuronidation. Binding limits glomerular filtration and tissue deposition.

Question 30Clinical Chemistry

Which serum enzyme is the more liver-specific indicator of hepatocellular injury?

  1. Alanine aminotransferase Correct answer.
  2. Creatine kinase
  3. Aspartate aminotransferase
  4. Alkaline phosphatase

Explanation

Alanine aminotransferase is concentrated in hepatocyte cytoplasm with little content in skeletal muscle, making it more specific for liver injury. Aspartate aminotransferase is also abundant in muscle and erythrocytes.

Question 31Clinical Chemistry

Which endogenous analyte is most widely used to estimate glomerular filtration rate in routine chemistry panels?

  1. Urea
  2. Amylase
  3. Creatinine Correct answer.
  4. Uric acid

Explanation

Creatinine is produced at a relatively steady rate from muscle creatine and is cleared largely by glomerular filtration, so its serum concentration tracks GFR. Urea is influenced too strongly by hydration, protein intake, and hepatic function.

Question 32Clinical Chemistry

An arterial blood gas result shows a pH of 7.28. How is this value classified?

  1. Respiratory compensation
  2. Alkalemia
  3. Acidemia Correct answer.
  4. Normal acid-base status

Explanation

The reference interval for arterial pH is approximately 7.35 to 7.45, so a value below 7.35 represents acidemia. Compensation is a physiologic response and cannot be identified from the pH alone.

Question 33Clinical Chemistry

In vitro hemolysis most markedly produces a falsely elevated result for which analyte?

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

Explanation

Erythrocytes contain potassium at a concentration roughly 25 times that of plasma, so lysis releases a large amount into the supernatant. Sodium and chloride are predominantly extracellular and change far less.

Question 34Clinical Chemistry

A patient has a total calcium of 8.0 mg/dL and an albumin of 2.0 g/dL. Using the standard correction of 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. 7.2 mg/dL
  3. 8.8 mg/dL
  4. 10.4 mg/dL

Explanation

The albumin deficit is 2.0 g/dL, which adds 1.6 mg/dL to the measured calcium, giving 9.6 mg/dL. About half of total calcium is albumin bound, so low albumin lowers total calcium without changing the ionized fraction.

Question 35Clinical Chemistry

A serum sample gives sodium 140 mmol/L, chloride 105 mmol/L, and bicarbonate 15 mmol/L. What is the anion gap?

  1. 30 mmol/L
  2. 35 mmol/L
  3. 20 mmol/L Correct answer.
  4. 10 mmol/L

Explanation

The anion gap is sodium minus the sum of chloride and bicarbonate: 140 minus 120 equals 20 mmol/L. A value above roughly 12 mmol/L suggests accumulation of unmeasured anions such as ketones, lactate, or uremic toxins.

Question 36Clinical Chemistry

A serum sample has a measured osmolality of 320 mOsm/kg and a calculated osmolality of 290 mOsm/kg. What does this finding most likely indicate?

  1. Unmeasured osmole such as methanol Correct answer.
  2. Evaporation from the specimen
  3. Normal result, no action needed
  4. Analytical sodium error

Explanation

An osmolal gap above about 10 mOsm/kg reflects solute that is not accounted for by sodium, glucose, and urea. Volatile alcohols and other low-molecular-weight substances widen the gap.

Question 37Clinical Chemistry

Using the Friedewald relationship, what is the LDL cholesterol for a patient with total cholesterol 240 mg/dL, HDL cholesterol 40 mg/dL, and triglycerides 150 mg/dL?

  1. 200 mg/dL
  2. 170 mg/dL Correct answer.
  3. 150 mg/dL
  4. 50 mg/dL

Explanation

LDL cholesterol is estimated as total cholesterol minus HDL cholesterol minus triglycerides divided by 5: 240 minus 40 minus 30 equals 170 mg/dL. The calculation assumes triglycerides are below 400 mg/dL and is unreliable in severe hypertriglyceridemia.

Question 38Clinical Chemistry

Which set of thyroid function results is most consistent with untreated primary hypothyroidism?

  1. High free T4, high TSH
  2. High free T4, low TSH
  3. Low free T4, low TSH
  4. Low free T4, high TSH Correct answer.

Explanation

Failure of the thyroid gland lowers free T4, and the loss of negative feedback drives pituitary TSH upward. The combination of low free hormone with elevated TSH localizes the defect to the thyroid.

Question 39Clinical Chemistry

Which condition can produce a falsely low hemoglobin A1c result relative to the true glycemic average?

  1. Iron deficiency anemia
  2. Chronic hemolytic anemia Correct answer.
  3. Recent transient hyperglycemia
  4. Untreated diabetes mellitus

Explanation

Hemoglobin A1c reflects glucose exposure over the life of the erythrocyte, so shortened red cell survival reduces glycation and lowers the result. Iron deficiency anemia tends to have the opposite effect because older cells circulate longer.

Question 40Clinical Chemistry

How does severe lipemia most commonly interfere with a spectrophotometric chemistry assay?

  1. It chelates calcium in the reagent mixture
  2. It scatters light and raises apparent absorbance Correct answer.
  3. It alters the pH of the reaction buffer
  4. It competes with the analyte for reagent

Explanation

Lipid particles scatter light and behave like turbidity, adding to the measured absorbance and biasing results upward or causing reagent blank failure. High-speed centrifugation or a lipemia-clearing reagent is used to remove the effect.

Question 41Clinical Chemistry

A single quality control observation exceeds the mean by more than 3 standard deviations. Which type of error does this rule detect?

  1. A shift in the mean
  2. Random error Correct answer.
  3. A gradual trend
  4. Systematic error

Explanation

The 1-3s rule flags a single point beyond three standard deviations, an event typical of random error such as a pipetting anomaly. Systematic problems are better detected by rejection rules involving consecutive points, such as 2-2s, 4-1s, or 10x.

Question 42Clinical Chemistry

Which substance is a classic positive interferent in the alkaline picrate (Jaffe) method for creatinine?

  1. Sodium
  2. Acetoacetate Correct answer.
  3. Chloride
  4. Urea

Explanation

The Jaffe reaction measures all chromogens that react with picrate in alkaline solution, including ketone bodies such as acetoacetate. Enzymatic creatinine methods are less susceptible to this interference.

Question 43Clinical Chemistry

A cerebrospinal fluid glucose is 30 mg/dL with a simultaneous serum glucose of 100 mg/dL. Which condition best fits this pattern?

  1. Bacterial meningitis Correct answer.
  2. Multiple sclerosis
  3. Viral meningitis
  4. Normal finding

Explanation

The CSF-to-serum glucose ratio is normally about 0.6, whereas bacterial meningitis typically lowers it below 0.4 as organisms and neutrophils consume glucose. Viral meningitis usually leaves the ratio near normal.

Question 44Clinical Chemistry

After myocardial injury, how soon does cardiac troponin typically begin to rise above the upper reference limit?

  1. Within 3 to 6 hours Correct answer.
  2. Within 15 minutes
  3. Only after 24 hours
  4. After 7 days

Explanation

High-sensitivity troponin assays detect release within about 3 to 6 hours of symptom onset, with concentrations remaining elevated for several days. This early rise supports rapid triage of suspected acute coronary syndrome.

Question 45Clinical Chemistry

Serum protein electrophoresis shows a narrow, dense band in the gamma region. Which interpretation is most appropriate?

  1. Iron deficiency anemia
  2. Monoclonal gammopathy Correct answer.
  3. Acute inflammation
  4. Nephrotic syndrome

Explanation

A restricted, sharp band in the gamma region represents a single immunoglobulin clone and prompts evaluation for multiple myeloma or related disorders. Polyclonal increases from inflammation produce a broad, diffuse gamma rise instead.

Question 46Clinical Chemistry

When is the appropriate time to draw a vancomycin trough concentration?

  1. 30 minutes after the infusion ends
  2. 2 hours after the infusion ends
  3. Just before the next scheduled dose Correct answer.
  4. At any point in the dosing interval

Explanation

Trough concentrations are measured at steady state immediately before the next dose, when drug levels are lowest. This timing allows comparison with the target range for efficacy and nephrotoxicity monitoring.

Question 47Clinical Chemistry

A patient has an anion gap of 10 mmol/L and an albumin of 2.0 g/dL. Using a correction of 2.5 mmol/L per 1.0 g/dL of albumin below 4.0 g/dL, what is the albumin-corrected anion gap?

  1. 5 mmol/L
  2. 10 mmol/L
  3. 15 mmol/L Correct answer.
  4. 20 mmol/L

Explanation

Albumin carries most of the unmeasured negative charge, so a low albumin masks an elevated anion gap. The deficit of 2.0 g/dL adds 5 mmol/L, giving a corrected gap of 15 mmol/L and revealing a hidden high-anion-gap acidosis.

Question 48Clinical Chemistry

A patient with marked hyperproteinemia has a serum sodium of 128 mmol/L by indirect ion-selective electrode, normal measured osmolality, and a sodium of 140 mmol/L by direct ion-selective electrode. What is the best explanation?

  1. Pseudohyponatremia from reduced plasma water Correct answer.
  2. Sodium loss from diuretic therapy
  3. True hyponatremia from SIADH
  4. Hyperglycemia-induced dilutional hyponatremia

Explanation

Indirect ion-selective electrodes measure sodium in a diluted sample, so a large nonaqueous protein or lipid volume displaces plasma water and falsely lowers the reported concentration. Direct electrodes and normal osmolality confirm that the sodium concentration in plasma water is actually normal.

Question 49Clinical Chemistry

A patient has a persistently elevated serum amylase, a normal lipase, no abdominal symptoms, and normal renal function. Which explanation is most likely?

  1. Acute pancreatitis
  2. Renal failure
  3. Mumps parotitis
  4. Macroamylasemia Correct answer.

Explanation

Macroamylase is an immunoglobulin-bound complex that escapes glomerular filtration and accumulates in plasma, producing a chronic isolated amylase elevation. Lipase is normal and the patient is asymptomatic, which distinguishes this benign entity from true pancreatic disease.

Question 50Clinical Chemistry

An immunometric assay reports an unexpectedly low result for a specimen that contains an extremely high concentration of the analyte. Which phenomenon explains this?

  1. Cross-reactivity
  2. Matrix effect
  3. Carryover
  4. Hook effect Correct answer.

Explanation

When analyte is present in vast excess, it saturates both capture and detection antibodies separately, preventing sandwich formation and producing a falsely low signal. Serial dilution reveals the true concentration by bringing the analyte into the measurable range.