I85PREP
⌘ K
ASCP MLS study materials
ASCP MLS study resources

ASCP MLS practice questions

One question at a time. Build your ASCP MLS understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Blood Bank / Immunohematology

A unit of red blood cells collected in CPDA-1 and stored at 1–6 °C has a maximum shelf life of:

  1. 7 days
  2. 21 days
  3. 35 days Correct answer.
  4. 42 days

Explanation

Red cells anticoagulated with CPDA-1 may be stored at 1–6 °C for up to 35 days; additive solutions such as AS-1, AS-3, and AS-5 extend storage to 42 days. Storage beyond the licensed dating interval is not permitted because of progressive loss of viability and rise in plasma potassium.

Question 2Blood Bank / Immunohematology

A patient's red cells agglutinate with anti-A reagent but not with anti-B reagent, and the serum agglutinates reagent B cells but not reagent A cells. The patient's ABO group is:

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

Explanation

Forward grouping shows the A antigen on the cells and no B antigen, and reverse grouping confirms the expected anti-B in the serum. Concordant forward and reverse results define group A.

Question 3Blood Bank / Immunohematology

Rh immune globulin should be administered to an unsensitized Rh-negative mother after delivery of an Rh-positive infant within:

  1. 7 days
  2. 24 hours
  3. 14 days
  4. 72 hours Correct answer.

Explanation

A standard 300 µg dose of Rh immune globulin given within 72 hours of delivery clears fetal Rh-positive cells before the mother can mount an immune response. A Kleihauer–Betke or flow cytometric screen determines whether the dose must be increased for a large fetomaternal hemorrhage.

Question 4Blood Bank / Immunohematology

Platelet concentrates stored at 20–24 °C with continuous agitation have a maximum shelf life of:

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

Explanation

Platelets are stored at 20–24 °C with constant gentle agitation to maintain pH and viability, and are licensed for 5 days. Bacterial surveillance methods may extend practice to 7 days in some settings, but the standard licensed interval is 5 days.

Question 5Blood Bank / Immunohematology

A newborn's red cells type as group A, but the plasma shows no anti-B. The most likely explanation is:

  1. The anti-B reagent has lost potency
  2. Maternal anti-B is blocking the reaction
  3. ABO antibodies are not fully developed in early infancy Correct answer.
  4. The infant has a weak subgroup of A

Explanation

Infants younger than about 4–6 months have not yet produced their own ABO antibodies, so reverse grouping is unreliable and typically not performed. Newborn typing relies on the forward (cell) grouping interpreted alongside the maternal ABO group.

Question 6Blood Bank / Immunohematology

Which testing method is used on all donated blood to detect HIV and HCV infection before seroconversion?

  1. Viral culture
  2. Nucleic acid testing Correct answer.
  3. Western blot
  4. Enzyme immunoassay

Explanation

Nucleic acid testing amplifies viral RNA or DNA and shortens the window period by detecting infection days to weeks before antibody appears. It is performed in minipools or by individual donation in addition to serologic screening.

Question 7Blood Bank / Immunohematology

A patient develops fever and chills 30 minutes into a red cell transfusion. The most appropriate immediate action is to:

  1. Give diphenhydramine and restart the same unit
  2. Slow the transfusion and give acetaminophen
  3. Continue the transfusion and observe closely
  4. Stop the transfusion and begin evaluation for a hemolytic reaction Correct answer.

Explanation

Any new fever or chills during transfusion is managed by stopping the transfusion and assessing for acute hemolysis, sepsis, or bacterial contamination. The transfusion service is notified and the unit and post-transfusion specimens are returned for investigation.

Question 8Blood Bank / Immunohematology

An eluate prepared from a patient's DAT-positive red cells reacts with every panel cell as well as the patient's own cells, and the autocontrol is positive. This pattern indicates:

  1. Passive anti-D from recent Rh immune globulin
  2. An alloantibody to a low-incidence antigen
  3. A high-titer cold agglutinin
  4. A warm autoantibody Correct answer.

Explanation

Panreactivity that includes the patient's own cells with a positive autocontrol points to an autoantibody, most often a warm IgG autoantibody. An alloantibody to a high-incidence antigen would not react with autologous cells, so the autocontrol helps make the distinction.

Question 9Blood Bank / Immunohematology

Which alloantibody classically binds complement, shows dosage, and may fall below the limit of detection, producing a delayed hemolytic transfusion reaction?

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

Explanation

Kidd antibodies are IgG that fix complement, react more strongly with homozygous cells, and often become undetectable over time. When anamnestic production resumes after transfusion, a delayed hemolytic reaction may occur.

Question 10Blood Bank / Immunohematology

A patient with a negative antibody screen and no history of clinically significant antibodies has an incompatible immediate-spin crossmatch. The most appropriate next step is to:

  1. Administer Rh immune globulin
  2. Substitute group AB plasma for the unit
  3. Investigate for ABO incompatibility and rouleaux Correct answer.
  4. Release the unit, because the antibody screen was negative

Explanation

With a negative screen and no antibody history, an incompatible immediate-spin crossmatch usually reflects ABO incompatibility, clerical error, or rouleaux rather than an unexpected antibody. The unit is withheld while ABO typings are repeated and saline replacement is used to resolve rouleaux.

Question 11Blood Bank / Immunohematology

An Rh-negative woman with a negative antibody screen is 28 weeks pregnant. Which management is appropriate?

  1. Antenatal Rh immune globulin at about 28 weeks plus a postpartum dose if the infant is Rh positive Correct answer.
  2. Rh immune globulin only after delivery, regardless of the infant's type
  3. Rh immune globulin only if the father is known to be Rh positive
  4. No Rh immune globulin because the antibody screen is negative

Explanation

Routine antenatal prophylaxis at approximately 28 weeks plus a postpartum dose given within 72 hours of delivery of an Rh-positive infant reduces the risk of D alloimmunization. A negative antibody screen confirms the mother is still a candidate for prophylaxis.

Question 12Blood Bank / Immunohematology

Cellular blood components are irradiated to prevent:

  1. Citrate toxicity
  2. Volume overload
  3. Febrile nonhemolytic reactions
  4. Transfusion-associated graft-versus-host disease Correct answer.

Explanation

Irradiation inactivates the DNA of passenger T lymphocytes, preventing their engraftment and proliferation in an immunocompromised recipient. This prevents transfusion-associated graft-versus-host disease, which is nearly always fatal.

Question 13Blood Bank / Immunohematology

Which statement best describes Lewis antibodies?

  1. Warm-reactive alloantibodies requiring antigen-negative units for every patient
  2. Complement-fixing IgG antibodies associated with delayed hemolytic reactions
  3. Naturally occurring IgM antibodies that are usually clinically insignificant and do not cause HDN Correct answer.
  4. IgG antibodies that cross the placenta and cause severe HDN

Explanation

Lewis antibodies are naturally occurring IgM that react optimally at room temperature and do not cross the placenta, so they do not cause hemolytic disease of the newborn. They are generally not clinically significant, and Lewis antigens are also soluble in plasma, which can neutralize the antibody.

Question 14Blood Bank / Immunohematology

A patient with congestive heart failure develops dyspnea, orthopnea, and hypertension during a two-unit red cell transfusion and improves after diuretic therapy. The most likely diagnosis is:

  1. Transfusion-associated circulatory overload Correct answer.
  2. Febrile nonhemolytic reaction
  3. Anaphylactic reaction
  4. Transfusion-related acute lung injury

Explanation

Volume overload produces dyspnea, hypertension, jugular venous distention, and elevated natriuretic peptide, and it responds to diuresis. TRALI instead presents with fever, hypotension, and bilateral infiltrates without volume overload.

Question 15Blood Bank / Immunohematology

Anti-A1 found in the serum of a group A2 individual is best described as:

  1. IgG that causes hemolytic disease of the newborn
  2. Absent from all group A2 individuals
  3. A naturally occurring IgM of no clinical significance Correct answer.
  4. Complement-fixing IgG causing acute hemolysis

Explanation

About 1–8% of A2 and 22–35% of A2B individuals produce anti-A1, a naturally occurring IgM that reacts at or below room temperature. It is generally clinically insignificant, and A2 cells are compatible with A2 recipients.

Question 16Blood Bank / Immunohematology

A patient's current antibody screen is negative, but records show a prior anti-Jkᵃ. What is required for transfusion?

  1. Select Jk(a−) units and perform an AHG crossmatch Correct answer.
  2. No further action, because the negative screen excludes the antibody
  3. Wash the units with saline before transfusion
  4. Only an immediate-spin crossmatch is required

Explanation

A previously identified antibody may have fallen below the limit of detection while remaining capable of an anamnestic response. The patient must receive antigen-negative units and a full antiglobulin crossmatch rather than an immediate-spin crossmatch.

Question 17Blood Bank / Immunohematology

A patient undergoing a large-volume plasma exchange develops perioral tingling, tremor, and carpopedal spasm. The most likely cause is:

  1. Metabolic alkalosis from lactate metabolism
  2. Hypocalcemia from the citrate anticoagulant Correct answer.
  3. Hypoglycemia from fasting
  4. Hyperkalemia from stored red cells

Explanation

Citrate chelates ionized calcium, and rapid infusion or exchange can produce hypocalcemia with paresthesias, tremor, and tetany. Symptoms are treated by slowing the procedure or giving intravenous calcium.

Question 18Blood Bank / Immunohematology

A donor unit is nonreactive with anti-D at immediate spin but reactive in the antiglobulin phase. How should the unit be labeled?

  1. D-negative
  2. D-negative with a comment
  3. D-unable to determine
  4. D-positive Correct answer.

Explanation

A donor unit is labeled D-positive if any D test is reactive, including weak D detected only by the antiglobulin technique. This prevents D-negative recipients from being exposed to weakly D-positive red cells, which can stimulate anti-D.

Question 19Blood Bank / Immunohematology

A patient with IgA deficiency and a history of anaphylaxis to blood products requires red cells. The most appropriate product is:

  1. Group AB fresh frozen plasma
  2. Washed red cells from an IgA-deficient donor Correct answer.
  3. Pooled platelets suspended in plasma
  4. Whole blood from a random donor

Explanation

Patients with anti-IgA can react to IgA in donor plasma, so cellular components should be washed and, when available, obtained from an IgA-deficient donor. Plasma-containing components are avoided or must also come from IgA-deficient donors.

Question 20Blood Bank / Immunohematology

A patient's serum spontaneously agglutinates at immediate spin, and the autocontrol is also positive. Reactivity is stronger at 4 °C and disappears at 37 °C. This pattern indicates:

  1. A cold-reacting autoantibody such as anti-I Correct answer.
  2. A warm autoantibody
  3. An anti-D alloantibody
  4. Rouleaux formation

Explanation

Reactivity at room temperature that intensifies in the cold and disperses at 37 °C is characteristic of a cold autoagglutinin, most often anti-I. Rouleaux, in contrast, is dispersed by saline replacement rather than by warming.

Question 21Blood Bank / Immunohematology

A patient qualifies for an electronic (computer) crossmatch when the record shows:

  1. Concordant ABO typings and a negative screen with no antibody history Correct answer.
  2. An antibody screen that is positive while the autocontrol is negative
  3. A history of anti-K with a currently negative antibody screen
  4. No ABO typing on file from any previous encounter

Explanation

Electronic crossmatching requires two concordant ABO determinations, a currently negative antibody screen, no history of clinically significant antibodies, and a validated computer system. Any positive screen or antibody history mandates a serologic crossmatch.

Question 22Blood Bank / Immunohematology

Treatment of reagent panel cells with ficin destroys which of the following antigens?

  1. D
  2. Jkᵃ
  3. Fyᵃ Correct answer.
  4. K

Explanation

Proteolytic enzymes such as ficin and papain destroy the Duffy antigens Fyᵃ and Fyᵇ along with some MNS antigens, while enhancing Rh, Kidd, and Lewis reactivity. Loss of reactivity after enzyme treatment is therefore useful in antibody identification.

Question 23Blood Bank / Immunohematology

A patient develops fever, chills, and dark urine shortly after a red cell transfusion. Which set of investigations is most appropriate?

  1. Clerical check, DAT, and repeat ABO/Rh on a post-transfusion sample Correct answer.
  2. Culture the blood bag and the patient's tubing
  3. Repeat the antibody screen the following day only
  4. Repeat the same unit at a slower rate after premedication

Explanation

Suspected acute hemolysis requires an immediate clerical check, visual comparison of pre- and post-transfusion specimens for hemolysis, a DAT, and repeat ABO/Rh typing. These steps rapidly identify the most common cause, ABO-incompatible transfusion from misidentification.

Question 24Blood Bank / Immunohematology

Anti-human globulin reagent must be quality controlled on each day of use with:

  1. Pooled group O cells incubated at 37 °C
  2. IgG-sensitized and unsensitized red cells Correct answer.
  3. A1, B, and O reagent cells
  4. Cord cells only

Explanation

Daily quality control of anti-human globulin confirms both that the reagent reacts with IgG-coated cells (potency) and that it does not agglutinate unsensitized cells (absence of nonspecific activity). The unsensitized cells also verify that the reagent contains anti-human globulin rather than only anti-complement.

Question 25Clinical Chemistry

Which biomarker is the preferred indicator of myocardial injury because of its high cardiac specificity?

  1. Cardiac troponin I Correct answer.
  2. Lactate dehydrogenase
  3. Creatine kinase MB
  4. Myoglobin

Explanation

Troponin I and T are expressed only in myocardium, so their release is highly specific for myocardial injury; they rise within a few hours and stay elevated for 7 to 14 days.

Question 26Clinical Chemistry

Hemoglobin A1c reflects average blood glucose over approximately what period of time?

  1. 24 hours
  2. 7 days
  3. 12 months
  4. 2 to 3 months Correct answer.

Explanation

Glucose binds irreversibly to hemoglobin for the lifespan of the erythrocyte, so HbA1c averages glycemia over roughly 2 to 3 months, with the most recent 4 weeks weighted most heavily.

Question 27Clinical Chemistry

A patient reports fatigue and weight gain. Results are TSH 22 mIU/L (reference 0.4 to 4.0) and a low free T4. Which pattern does this represent?

  1. Secondary hypothyroidism
  2. Primary hypothyroidism Correct answer.
  3. Euthyroid sick syndrome
  4. Subclinical hyperthyroidism

Explanation

A high TSH together with a low free T4 shows that the pituitary is responding normally to a failing thyroid gland, which defines primary hypothyroidism.

Question 28Clinical Chemistry

Which enzyme is considered the most liver-specific aminotransferase?

  1. Alanine aminotransferase Correct answer.
  2. Gamma-glutamyl transferase
  3. Aspartate aminotransferase
  4. Alkaline phosphatase

Explanation

ALT is confined largely to hepatocyte cytosol, whereas AST also occurs in cardiac and skeletal muscle and in erythrocytes; alkaline phosphatase and GGT are not aminotransferases.

Question 29Clinical Chemistry

A visibly hemolyzed serum specimen gives a potassium of 6.8 mmol/L, while the patient's previous result was 4.1 mmol/L. What is the most likely explanation?

  1. Contamination with EDTA
  2. True hyperkalemia from renal failure
  3. Potassium released from lysed red cells Correct answer.
  4. Analytical drift in the ion-selective electrode

Explanation

Erythrocytes contain potassium at roughly 25 times the plasma concentration, so hemolysis releases enough intracellular potassium to raise the measured value substantially.

Question 30Clinical Chemistry

Which laboratory test is most specific for acute pancreatitis?

  1. Alkaline phosphatase
  2. Total amylase
  3. Creatine kinase
  4. Lipase Correct answer.

Explanation

Lipase is produced almost exclusively by the pancreas, so it is more specific than amylase, which also comes from salivary glands and other tissues, and it remains elevated longer.

Question 31Clinical Chemistry

Which analyte is the predominant cation of extracellular fluid and the largest contributor to serum osmolality?

  1. Potassium
  2. Calcium
  3. Magnesium
  4. Sodium Correct answer.

Explanation

Sodium accounts for about 90 percent of extracellular cations, and the calculated osmolality formula doubles the sodium concentration to reflect its dominant osmotic contribution.

Question 32Clinical Chemistry

According to the American Diabetes Association, a fasting plasma glucose at or above which value is diagnostic of diabetes mellitus?

  1. 110 mg/dL
  2. 126 mg/dL Correct answer.
  3. 100 mg/dL
  4. 120 mg/dL

Explanation

A fasting plasma glucose of 126 mg/dL or greater, confirmed on a second occasion, meets the diagnostic threshold; values from 100 to 125 mg/dL define impaired fasting glucose.

Question 33Clinical Chemistry

A patient has sodium 140 mmol/L, chloride 100 mmol/L, and bicarbonate 14 mmol/L. What is the anion gap?

  1. 26 mmol/L Correct answer.
  2. 40 mmol/L
  3. 14 mmol/L
  4. 18 mmol/L

Explanation

Anion gap equals sodium minus the sum of chloride and bicarbonate: 140 minus 114 equals 26 mmol/L, which is well above reference limits and indicates a high-anion-gap metabolic acidosis.

Question 34Clinical Chemistry

Measured serum osmolality is 320 mOsm/kg while the calculated value (2 Na + glucose/18 + BUN/2.8) is 290 mOsm/kg. Which condition best explains an osmolal gap of 30?

  1. Lactic acidosis
  2. Methanol ingestion Correct answer.
  3. Diabetic ketoacidosis
  4. Uremia

Explanation

An osmolal gap above about 10 mOsm/kg implies an unmeasured low-molecular-weight solute; methanol and ethylene glycol are classic causes, since the calculated formula accounts only for sodium, glucose, and urea.

Question 35Clinical Chemistry

A patient with marked hypertriglyceridemia has a sodium of 118 mmol/L by indirect ion-selective electrode but 140 mmol/L by direct ISE on a blood gas analyzer. What accounts for the difference?

  1. Pseudohyponatremia Correct answer.
  2. SIADH
  3. Blood gas analyzer imprecision
  4. Excessive renal sodium loss

Explanation

Indirect ISE dilutes whole plasma and reports sodium per volume of plasma, so a large lipid volume displaces plasma water and falsely lowers the result; direct ISE measures undiluted whole blood and gives the true value.

Question 36Clinical Chemistry

A dehydrated patient has BUN 42 mg/dL and creatinine 1.2 mg/dL, a ratio near 35:1, with an unremarkable urinalysis. What is the most likely cause?

  1. Chronic kidney disease
  2. Gastrointestinal bleeding
  3. Acute tubular necrosis
  4. Prerenal azotemia Correct answer.

Explanation

In volume depletion, proximal tubular urea reabsorption increases while creatinine is not reabsorbed, so the BUN-to-creatinine ratio rises above 20:1; an unremarkable urinalysis argues against intrinsic renal disease.

Question 37Clinical Chemistry

Total cholesterol is 250 mg/dL, HDL cholesterol is 50 mg/dL, and triglycerides are 150 mg/dL. What is the LDL cholesterol by the Friedewald formula?

  1. 150 mg/dL
  2. 200 mg/dL
  3. 170 mg/dL Correct answer.
  4. 120 mg/dL

Explanation

Friedewald calculates LDL as total cholesterol minus HDL minus triglycerides divided by 5: 250 minus 50 minus 30 equals 170 mg/dL, a formula valid only when triglycerides are below 400 mg/dL.

Question 38Clinical Chemistry

A newborn has a total bilirubin of 14 mg/dL with a direct (conjugated) fraction of 0.4 mg/dL. Which condition best fits this pattern?

  1. Extrahepatic biliary obstruction
  2. Acute viral hepatitis
  3. Physiologic neonatal jaundice Correct answer.
  4. Dubin-Johnson syndrome

Explanation

A direct fraction under roughly 20 percent of total bilirubin indicates unconjugated hyperbilirubinemia; immature hepatic glucuronyl transferase plus a large neonatal bilirubin load produce this physiologic pattern.

Question 39Clinical Chemistry

A patient has an isolated elevation of alkaline phosphatase. Which additional test best distinguishes a hepatic from a skeletal source?

  1. Prothrombin time
  2. GGT Correct answer.
  3. Alanine aminotransferase
  4. Serum albumin

Explanation

GGT is present in hepatobiliary tissue but not in bone, so an elevated GGT alongside a high ALP confirms a hepatic origin, while a normal GGT points toward bone.

Question 40Clinical Chemistry

A dense, narrow band in the gamma region on serum protein electrophoresis indicates which of the following?

  1. Alpha-1 antitrypsin deficiency
  2. Monoclonal gammopathy Correct answer.
  3. Nephrotic syndrome
  4. Polyclonal hypergammaglobulinemia

Explanation

A restricted, sharp band arises when a single clone of plasma cells secretes a homogeneous immunoglobulin, whereas a broad smooth gamma rise reflects a polyclonal response.

Question 41Clinical Chemistry

For a conventional vancomycin dosing regimen, when should a serum trough level be collected?

  1. One hour after the end of the infusion
  2. Two hours after the first dose
  3. At any point in the dosing interval
  4. Within 30 minutes before the next dose Correct answer.

Explanation

A trough is drawn just before the next scheduled dose, when distribution is complete and the concentration is at its lowest, so it can be compared with the target trough range.

Question 42Clinical Chemistry

Which set of iron studies is typical of uncomplicated iron deficiency anemia?

  1. High ferritin with high transferrin saturation
  2. Low ferritin with high TIBC Correct answer.
  3. High ferritin with low TIBC
  4. Normal ferritin with low TIBC

Explanation

Iron deficiency depletes storage iron so ferritin falls, while hepatic transferrin synthesis increases, raising TIBC and dropping transferrin saturation below about 20 percent.

Question 43Clinical Chemistry

A patient with fever and neck stiffness has a CSF glucose of 25 mg/dL with a simultaneous serum glucose of 100 mg/dL. Which interpretation is correct?

  1. A ratio typical of bacterial meningitis Correct answer.
  2. Normal CSF-to-serum glucose ratio
  3. A ratio typical of viral meningitis
  4. A ratio typical of Guillain-Barré syndrome

Explanation

CSF glucose is normally about 60 percent of serum glucose; a ratio of 0.25 with a low absolute CSF glucose is characteristic of bacterial or fungal meningitis, in which organisms and neutrophils consume glucose.

Question 44Clinical Chemistry

A 24-hour urine collection of 1440 mL has a urine creatinine of 100 mg/dL and the serum creatinine is 1.0 mg/dL. What is the creatinine clearance?

  1. 72 mL/min
  2. 144 mL/min
  3. 50 mL/min
  4. 100 mL/min Correct answer.

Explanation

Clearance equals urine creatinine times urine volume divided by serum creatinine times collection time in minutes: (100 mg/dL x 1440 mL) divided by (1.0 mg/dL x 1440 min) equals 100 mL/min, since the 1440 mL collected over 1440 minutes equals 1 mL/min.

Question 45Clinical Chemistry

A single control measurement exceeds the mean by 3.2 SD while the other control level remains within limits. Which Westgard rule is violated?

  1. 4:1s
  2. 2:2s
  3. 1:3s Correct answer.
  4. 10x

Explanation

The 1:3s rule is violated when one control result falls beyond 3 SD from the mean and is a rejection rule primarily associated with random error.

Question 46Clinical Chemistry

A patient presents 5 hours after a single intentional acetaminophen overdose. Which result best guides the decision to begin N-acetylcysteine?

  1. Acetaminophen concentration on the nomogram Correct answer.
  2. Serum ALT measured at presentation
  3. Urine immunoassay screen for acetaminophen
  4. Prothrombin time

Explanation

For a single acute ingestion with a known time, the serum acetaminophen concentration plotted against time on the Rumack-Matthew nomogram determines whether treatment is indicated, because hepatic injury markers lag behind the exposure.

Question 47Clinical Chemistry

A patient with macrocytic anemia has a serum B12 within the reference interval but elevated methylmalonic acid and elevated homocysteine. What is the best interpretation?

  1. An inborn error of methionine metabolism is likely
  2. Functional B12 deficiency at the tissue level Correct answer.
  3. Serum B12 is normal, so B12 deficiency is excluded
  4. The results are diagnostic of alcoholism

Explanation

Methylmalonic acid rises specifically when tissue B12 is inadequate, so an elevated methylmalonic acid with elevated homocysteine can reveal functional deficiency while total serum B12 is still within reference limits.

Question 48Clinical Chemistry

A specimen shows potassium 7.2 mmol/L, calcium 1.9 mmol/L, and magnesium 1.2 mmol/L in a patient with no symptoms. Which preanalytical problem best explains this combination?

  1. Delayed separation of serum from cells
  2. EDTA carryover from a lavender-top tube Correct answer.
  3. Prolonged tourniquet application with fist clenching
  4. Hemolysis of the specimen

Explanation

EDTA is a potassium salt that chelates divalent cations, so carryover produces spuriously high potassium together with low calcium and low magnesium, a combination that is the signature of this contamination.

Question 49Clinical Chemistry

A patient has pH 7.30, PCO2 30 mmHg, bicarbonate 15 mmol/L, sodium 140 mmol/L, and chloride 95 mmol/L. Which statement best describes the acid-base status?

  1. High anion gap acidosis plus metabolic alkalosis Correct answer.
  2. High anion gap acidosis with a respiratory acidosis
  3. Simple high anion gap metabolic acidosis alone
  4. Mixed respiratory acidosis and metabolic alkalosis

Explanation

The anion gap is 140 minus 110, or 30, and the delta ratio is (30 minus 12) divided by (24 minus 15), or 2.0; a ratio above 1 means bicarbonate fell less than the anion gap rose, so a metabolic alkalosis coexists with the high-anion-gap acidosis.

Question 50Clinical Chemistry

A woman in the second trimester of pregnancy has a total T4 of 14.5 µg/dL (reference interval 5.0–12.0), a free T4 within the reference interval, and a TSH of 1.8 mIU/L. Which finding best accounts for these results?

  1. An estrogen-driven rise in binding globulin Correct answer.
  2. Dietary iodine deficiency
  3. Early primary hypothyroidism
  4. A fall in thyroid hormone–binding globulin

Explanation

Estrogen in pregnancy stimulates hepatic synthesis of thyroid hormone–binding globulin, so the bound and therefore total T4 pool expands while the free (biologically active) fraction stays normal. Because free T4 is unchanged, TSH remains within reference limits and the patient is euthyroid. Total T4 results in pregnancy must therefore be interpreted against trimester-specific or pregnancy-adjusted ranges.