MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 20
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
A multiply transfused patient of African descent has an antibody to a high-prevalence antigen. Her cells are S−s−. The most likely antibody is:
The S−s−U− phenotype occurs almost only in people of African descent, and these people can make clinically significant anti-U. Compatible blood must be U-negative, which is rare.
A pregnant woman who was Le(a−b+) now types Le(a−b−) and has weak anti-Leb. The best explanation is:
In pregnancy, increased plasma volume and lipoproteins take Lewis glycolipids off red cells, so antigens weaken and transient Lewis antibodies can appear. The type returns to normal after delivery.
Which appearance is typical of Lutheran antibodies such as anti-Lua?
Lutheran antibodies classically give loose, refractile, mixed-field agglutination with small clumps among many free cells. This reflects the variable Lutheran antigen expression on individual cells.
The Diego antigen Di(a) is found mainly in which populations?
Di(a) is carried on band 3 and is common in Indigenous peoples of the Americas and in East Asians but very rare in Europeans and Africans. Anti-Dia can cause HDFN.
Rh antibodies such as anti-D typically destroy red cells by which mechanism?
Rh antibodies are usually IgG and rarely activate complement. Coated cells are removed extravascularly, mainly in the spleen.
The Kleihauer-Betke test is based on the fact that fetal hemoglobin:
In acid buffer, adult hemoglobin leaches out, leaving ghost cells, while HbF-containing fetal cells stay pink after staining.
A transfusion reaction is reported. Which three checks form the initial laboratory investigation?
The immediate workup includes a clerical check of labels and records, inspection of post-transfusion plasma for free hemoglobin, and a DAT. Further tests are done only if these suggest hemolysis.
Which laboratory pattern best supports intravascular hemolysis after transfusion?
Free hemoglobin binds haptoglobin, which falls quickly; LDH rises from lysed cells and excess hemoglobin appears in urine. Haptoglobin is not increased during hemolysis.
Which finding meets the usual definition of a febrile non-hemolytic transfusion reaction?
FNHTR is a temperature of 38 °C or more with a rise of 1 °C or more during or soon after transfusion. It is a diagnosis of exclusion after hemolysis and sepsis are ruled out.
Which patient does NOT require irradiated cellular components?
Irradiation is indicated for intrauterine transfusion, Hodgkin lymphoma, purine analogue therapy and other high-risk settings. Routine surgical patients with normal immunity do not need it.
Hemoglobinuria follows a transfusion. Clerical check is correct, ABO types are compatible and the DAT is negative. The unit was warmed in a water bath at 50 °C. The cause is:
Heating red cells above the safe limit damages them and releases hemoglobin without any antibody. Blood must be warmed only with an approved, temperature-controlled device.
A patient with stable COPD has pH 7.36, pCO2 60 mmHg, HCO3− 33 mmol/L. This is best described as:
Raised pCO2 with pH at the low end of normal and markedly raised HCO3− indicates chronic respiratory acidosis compensated by renal bicarbonate retention. pH on the acid side points to the respiratory primary process.
Salicylate poisoning in an adult classically produces which early mixed disorder?
Salicylates stimulate the respiratory centre (respiratory alkalosis) and disturb metabolism, causing organic acid accumulation and a high anion gap metabolic acidosis.
Excess liquid heparin in a blood gas syringe most likely causes:
Liquid heparin has low pCO2 and dilutes the sample, lowering pCO2, bicarbonate and ionised calcium. Dry balanced heparin syringes are recommended.
In the Severinghaus pCO2 electrode, CO2 is detected because it:
CO2 crosses a gas-permeable membrane into a bicarbonate electrolyte, forming carbonic acid and changing pH, which a glass electrode measures. The Clark electrode uses reduction at platinum for pO2.
A patient given dapsone has chocolate-brown blood, normal pO2 and reduced oxygen saturation on co-oximetry. Which fraction is increased?
Oxidant drugs such as dapsone and local anaesthetics convert heme iron to Fe3+, forming methemoglobin, which cannot carry oxygen and gives brownish blood. Co-oximetry measures it at about 630 nm.
A glucose oxidase–peroxidase (Trinder) method gives falsely low results on a sample from a patient receiving high-dose vitamin C. Why?
Reducing substances such as ascorbic acid and uric acid consume hydrogen peroxide, so less coloured dye forms. The glucose oxidase step itself is not inhibited.
An adult has an HbA1c of 6.1% (43 mmol/mol). According to ADA, this result indicates:
HbA1c of 5.7–6.4% (39–47 mmol/mol) is the ADA prediabetes range. Diabetes needs 6.5% (48 mmol/mol) or higher.
In the two-step approach to gestational diabetes screening, the first step is:
The first step is a 50 g glucose challenge without fasting, with plasma glucose at 1 hour. Women above the cut-off then have the 100 g 3-hour OGTT.
HbA1c is formed by the non-enzymatic attachment of glucose to:
HbA1c is defined as hemoglobin with glucose bound as a stable ketoamine to the N-terminal valine of the beta chain. Glycated albumin is measured as fructosamine.