MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 23
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
The Henderson–Hasselbalch equation for the bicarbonate buffer system is:
pH = pKa (6.1) + log (bicarbonate / dissolved CO2), where dissolved CO2 = 0.0307 × pCO2 (mmHg) in mmol/L. Using 0.23 × pCO2 applies when pCO2 is in kPa.
pH 7.52, pCO2 48 mmHg, HCO3− 38 mmol/L. The most likely disorder is:
High pH with high HCO3− indicates primary metabolic alkalosis; the raised pCO2 reflects hypoventilation as compensation, and pH is still abnormal, so compensation is partial.
Type B lactic acidosis, occurring without tissue hypoxia, is associated with:
Type B lactic acidosis arises from impaired metabolism without poor perfusion, e.g. metformin, liver failure, thiamine deficiency or malignancy. Shock states cause type A (hypoxic) lactic acidosis.
A 48-year-old has a fasting plasma glucose of 112 mg/dL (6.2 mmol/L) and no symptoms. By ADA criteria this is:
Fasting glucose of 100–125 mg/dL (5.6–6.9 mmol/L) is impaired fasting glucose. Impaired glucose tolerance is defined by the 2-hour OGTT value, not the fasting value.
A patient with sickle cell disease needs monitoring of glycemic control. Which test is a suitable alternative to HbA1c?
Fructosamine measures glycated serum proteins (mainly albumin) and is not affected by red cell survival or Hb variants. C-peptide measures insulin secretion, not glycemic control.
A laboratory reports HbA1c in IFCC units. Which value corresponds to the ADA diabetes cut-off of 6.5%?
6.5% (NGSP/DCCT) equals 48 mmol/mol (IFCC). 39 mmol/mol equals 5.7%, the lower limit of prediabetes.
The nitroprusside reaction used in urine ketone strips reacts mainly with:
Nitroprusside reacts strongly with acetoacetate, weakly with acetone (if glycine is present), and not at all with beta-hydroxybutyrate. Lactate is not a ketone body.
Which antibodies support a diagnosis of autoimmune (type 1) diabetes?
Antibodies to GAD65, IA-2 (tyrosine phosphatase), ZnT8 and insulin mark beta-cell autoimmunity. Anti-TPO antibodies indicate autoimmune thyroid disease.
Albuminuria in a diabetic patient is confirmed when the urine albumin-to-creatinine ratio is at least:
Moderately increased albuminuria is ACR 30–299 mg/g, confirmed in at least 2 of 3 samples over 3–6 months because of day-to-day variation. One random sample is not enough.
A sample drawn above an IV line infusing 0.9% saline would show:
Contamination with normal saline increases chloride (and may keep or raise sodium) while diluting other analytes such as potassium, glucose, calcium and protein. Glucose would rise with dextrose infusion.
A patient with stage G5 chronic kidney disease typically shows:
Reduced phosphate excretion and low 1,25-dihydroxyvitamin D production lower calcium and raise phosphate, driving secondary hyperparathyroidism.
A patient with prolonged vomiting is most likely to show:
Loss of gastric HCl produces metabolic alkalosis with low chloride; volume depletion activates aldosterone, increasing renal potassium loss.
A critically ill ICU patient has low free T3, normal-to-low free T4 and normal TSH. The most likely interpretation is:
Severe illness reduces peripheral T4-to-T3 conversion and increases reverse T3. Thyroid tests are best not interpreted in acute illness unless dysfunction is strongly suspected.
After total thyroidectomy for differentiated thyroid cancer, thyroglobulin is used as a tumor marker. Which result must be checked with it?
Thyroglobulin antibodies can cause falsely low thyroglobulin results in immunometric assays, so they must be measured together. Calcitonin is the marker for medullary thyroid carcinoma.
In a short Synacthen (cosyntropin) stimulation test, a normal response is:
Synthetic ACTH should stimulate a normal adrenal to raise cortisol above a defined threshold (assay-dependent, often around 400–500 nmol/L). A poor response suggests adrenal insufficiency.
A woman with galactorrhoea has a very large pituitary mass but prolactin is only mildly raised. Which step should the lab take?
Very high prolactin can saturate both antibodies in a two-site immunoassay, giving a falsely low result (high-dose hook effect). Dilution reveals the true high concentration.
Total testosterone may be misleading in an obese man with low sex hormone-binding globulin (SHBG). The better assessment is:
Low SHBG lowers total testosterone without affecting free hormone. Free testosterone, calculated from total testosterone, SHBG and albumin, gives a better picture.
Enzyme activity assays are designed so that substrate is in large excess. Why?
With substrate in excess, the reaction follows zero-order kinetics, so the rate reflects enzyme concentration only. In first-order conditions the rate would vary with substrate concentration.
In the IFCC-type ALT method, pyruvate formed is reduced by lactate dehydrogenase. What is measured?
LD converts pyruvate to lactate while oxidizing NADH to NAD+; NADH absorbs at 340 nm, so absorbance falls at a rate proportional to ALT activity. The 405 nm reading applies to ALP methods.
A kinetic LD assay flags 'substrate depletion'; the absorbance change stops after the first readings. What should the technologist do?
Very high enzyme activity uses up the substrate early, so the rate is no longer linear and the result is falsely low. Diluting the sample and rerunning restores zero-order kinetics.