Ordering tests US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Ordering tests. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Ordering tests US Medical PG Question 1: A researcher is trying to determine whether a newly discovered substance X can be useful in promoting wound healing after surgery. She conducts this study by enrolling the next 100 patients that will be undergoing this surgery and separating them into 2 groups. She decides which patient will be in which group by using a random number generator. Subsequently, she prepares 1 set of syringes with the novel substance X and 1 set of syringes with a saline control. Both of these sets of syringes are unlabeled and the substances inside cannot be distinguished. She gives the surgeon performing the surgery 1 of the syringes and does not inform him nor the patient which syringe was used. After the study is complete, she analyzes all the data that was collected and performs statistical analysis. This study most likely provides which level of evidence for use of substance X?
- A. Level 3
- B. Level 1 (Correct Answer)
- C. Level 4
- D. Level 5
- E. Level 2
Ordering tests Explanation: ***Level 1***
- The study design described is a **randomized controlled trial (RCT)**, which is considered the **highest level of evidence (Level 1)** in the hierarchy of medical evidence.
- Key features like **randomization**, **control group**, and **blinding (double-blind)** help minimize bias and strengthen the validity of the findings.
*Level 2*
- Level 2 evidence typically comprises **well-designed controlled trials without randomization** (non-randomized controlled trials) or **high-quality cohort studies**.
- While strong, they do not possess the same level of internal validity as randomized controlled trials.
*Level 3*
- Level 3 evidence typically includes **case-control studies** or **cohort studies**, which are observational designs and carry a higher risk of bias compared to RCTs.
- These studies generally do not involve randomization or intervention assignment by the researchers.
*Level 4*
- Level 4 evidence is usually derived from **case series** or **poor quality cohort and case-control studies**.
- These studies provide descriptive information or investigate associations without strong control for confounding factors.
*Level 5*
- Level 5 evidence is the **lowest level of evidence**, consisting of **expert opinion** or **animal research/bench research**.
- This level lacks human clinical data or systematic investigative rigor needed for higher evidence levels.
Ordering tests US Medical PG Question 2: A 26-year-old medical student comes to the physician with a 3-week history of night sweats and myalgias. During this time, he has also had a 3.6-kg (8-lb) weight loss. He returned from a 6-month tropical medicine rotation in Cambodia 1 month ago. A chest x-ray (CXR) shows reticulonodular opacities suggestive of active tuberculosis (TB). The student is curious about his likelihood of having active TB. He reads a study that compares sputum testing results between 2,800 patients with likely active TB on a basis of history, clinical symptoms, and CXR pattern and 2,400 controls. The results are shown:
Sputum testing positive for TB Sputum testing negative for TB Total
Active TB likely on basis of history, clinical symptoms, and CXR pattern 700 2100 2,800
Active TB not likely on basis of history, clinical symptoms, and CXR pattern 300 2100 2,400
Total 1000 4200 5,200
Which of the following values reflects the probability that a patient with a diagnosis of active TB on the basis of history, clinical symptoms, and CXR pattern actually has active TB?
- A. 1.4
- B. 0.50
- C. 0.70
- D. 0.88
- E. 0.25 (Correct Answer)
Ordering tests Explanation: ***0.25***
- This value represents the **positive predictive value (PPV)** for active TB based on the initial clinical assessment criteria (history, symptoms, CXR).
- PPV is calculated as the number of true positives (700) divided by the total number of individuals with a positive clinical diagnosis (700 + 2100 = 2800). So, 700 / 2800 = 0.25.
- **This answers the question**: the probability that someone with a clinical diagnosis of active TB actually has the disease.
*Incorrect 1.4*
- This value is not a valid probability, as probabilities must be between 0 and 1.0.
- It might arise from an incorrect calculation or misinterpretation of the provided data.
*Incorrect 0.50*
- This value does not correspond to any standard diagnostic metric calculated from the provided data.
- The actual prevalence of TB (based on positive sputum) is 1000/5200 = 0.19, not 0.50.
- This is likely a distractor with no meaningful interpretation in this context.
*Incorrect 0.70*
- This value represents the **sensitivity** of the sputum test for detecting active TB.
- Sensitivity is calculated as true positives (700) divided by total with disease (700 + 300 = 1000). So, 700 / 1000 = 0.70.
- Sensitivity tells us how good the test is at detecting disease when present, not the probability of having disease given a positive clinical diagnosis.
*Incorrect 0.88*
- This value represents the **specificity** of the clinical assessment.
- Specificity is calculated as true negatives (2100) divided by total without disease (2100 + 300 = 2400). So, 2100 / 2400 = 0.875 ≈ 0.88.
- Specificity tells us how good the assessment is at ruling out disease in those without it, not the probability of disease given a positive assessment.
Ordering tests US Medical PG Question 3: A 43-year-old woman presents to her primary care physician with complaints of mild shortness of breath and right-sided chest pain for three days. She reports that lately she has had a nagging nonproductive cough and low-grade fevers. On examination, her vital signs are: temperature 99.1 deg F (37.3 deg C), blood pressure is 115/70 mmHg, pulse is 91/min, respirations are 17/min, and oxygen saturation 97% on room air. She is well-appearing, with normal work of breathing, and no leg swelling. She is otherwise healthy, with no prior medical or surgical history, currently taking no medications. The attending has a low suspicion for the most concerning diagnosis and would like to exclude it with a very sensitive though non-specific test. Which of the following should this physician order?
- A. Obtain chest radiograph
- B. Obtain spiral CT chest with IV contrast
- C. Order a lower extremity ultrasound
- D. Order a D-dimer (Correct Answer)
- E. Obtain ventilation-perfusion scan
Ordering tests Explanation: ***Order a D-dimer***
- The physician has a **low suspicion based on clinical assessment** and wants to **exclude** a concerning diagnosis (likely **pulmonary embolism** or PE) using a **sensitive test**. A negative D-dimer test can effectively rule out PE in patients with a low pre-test probability.
- The D-dimer is a product of **fibrin degradation** and its elevation indicates recent or ongoing **thrombus formation** and lysis. It is highly sensitive for PE but has low specificity.
*Obtain chest radiograph*
- A chest radiograph is often **normal in pulmonary embolism** or may show non-specific findings, making it unsuitable for ruling out PE.
- While useful for diagnosing other conditions like pneumonia or pleural effusions, it is **not sensitive enough to exclude PE**.
*Obtain spiral CT chest with IV contrast*
- A **spiral CT chest with IV contrast (CT pulmonary angiography)** is the gold standard for diagnosing PE, but it is **not a sensitive rule-out test** for low-probability cases.
- It involves **radiation exposure** and **contrast administration**, which are generally avoided if a less invasive, equally effective rule-out test is available for low-risk patients.
*Order a lower extremity ultrasound*
- Lower extremity ultrasound is used to diagnose **deep vein thrombosis (DVT)**, which is a common source of PE.
- While DVT can lead to PE, a negative lower extremity ultrasound **does not rule out PE** itself, as the clot may have already embolized or originated from elsewhere.
*Obtain ventilation-perfusion scan*
- A **ventilation-perfusion (V/Q) scan** is an alternative to CT angiography for diagnosing PE, particularly in patients with contraindications to contrast.
- However, it is **less definitive than CTPA** and is typically used when suspicion for PE is moderate or higher, rather than as a primary rule-out test for low-probability patients.
Ordering tests US Medical PG Question 4: A 27-year-old man interested in pre-exposure therapy for HIV (PrEP) is being evaluated to qualify for a PrEP study. In order to qualify, patients must be HIV- and hepatitis B- and C-negative. Any other sexually transmitted infections require treatment prior to initiation of PrEP. The medical history is positive for a prior syphilis infection and bipolar affective disorder, for which he takes lithium. On his next visit, the liver and renal enzymes are within normal ranges. HIV and hepatitis B and C tests are negative. Which of the following about the HIV test is true?
- A. It is a quantitative test used for screening purposes.
- B. It is a qualitative test used for screening purposes. (Correct Answer)
- C. A secondary reagent is needed to interpret the results.
- D. A known antigen binds directly to the patient's serum.
- E. An unknown antigen binds to the known serum.
Ordering tests Explanation: ***It is a qualitative test used for screening purposes.***
- **HIV screening tests** (e.g., 4th generation antibody/antigen combination assays) are typically **qualitative**, meaning they detect the presence or absence of HIV markers, not their exact amount.
- These tests are primarily used for broad **screening** of populations to identify potential cases of HIV infection.
*It is a quantitative test used for screening purposes.*
- **Quantitative tests** for HIV, such as viral load tests, measure the amount of virus in the blood and are typically used for monitoring disease progression or treatment effectiveness, not for initial screening.
- Screening tests are designed for high sensitivity to detect infection, even with low viral loads or early antibody responses, making a quantitative measurement less relevant for initial screening.
*A secondary reagent is needed to interpret the results.*
- While some complex immunoassays might involve multiple steps, modern **HIV screening tests** often use advanced technologies that directly yield results, making a separate secondary reagent for interpretation generally unnecessary.
- The results are typically indicated by a color change or a signal detected by an instrument, without requiring an additional interpretive reagent.
*A known antigen binds directly to the patient's serum.*
- **HIV antibody tests** detect **antibodies** produced by the patient's immune system in response to HIV infection.
- In such tests, **known HIV antigens** (from the test kit) bind to **HIV-specific antibodies present in the patient's serum**, not to serum components directly.
- This option is incorrect because it omits the critical role of antibodies as the target molecules being detected.
*An unknown antigen binds to the known serum.*
- This statement describes a different type of immunological assay where an unknown antigen is being identified using a known antibody, which is contrary to how **HIV screening tests** for infection are typically structured.
- **HIV screening tests** use known components (e.g., HIV antigens or antibodies) in the test kit to detect unknown components (e.g., HIV antibodies or viral antigens) in the patient's sample.
Ordering tests US Medical PG Question 5: A 27-year-old woman presents with acute abdominal pain in her right upper quadrant. The pain came on suddenly while she was eating dinner. After this pain she began feeling dizzy and came to the emergency department. In the ED, her blood pressure is 75/40 mmHg, pulse is 100/minute, and she is afebrile. On physical exam, she feels too light-headed to ambulate. She demonstrates normal bowel sounds with tenderness upon palpation in the right upper quadrant. The patient is deemed too unstable for imaging. An abdominal radiograph and CT are reviewed from a recent previous visit to the ED for mild abdominal pain, and are shown in Figures A and B, respectively. Which of the following specific additional findings in her history supports the most likely diagnosis?
- A. Symptoms that began after a fatty meal
- B. Use of oral contraceptives (OCPs) for birth control (Correct Answer)
- C. A 15 pack/year history of smoking
- D. A history of Epstein-Barr virus and participation in rugby
- E. An extensive history of sexually transmitted diseases (STDs) and pelvic inflammatory disease (PID)
Ordering tests Explanation: ***Use of oral contraceptives (OCPs) for birth control***
- The patient's presentation with acute right upper quadrant pain, **hemodynamic instability** (BP 75/40 mmHg, pulse 100/minute, dizziness), and previous imaging showing a hepatic lesion (implied by the question context though images aren't provided) strongly suggests a ruptured **hepatic adenoma**.
- **Oral contraceptive pill (OCP) use** is a well-established risk factor for the development and rupture of hepatic adenomas due to their estrogen content, which promotes growth.
*Symptoms that began after a fatty meal*
- Acute right upper quadrant pain exacerbated by a **fatty meal** is classic for **cholecystitis** or **biliary colic**.
- However, the patient's **hemodynamic instability** is not typical for uncomplicated cholecystitis, and hepatic adenoma rupture is a more fitting explanation for the sudden onset of profound shock.
*A 15 pack/year history of smoking*
- Smoking is a risk factor for various abdominal conditions, including **peptic ulcer disease** and certain **malignancies**.
- It is not a direct risk factor for **hepatic adenoma rupture** and does not explain the acute, life-threatening presentation in this young woman as well as OCP use.
*A history of Epstein-Barr virus and participation in rugby*
- A history of Epstein-Barr virus (EBV) and contact sports like rugby is associated with an increased risk of **splenic rupture**, especially if splenomegaly is present.
- While splenic rupture can cause acute abdominal pain and hypovolemic shock, the pain would typically be in the **left upper quadrant**, not the right.
*An extensive history of sexually transmitted diseases (STDs) and pelvic inflammatory disease (PID)*
- STDs and PID are risk factors for **ectopic pregnancy** (which can cause acute abdominal pain and rupture, leading to shock) and **Fitz-Hugh-Curtis syndrome** (perihepatitis causing RUQ pain).
- However, the patient's age and sex would make these considerations relevant, but the specific localization of pain to the right upper quadrant and the strong association with OCPs point more directly to a hepatic pathology.
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