Faculty tips and pearls for diagnostic tests

MD 2 Cardiopulmonary Diagnostic Tests

• CXR for diagnosing lower respiratory tract infections in the community

Chest X-ray sensitivity: 75% (95% CI 54%-88%); specificity: 75% (95% CI 42%-92%) The majority of studies (86%) were performed in adults (78%), emergency departments (92%) and in European countries.  The comparator was CT scan of chest.

Gentilotti E, De Nardo P, Cremonini E et. al.  Diagnostic accuracy of point-of-care tests in acute community-acquired lower respiratory tract infections. A systematic review and meta-analysis. Clin Microbiol Infect. 2022 Jan;28(1):13-22. doi: 10.1016/j.cmi.2021.09.025. 

MD 3 Heme and Renal Diagnostic Tests

• Serum Cystatin C is an accurate estimation on eGFR in patients with or at risk for Chronic Kidney Disease

eGFRcr is the initial equation recommended for estimation of GFRa; its accuracy may be affected by muscle mass, diet, frailty, advanced heart failure or liver failure, and medications: trimethoprim, dronedarone, and tyrosine kinase inhibitors.

 eGFRcys may underestimate actual GFR in people who smoke cigarettes, with obesity, with hypothyroidism, or who take systemic corticosteroids. In these individuals, eGFRcr-cys typically provides the most accurate estimate of GFR.

Shlipak MG, Inker LA, Coresh J. Serum Cystatin C for Estimation of GFR. JAMA. 2022;328(9):883–884. doi:10.1001/jama.2022.12407

• 24-h urine magnesium level for Mg++ wasting differentiates renal from non-renal causes

A urinary magnesium test (24 h collection assesses polyuria also) differentiates between renal and non-renal causes of magnesium wasting.  Hypomagnesemia secondary to glycosuria-induced polyuria improves with glycemic control.

Tucker BM, Pirkle JL, Raghavan R. Urinary Magnesium in the Evaluation of Hypomagnesemia. JAMA. 2020;324(22):2320–2321. doi:10.1001/jama.2020.18400

MD 4 Endocrine and Gastrointestinal Diagnostic Tests

• Clostridioides difficile multi-step testing algorithms

Multistep CDI test algorithms consist of a sensitive stool screening test, such as a nucleic acid amplification test (NAAT) [96%] or glutamate dehydrogenase (GDH) antigen testing, and a specific test, enzyme immunoassay (EIA) [99%] for C difficile toxin A and B.  Multistep CDI testing may help distinguish CDI from colonization, potentially avoiding unnecessary antibiotics.  Patients with a positive NAAT or GDH antigen test and a negative toxin EIA result may have symptomatic CDI or may be asymptomatic carriers of C difficile.  Pre-test probability and clinical context should determine care.

Nicholson MR, Donskey CJ. Multistep Testing Algorithms for Clostridioides difficile Infection. JAMA. 2023;330(10):966–967. doi:10.1001/jama.2023.15875

• FIBROSCAN (VCTE) is diagnostic test for cirrhosis

Vibration-Controlled Transient Elastography for Diagnosing Cirrhosis & Staging Hepatic Fibrosis

Vibration-controlled transient elastography (VCTE) accurately confirms the presence or absence of cirrhosis in many etiologies of chronic liver disease.  Liver stiffness measurement (LSM) should be interpreted within the clinical context for each patient, and results should be corroborated with other noninvasive tests or liver biopsy if questions persist regarding LSM accuracy.  Clinicians must be aware of the limitations of VCTE in order to use and interpret results correctly.

Wilder J, Choi SS, Moylan CA. Vibration-Controlled Transient Elastography for Diagnosing Cirrhosis and Staging Hepatic Fibrosis. JAMA. 2018;320(19):2031–2032. doi:10.1001/jama.2018.13073 

• Hepatitis C RNA tests are 96-98% sensitive and 98-99% specific for diagnosis of infection.

Any patient with known risk factors for HCV or born between 1945 and 1965 should be screened for HCV.  Enzyme immunoassays for anti-HCV are used to screen for HCV infection and are very sensitive and specific.  A patient with a positive anti-HCV should have an HCV RNA tested to determine whether there is ongoing infection. 

Konerman MA, Lok AS. Diagnostic Challenges of Hepatitis C. JAMA : the journal of the American Medical Association. 2014;311(24):2536-2537. doi:10.1001/jama.2014.306

MD 6 Musculoskeletal, Neurological and Behavioral Diagnostic Tests

• Hip X-ray for diagnosis of fracture

The sensitivity of plain x-rays in detecting hip fracture is 90–98%, based on multiple studies. 

Heikal S, Riou P, Jones L. The use of computed tomography in identifying radiologically occult hip fractures in the elderly. Ann R Coll Surg Engl. 2014 Apr;96(3):234-7. doi: 10.1308/003588414X13824511650533

MD 7: LIFE CYCLE: Genitourinary, Reproductive, Pediatric and Geriatric Diagnostics

• Serum hCG test (and quantitative values) for diagnosis of pregnancy

Serum hCG testing should be considered in all patients with possible pregnancy given significant variability in hCG levels and their degradation products in urine.  Urine hCG can be falsely-negative during weeks 1-4 and 6-8 of gestation. Sensitivity is 90-97% for pregnancy.

Latifi N, Kriegel G, Herskovits AZ. Point-of-Care Urine Pregnancy Tests. JAMA. 2019;322(23):2336–2337. doi:10.1001/jama.2019.15833