With input from Dr Monica Vasudev

1123: Most Popular COVID-19 Tests

US FDA has authorized around 230 diagnostic tests for COVID-19.

The tests are segregated as molecular versus antigen tests. Molecular tests identify viral RNA (often through PCR testing), while antigen tests detect viral surface proteins. Either of them can yield rapid tests, but antigen tests are faster.

Antigen tests are not as sensitive as molecular tests, and have a greater likelihood of false negatives.

Emergency use authorization for each antigen test points to use only in symptomatic patients.

Antigen tests are driving the point-of-care testing. Most of these tests require an instrument, but the machines are usually much smaller than PCR analyzers. Only the self-contained BinaxNOW (of the size of a credit card) doesnt need instrumentation. The Trump administration has purchased 150 million BinaxNOW tests from Abbott which are being distributed to schools and nursing homes. This was the test used at the White House when a super spreader event occurred there.

Molecular Tests

• Abbott IDNow: EUA; IFU; sensitivity/specificity: 100%/100%; results in 13 minutes
• Roche Cobas: EUA; IFU; sensitivity/specificity: 100%/100%; results in 3.5 hours
• Hologic Panther: EUA; IFU; sensitivity/specificity: 100%/100%; results in 3 hours
• Cepheid GeneXpert Xpress: EUA; IFU; sensitivity/specificity: 97.8%/95.6%; results in 45 minutes
• Thermo Fisher TaqPath: EUA; IFU; sensitivity/specificity: 100%/100%; results in 4 hours
• Labcorp: EUA; IFU; sensitivity/specificity: 100%/100%; results in 24 hours
• Quest Diagnostics: EUA; IFU; sensitivity/specificity: 100%/100%; results in 1 hour

Antigen Tests

• Abbott BinaxNOW: EUA; IFU; sensitivity/specificity: 97.1%/98.5%; results in 15 minutes
• Quidel Sofia: EUA; IFU; sensitivity/specificity: 96.7%/100%; results in 15 minutes
• BD Veritor: EUA; IFU; sensitivity/specificity: 84%/100%; results in 15 minutes
• Access Bio CareStart: EUA; IFU; sensitivity/specificity: 88.4%/100%; results in 10 minutes
• LumiraDx Ag: EUA; IFU; sensitivity/specificity: 97.6%/96.6%; results in 12 minutes

EUA = emergency use authorization

IFU = instructions for use.

[Source: Medpage Today]

1124: Thrombi and not emboli

1. There are high rates of venous thromboembolism, particularly pulmonary embolism, in hospitalized serious COVID-19 patients.
2. Thrombotic complications are seen in spite of the use of prophylactic, or at times, therapeutic anticoagulation.
3. COVID-19 patients have a risk for macro-thrombosis. They exhibit all three components of Virchow’s triad - stasis of blood flow, hypercoagulability, and endothelial injury.
4. Pathological reports suggest that they also have considerablemicro-thrombosis, or immuno-thrombosis, related to hypoxemia, endothelial injury, and inflammation.
5. Many cases of pulmonary embolism occur in the absence of DVT and are located in the more peripheral pulmonary arteries.
6. This phenotype is characterized by thrombi and not emboli, i.e., immuno-thrombosis.
7. A report of 66 patients in the ICU, who received standard-dose thromboprophylaxis, found only a 5% rate of VTE that was not thought to be either catheter-related thrombosis or immuno-thrombosis. Increased doses of anticoagulants may be ineffective in such cases, especially since larger doses are not recommended for other forms of microangiopathy.This could be the reason why some small reports found high rates of VTE even among patients who given full-dose anticoagulation. Upstream therapies, such as antiviral and immunomodulating agents, seem to have a role to reduce the development of immuno-thrombosis, and may prove more efficacious than downstream attempts to suppress the coagulation system.
8. Extended thromboprophylaxis would yield a net benefit only if the risk of symptomatic VTE is more than 1.8% after hospital discharge.

[NEJM.org.]

Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA