Total gross margin for full year 2021 was 36.0% compared to 38.0% in full year 2020. In the fourth quarter of 2021, our test strip margin exceeded 80% while overall fourth quarter 2021 gross margin improved to 46.1% compared to third quarter 2021 gross margin of 35.6%.
Research and development (R&D) costs were $33.8 million in the fourth quarter and $130.2 million for full year 2021. This represents an increase of 22% over the fourth quarter of 2020 and 21% compared to full year 2020 R&D costs as we continued to increase capabilities, opened our new R&D center in Glasgow, Scotland and further resourced our development teams for continued pipeline delivery.
Fourth quarter sales, marketing and administrative expenses were $37.4 million and full year 2021 sales, marketing and administrative expenses were $130.5 million. Reported R&D and sales, marketing and administrative expenses include $5.3 million of amortization and share based payment expenses in the fourth quarter of 2021 and $36.6 million in the full year 2021. In addition, we incurred listing expenses related to our merger and listing of $5.4 million in the fourth quarter and $36.2 million for the full year 2021. Excluding amortization, share based payment expenses and listing related charges, the non-IFRS adjusted operating loss for the fourth quarter was $11.4 million and for the full year 2021 was $72.6 million.
Net loss for the fourth quarter of 2021 was $37.2 million or $0.15 per fully diluted share. The net loss for 2021 was $100.8 million or $0.62 per fully diluted share. Our non-IFRS adjusted net losses for the fourth quarter 2021 and the full year 2021, excluding merger expenses and excluding amortization, share-based payment expenses, unrealized foreign exchange gains and other non-cash financing items were $20.0 million, or $0.08 per fully diluted share, and $111.6 million, or $0.68 per fully diluted share, respectively.
At December 31, 2021, we had $300.0 million in senior debt and $18 million in other term debt. Our cash balance at December 31, 2021 was $132.1 million.
Conference Call
LumiraDx’s senior management team will host a conference call today at 8:00 AM ET to discuss the company’s financial results and business updates. Call in details and a link to view the webcast may be found at https://investors.lumiradx.com/news-and-events/investor-calendar. A replay of the webcast will be available on the Investor’s section of the company’s website at investors.lumiradx.com shortly after the conclusion of the call. The webcast will be archived for 12 months.
About LumiraDx
LumiraDx (Nasdaq: LMDX) is a next-generation point of care diagnostics company that is transforming community-based healthcare. Founded in 2014, LumiraDx manufactures and commercializes an innovative diagnostic Platform that supports a broad menu of tests with lab comparable performance at the point of care. LumiraDx diagnostic testing solutions are being deployed by governments and leading healthcare institutions across laboratories, urgent care, physician offices, pharmacies, schools, and workplaces to screen, diagnose, and monitor wellness as well as disease. LumiraDx has, on the market and in development, 30+ tests covering infectious diseases, cardiovascular diseases, diabetes, and coagulation disorders, all on the LumiraDx Platform. In addition, LumiraDx has a comprehensive portfolio of fast, accurate, and cost-efficient COVID-19 testing solutions from the lab to point of need.LumiraDx is based in the UK with more than 1,600 employees worldwide.