Turning to our mental health business, we delivered 10,921 IDgenetix test reports in 2023 compared to 3,249 test reports in 2022, which is more than 200% growth. We believe a significant driver of growth is our differentiated tests for the treatment of mental health conditions, including identifying drug-drug, drug-gene, and lifestyle factors to improve medication response or remission rates in a large, underpenetrated mental health market. In fact, real-world evidence confirms a consistent impact of IDgenetix on medication response and remission rates in patients with major depressive disorder, or MDD. Specifically, the study found that real-world patient outcomes are strongly aligned to the result of a previously-published randomized control trial, which show that patients whose medication management was guided by IDgenetix were 2.65 times more likely to achieve remission of depressive symptoms compared to patients whose medications was not guided by our tests.
Moving on to our inflammatory disease pipeline initiative to develop a genomic test, or series of tests, aimed at predicting response systemic therapy in patients with moderate-to-severe atopic dermatitis, psoriasis, and related conditions. Last quarter, we shared some early yet promising discovery data. The data demonstrated that in patients with moderate-to-severe atopic dermatitis, we’re able to show that using our noninvasive method of tissue sampling, coupled with gene expression profiling, can separate out responders to nonresponders. Furthermore, our inflammatory skin disease pipeline tests could help distinguish a atopic dermatitis, psoriasis, and mycosis fungoides skin lesions to help ensure proper therapy selection based upon an individual patient’s molecular profile.
We expect to provide you with additional development updates in the second half of 2024 with a test targeted for launch by the end of 2025, assuming a positive outcome of our discovery, development, and validation efforts. I will now turn the call over to Frank, who will provide details relating to our financial results and outlook.
Frank Stokes: Thank you, Derek, and good afternoon, everyone. Reiterating Derek’s sentiment, we’re excited with the strong year we had in 2023 and the momentum we are carrying forward. In the fourth quarter of 2023 we delivered total revenue of $66.1 million, a 72% increase over the fourth quarter of 2022, and we delivered $219.8 million for the full year 2023, a 60% increase over 2022. The increase was driven by higher ASPs and test volume growth. Adjusted revenue, which excludes the effects of revenue adjustments in the current period related to tests delivered in prior periods, was $70.2 million for the quarter, and $224.3 million for the full year 2023. For 2024, we anticipate generating total revenue of $235 million to $240 million, driven by further consistent execution on our growth plans.
Our gross margin in the fourth quarter was 77.8% compared to 69.4% in the fourth quarter of 2022, and our gross margin for the full year was 75.4% compared to 70.6% in 2022. Our adjusted gross margin, which excludes the effects of intangible asset amortization related to our acquisitions, and excludes the effects of revenue adjustments in the current period associated with test reports delivered in prior periods was 82.3% for the quarter, and 79.9% for the year, compared to 74.6% and 77% for the same periods in 2022. Turning to expenses, our total operating expenses, including cost of sales for the quarter ended December 31, 2023, were $71.8 million compared to $61.2 million for the prior year, and were $287.8 million for the full year compared to $209.9 million for 2022.
Sales and marketing expense increased by $27.1 million or 31.2% for the year ended December 31, 2023, compared to the year ended December 31, 2022, primarily attributable to higher personnel costs. General and administrative expenses increased by $10.1 million or 17.9% for the year ended December 31, 2023 compared to the year ended December 31, 2022, primarily attributable to higher personnel costs and higher information technology and software related costs. R&D expense increased by $1.7 million in the fourth quarter, and by $8.7 million for the full year 2023 compared to 2022, primarily consisting of higher personnel costs and higher clinical studies expense, partially offset by lower expense from advisory boards and consulting services. Total non-cash stock-based compensation expense, which is allocated among cost of sales, R&D expense, and SG&A expense, totaled $51.2 million for the year ended December 31, 2023, compared to $36.3 million for the year ended December 31, 2022.
We expect material increases in stock-based compensation expense in future periods attributable to both existing awards outstanding and anticipated additional grants to our current and future employees. We expect to complete an annual grant of equity awards to our employees in March of 2024. Interest income was $10.6 million for the full year 2023 compared to $4 million in 2022, primarily a result of higher interest rates and/or purchases of marketable investment securities beginning in the third quarter of 2022. Our net loss for the fourth quarter of 2023 was $2.6 million, compared to a net loss of $20.6 million for the fourth quarter of 2022, and our net loss for the full year 2023 was $57.5 million compared to a net loss of $67.1 million for 2022.
Diluted loss per share for the fourth quarter was $0.10 compared to diluted loss per share of $0.17 in the fourth quarter of 2022. Diluted loss per share for the full year 2023 was $2.14 compared to diluted loss per share of $2.58 for 2022. Adjusted EBITDA for Q4 was $9.4 million compared to negative $10.4 million for the comparable period in 2022, an improvement of $19.8 million. For the full year 2023 adjusted EBITDA was negative $4.4 million compared to negative $42.6 million in 2022, an improvement of $38.2 million. Net cash provided by operating activities was $18.6 million for the fourth quarter, and net cash used in operating activities was $5.6 million for the year ended December 31st, 2023. We expect the first quarter of 2024 to be a net operating cash use quarter due to annual cash bonus payments and certain healthcare benefit payments that are not expected to recur during the remaining three quarters of 2024.
Net cash used in investing activities was $15.2 million for the 12 months ended December 31, 2023, and consisted primarily of purchases of marketable investment securities of $189.1 million and purchases of property and equipment of $13.6 million, partially offset by the maturity of marketable investable securities of $186.5 million. We increased our cash position by more than $13 million in the fourth quarter of 2023 compared to the third quarter of 2023, ending the year with cash, cash equivalents and marketable securities of $243.1 million. In the current high interest rate environment, we believe our strong financial position allows us to continue to invest in our business, execute on our strategic growth plans, and maintain our competitive lead.
