at our laboratory, the relevant information about the test is entered into our computer system, and the test sample is routed into the appropriate workflow. This number is a subset of the number of tests that we process, which includes tests distributed through our Constellation licensees. The number of tests that we process is a key metric as it tracks overall volume growth, particularly as our laboratory partners may transition from sending samples to our laboratory to our cloud-based distribution model, as a result of which our tests accessioned would decrease but our tests processed would remain unchanged.
During the six months ended June 30, 2023, we processed approximately 1,243,400 tests, comprised of approximately 1,206,700 tests accessioned in our laboratory, compared to approximately 989,200 tests processed, comprised of approximately 957,200 tests accessioned in our laboratory, during the six months ended June 30, 2022. This increase in volume primarily represents continued commercial growth of Signatera, Panorama and HCS, both as tests performed in our laboratory as well as through our Constellation software platform.
The percent of our revenues attributable to our U.S. direct sales force for the six months ended June 30, 2023 was 90%, a slight increase compared to 89% for the six months ended June 30, 2022. The percent of our revenues attributable to U.S. laboratory distribution partners for the six months ended June 30, 2023 was 7%, flat compared to the same period in the prior year. Our ability to increase our revenues and gross profit will depend on our ability to further penetrate the U.S. market with our direct sales force. The percent of our revenues attributable to international laboratory distribution partners and other international sales for the six months ended June 30, 2023 was 3%, flat compared to the six months ended June 30, 2022.
For the six months ended June 30, 2023, total revenues were $503.2 million, compared to $392.3 million in the six months ended June 30, 2022. Product revenues accounted for $496.1 million, 99% of total revenues for the six months ended June 30, 2023 compared to $384.6 million representing 98% of total revenues for the six months ended June 30, 2022. For the six months ended June 30, 2023 and 2022, no customers exceeded 10% of the total revenues on an individual basis. Revenues from customers outside the United States were $16.6 million, representing approximately 3% of total revenues for the six months ended June 30, 2023. For the six months ended June 30, 2022, revenues from customers outside the United States were $13.2 million, representing approximately 3% total revenues. Most of our revenues have been denominated in U.S. dollars, though we generate some revenue in foreign currency, primarily denominated in Euros and Singapore Dollars.
Our net loss for the six months ended June 30, 2023 and 2022 was $247.7 million and $283.7 million, respectively. This included non-cash stock compensation expense of $85.2 million and $76.1 million for the six months ended June 30, 2023 and 2022, respectively. As of June 30, 2023, we had an accumulated deficit of $2.2 billion.
Components of the Results of Operations
Revenues
We generate revenues from the sale of our tests, primarily from the sale of our Signatera, Panorama and HCS tests. Our two primary distribution channels are our direct sales force and our laboratory partners. In cases where we promote our tests through our direct sales force, we generally bill directly to a patient, clinic or insurance carrier, or a combination of the insurance carrier and patient, for the fees.
Sales of our clinical tests are recorded as product revenues. Revenues recognized from tests processed through our Constellation model, from the Qiagen LC (“Qiagen”), BGI Genomics Co. Ltd., and Foundation Medicine, Inc. agreements (collectively the “Strategic Partnership Agreements”) are reported in licensing and other revenues.
In cases where we sell our tests through our laboratory partners, the majority of our laboratory partners bill the patient, clinic or insurance carrier for the performance of our tests, and we are entitled to either a fixed price per test or a percentage of their collections.
Our ability to increase our revenues will depend on our ability to further penetrate the domestic and international markets and, in particular, generate sales through our direct sales force, develop and commercialize additional tests, obtain