The average return credit is calculated by dividing the actual shock credits issued by the actual number of trodes returned. A variance in the assumed return rate compared to the actual rate would impact the estimate and potentially understate net sales (overestimated rate) or overstate net sales (underestimated rate) in any given year and create a corresponding misstatement of the liability due to customers.
On March 31, 2022, the estimated value of our Therapeutics customer contract liability was $303. If the expected return rate was increased by 2%, the effect on current year reduction in sales and increase in customer liability would have been $21.
Results of Consolidated Operations
Revenue
Revenue for the three months ended March 31, 2022, was $3,751 compared to $14 for the three months ended March 31, 2021, an increase of $3,737. Revenue in the current period primarily resulted from the inclusion of our PulseVet platform, which had revenues of $3,694, consisting of instruments, trodes and warranty services sold worldwide. Revenues from sales of cartridges from our TRUFORMA® platform were $57 for the three months ended March 31, 2022, compared to $14 for the three months ended March 31, 2021, an increase of $43, or 307%. We launched our TRUFORMA® platform in March 2021. In general, we expect revenue to increase in subsequent periods as we increase our sales and marketing of the PulseVet platform which we acquired on October 1, 2021, and as additional assays are added to our TRUFORMA® platform.
Cost of Revenue
Cost of revenue for the three months ended March 31, 2022, was $990 compared to $6 for the three months ended March 31, 2021, an increase of $984. Cost of revenue primarily resulted from costs associated with sales of our PulseVet platform which totaled $944, as well as $46 from costs associated with sales of our TRUFORMA® platform. We anticipate that costs of revenue will increase in 2022 as we increase revenue as described above.
Gross Profit
Gross profit for the three months ended March 31, 2022, was $2,761 compared to $8 for the three months ended March 31, 2021, an increase of $2,753. Gross profit margin for the quarter ended March 31, 2022, was approximately 74%, compared to 60% for the quarter ended March 31, 2021, an increase of 14%. The increase in gross profit resulted primarily from the inclusion of our PulseVet platform in the first quarter of 2022. In general, we believe gross margins will remain relatively unchanged due to a variety of factors, including the ability to effectively stimulate demand for certain of our products; potential increases in the cost of components and outside manufacturing services; our ability to manage warranty costs effectively; shifts in the mix of products and services, or in the geographic, currency or channel mix; and fluctuations in exchange rates.
Research and Development
Research and development expense for the three months ended March 31, 2022 was $351 compared to $413 for the three months ended March 31, 2021, a decrease of $62, or 15%. The decrease was the result of a reduction in research and development activity associated with TRUFORMA® as we completed development of the instrument and three of the first five assays and began commercialization in March of 2021.
Selling, General and Administrative
Selling, general and administrative expense for the three months ended March 31, 2022 was $6,722, compared to $3,468 for the three months ended March 31, 2021, an increase of $3,254, or 91%. The increase primarily was due to an increase in share-based compensation expense which was $2,041 for the three months ended March 31, 2022 compared to $1,283 for the comparable period in 2021 as a result of stock option grants made during the first quarter of 2022, as well as an increase in compensation expense of $1,373 due to additions to our sales force and management team and from the