diff --git a/NEWS.md b/NEWS.md
index 43ca82d0..d39d115a 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -74,6 +74,7 @@ the dosing including dose amount and route.
   for grouped joins, preserving left-table row order. Missing group validation
   ensures no rows are silently dropped.
 
+* `PKNCAresults()` now includes `start` and `end` in `group_vars`
 
 ## Breaking changes
 
diff --git a/R/class-PKNCAresults.R b/R/class-PKNCAresults.R
index 41dc16b1..acfcd4ec 100644
--- a/R/class-PKNCAresults.R
+++ b/R/class-PKNCAresults.R
@@ -398,5 +398,5 @@ getGroups.PKNCAresults <- function(object,
 #'   from the PKNCAconc object within
 #' @exportS3Method dplyr::group_vars
 group_vars.PKNCAresults <- function(x) {
-  group_vars.PKNCAconc(as_PKNCAconc(x))
+  c("start","end",group_vars.PKNCAconc(as_PKNCAconc(x))) 
 }
diff --git a/tests/testthat/test-class-PKNCAresults.R b/tests/testthat/test-class-PKNCAresults.R
index 87e19f66..effac1d8 100644
--- a/tests/testthat/test-class-PKNCAresults.R
+++ b/tests/testthat/test-class-PKNCAresults.R
@@ -421,14 +421,14 @@ test_that("group_vars.PKNCAresult", {
   o_data_group <- PKNCAdata(o_conc_group, intervals = data.frame(start = 0, end = 1, cmax = TRUE))
   suppressMessages(o_nca_group <- pk.nca(o_data_group))
 
-  expect_equal(dplyr::group_vars(o_nca_group), "Subject")
+  expect_equal(dplyr::group_vars(o_nca_group), c("start", "end", "Subject"))
 
   # Check that it works without groupings as expected [empty]
   o_conc_nongroup <- PKNCAconc(as.data.frame(datasets::Theoph)[datasets::Theoph$Subject == 1,], conc~Time)
   o_data_nogroup <- PKNCAdata(o_conc_nongroup, intervals = data.frame(start = 0, end = 1, cmax = TRUE))
   suppressMessages(o_nca_nogroup <- pk.nca(o_data_nogroup))
 
-  expect_equal(dplyr::group_vars(o_nca_nogroup), character(0))
+  expect_equal(dplyr::group_vars(o_nca_nogroup), c("start","end"))
 })
 
 test_that("as.data.frame.PKNCAresults can filter for only requested parameters", {