Denver International Airport is 5431 feet above sea level. When the temperature is at standard conditions (about 45 degrees for that altitude), then density altitude is equal to pressure altitude. However, when the temperature is hotter than standard, the density altitude can be much higher.

Last Sunday morning, I took off from Meadowlake Airport (6840 feet above sea level). It was a pretty warm morning, so the density altitude was 9700 feet. My plane doesn't exactly have an angelic rate of climb on a good day. Last Sunday, it was only climbing a few hundred feet per minute.

Like all aircraft, airliners are flight tested for a range of parameters including density altitude. When density altitude exceeds the tested values, the plane can't be legally flown. It got up to 105 degrees F in Denver last Wednesday. That almost certainly meant the density altitude was above 10,000 feet.