Testosterone Levels. Should I be concerned?

51 year old male here. Last time I had my total testosterone checked in 2019, levels measured at 512 ng/dL which seemed about average. Recently had it retested last week and total was measured at 227.8 ng/dL which was kind of shocking that it took such a nosedive. Both tests were taken in the morning at 0730. I realize that testosterone typically decreases with age, but I didn't expect such a substantial drop.

I have made significant changed to my diet in that time. I was eating Keto in 2019 up until about a year ago, however, within the last year, I had to cut out trans and saturated fats because my LDL was in the danger zone. Currently on Zetia (non-statin) for Cholesterol. Still eat plenty of lean protein and take a multi-vitamin daily.

Physical activity and weight has varied over the past 6-7 years, but I still weight train and perform cardio at least 5 days a week. To be clear, I'm not a body builder by any stretch of the imagination. Lean Mass is around 65-70%. Body fat hovers around 25% if my Hume scale is to be believed.

Any idea would could account for such a drastic drop? Appreciate your comments and advice. Thanks.