The Autopsy Posts: Acid Phosphatase as Evidence of Recent Sexual Activity or Decomposition

This is my third post about autopsies following my first and second posts. Once again I will be looking at the autopsy report for Hae Min Lee. In relevant part, it states:

In other words, when a victim’s body has certain units per liter of acid phosphatase, it can be indicative of recent sexual activity because the enzyme is present in large amounts in seminal fluid. Therefore, one might speculate that Lee had engaged in recent sexual activity before her death. That said, the anal, oral, and vaginal swabs of her body were negative for spermatozoa. This takes us to the alternate explanation for the presence of elevated levels of acid phosphatase and why we can rule the enzyme out as evidence of recent sexual activity.

Let’s start with the testimony of Stephen S. Radentz, M.D., in State v. Perry, 2010 WL 6768345, a case also heard in the Circuit Court for Baltimore City:

Q. Please tell the jury what was done and why.

A. This is part of a sexual assault kit in which we swab various areas looking for evidence of — the presence of sperm or acid phosphatase. In this case we swabbed the vaginal area, the oral area and the anal area. And acid phosphatase is an enzyme which is produced in very high levels in the prostate in seminal vesicles. So in ejaculate it is an extremely high level of acid phosphatase. Now this enzyme is also present in very low levels in other areas where secretions are present such as the mouth and the anus and the vagina.

But the level — you can tell by how high the level is to whether or not the likelihood of seminal fluid being present is there. And the cut off is in the area of 100 to 400 units per liter. 100 is equivocal, you know, the possibility. If it’s much above 100 then there’s a very good likelihood seminal fluid is present. We also at the same time, we collect these swabs to check for acid phosphatase we also make slides of the swabs and examine those for the presence of sperm.

And in Ms. Jordan’s case the vaginal swab had an acid phosphatase level of 100 which is high, but it’s sort of in the equivocal range. It may indicate the presence of semen. It may not. The oral and anal swabs were very low. They were 16 and 29 units per liter respectively and would reflect the normal background level of acid phosphatase. And would not be suspicious. Now the slides that we prepared from these swabs were examined microscopically for the evidence of — the presence of sperm. The oral and rectal slides, there was no sperm identified. However, the vaginal swab and slide showed the presence of rare sperm present.

Now, compare this testimony with the findings in the autopsy report for Hae Min Lee:

VAGINAL SWAB: Acid Phosphatase 136 U/L [units per liter]

ORAL SWAB: Acid Phosphatase 107 U/L

Given this, you might initially suspect recent sexual activity. But keep in mind that Lee’s body was found almost a month after her death. Then, take a look at these two sources of information:

Rapid Detection of Sperm: Comparison of Two Methods: 

On the other hand, acid phosphatase detection and measurement techniques are hampered by the limited duration of enzyme activity. In our study, the longest timespan after which detection was possible was 106 h[ours] between intercourse and sampling.

Time Since Intercourse: Studies and Estimates:

Conclusion: AP test is not precise indicator of TSI [Time Since Intercourse]. Best to determine interval limit beyond which value is unlikely. Example: > 256 U unlikely after 12 hours; values 64-128 U unlikely after 24 hours.

In other words, using U/L of acid phosphatase is only useful to determine whether there was recent sexual intercourse if testing is done soon after intercourse, possibly as soon as a day after intercourse. This is because there are unlikely to be elevated acid phosphatase levels based on seminal fluid long after intercourse.

So, why did Lee have elevated levels of acid phosphatase? Well, according to this article,

Pathologists cautioned that the acid phosphatase test is not reliable because the enzyme it detects can also be found in other bodily fluids, including vaginal fluids and fluids produced by a decomposing body.

After reading this article, I got information from one of the pathologists who gave me information regarding lividity. He confirmed that Lee’s U/L levels of acid phosphatase were entirely consistent with decomposition and could not come from seminal fluid, which, in any event, wasn’t found during swabbing.

-CM