There's No "P" in Coffee
By Arthur W. Young
At least, there shouldn’t be. This is about a case where there was.
I received a call from someone who wanted to know if it was possible to get a DNA profile from coffee. He explained that they suspected that someone urinated in the coffee pot at the office and the boss wanted to know whom. There are certain problems posed here. First of all, urine is an extremely thin bodily fluid, unlike blood, semen, and vaginal fluid, so the cells don’t stick to any surface that the urine comes in contact with. Instead, they tend to flow and settle. Second, the urine doesn’t contain cells unto itself; instead, they come from the lining of the body’s plumbing system. The number of cells in urine can vary from time of day, hydration state of the subject, male versus female, etcetera, but generally speaking, there are far fewer of them than found in other bodily fluids.
I’ve tested numerous urine samples for DNA. It seems that, as urine drug testing became more commonplace, so did challenging the results. When dealing with urine, one simply needs to let the cells settle on the bottom of the container and them collect a few for analysis. In this case, the comparative volumes between a pot of coffee and an average bladder were disparate, but not too far off. The same strategy of letting the coffee sit so that the cells could settle could work here. I could only hope that the coffee wasn’t destructive to the cells and/or DNA. I decided to give it a go and he said that he’d send the coffee in.
When the specimen arrived, it was about a gallon and a half, which was considerably more than I had expected. A quick call to the client revealed that it wasn’t so much a coffee pot as it was a coffee urn. The settling strategy was attempted but there was little settlement visible, even after being allowed to sit for two days in a refrigerator.
One of the hurdles that DNA analysts face when dealing with difficult cases is the fact that the sample has to fit into a microcentrifuge tube, which is a small plastic tube about the size of a small baby carrot. I needed to get all of the cells into that tube. Spinning the coffee in a centrifuge wasn’t practical, due to the volume. Filtering the coffee was a possibility, but a coffee filter (or even laboratory-grade filters) was still too big for the microcentrifuge tube. Filters can also get clogged by particulate matter, so some kind of force or pressure was needed.
I ultimately turned to the vacuum-swab, whose vacuum pressure, thick cotton filter, and replaceable filter units were features that had proven themselves to me time and time again. When attached to a sterilized vacuum flask, the filtered coffee could be saved for additional testing, like urea and creatinine (two chemicals that, if detected, would identify urine as being present) or drug metabolites.
After a few minutes of vacuum filtration, the filter was removed and analyzed for DNA. A DNA profile was generated: One source (as opposed to a mixture), male, and probably Caucasian. This information was passed back to the client and an investigation ensued at the office.
Within a couple of weeks, the client called and had reference buccal samples from three leading suspects at the office. All three were analyzed and one was found as a match.
The same vacuum-swab method was used in other cases where people either observed or suspected an employee at a restaurant spit in their drinks, such as iced tea, soda, lemonade, or water. Saliva, being far richer in cells than urine, is an easy source of DNA.
I received a call from someone who wanted to know if it was possible to get a DNA profile from coffee. He explained that they suspected that someone urinated in the coffee pot at the office and the boss wanted to know whom. There are certain problems posed here. First of all, urine is an extremely thin bodily fluid, unlike blood, semen, and vaginal fluid, so the cells don’t stick to any surface that the urine comes in contact with. Instead, they tend to flow and settle. Second, the urine doesn’t contain cells unto itself; instead, they come from the lining of the body’s plumbing system. The number of cells in urine can vary from time of day, hydration state of the subject, male versus female, etcetera, but generally speaking, there are far fewer of them than found in other bodily fluids.
I’ve tested numerous urine samples for DNA. It seems that, as urine drug testing became more commonplace, so did challenging the results. When dealing with urine, one simply needs to let the cells settle on the bottom of the container and them collect a few for analysis. In this case, the comparative volumes between a pot of coffee and an average bladder were disparate, but not too far off. The same strategy of letting the coffee sit so that the cells could settle could work here. I could only hope that the coffee wasn’t destructive to the cells and/or DNA. I decided to give it a go and he said that he’d send the coffee in.
When the specimen arrived, it was about a gallon and a half, which was considerably more than I had expected. A quick call to the client revealed that it wasn’t so much a coffee pot as it was a coffee urn. The settling strategy was attempted but there was little settlement visible, even after being allowed to sit for two days in a refrigerator.
One of the hurdles that DNA analysts face when dealing with difficult cases is the fact that the sample has to fit into a microcentrifuge tube, which is a small plastic tube about the size of a small baby carrot. I needed to get all of the cells into that tube. Spinning the coffee in a centrifuge wasn’t practical, due to the volume. Filtering the coffee was a possibility, but a coffee filter (or even laboratory-grade filters) was still too big for the microcentrifuge tube. Filters can also get clogged by particulate matter, so some kind of force or pressure was needed.
I ultimately turned to the vacuum-swab, whose vacuum pressure, thick cotton filter, and replaceable filter units were features that had proven themselves to me time and time again. When attached to a sterilized vacuum flask, the filtered coffee could be saved for additional testing, like urea and creatinine (two chemicals that, if detected, would identify urine as being present) or drug metabolites.
After a few minutes of vacuum filtration, the filter was removed and analyzed for DNA. A DNA profile was generated: One source (as opposed to a mixture), male, and probably Caucasian. This information was passed back to the client and an investigation ensued at the office.
Within a couple of weeks, the client called and had reference buccal samples from three leading suspects at the office. All three were analyzed and one was found as a match.
The same vacuum-swab method was used in other cases where people either observed or suspected an employee at a restaurant spit in their drinks, such as iced tea, soda, lemonade, or water. Saliva, being far richer in cells than urine, is an easy source of DNA.