How should urine and blood samples be stored before they are sent to the laboratory?
Generally urine and blood samples can be stored in the refrigerator at 4°C. For the measurement of cocaine in the blood fluorid should be added to stabilize the sample.
How long are the samples stored at the laboratory?
The storage time at the Laboratory Krone is:
Clinical urine samples: 1 week
Urine samples for MPA: 6 months
Hair samples: 6 months
Forensic urine samples: 2 years
Forensic blood samples: 2 years
What is the chain of custody?
The chain of custody designates the complete documentation of all pre-analytical and analytical steps in the analysis of a sample. This includes all procedures starting from the identification of the person to be tested with his or her identity card, the sample collection, the transport of the sample to the laboratory, the technical analysis of the sample and finally the issuing of a report or a written expert testimony.
What is the meaning of cut-off value?
The cut-off value is the concentration of a substance above which a result is considered "positive". In contrast, if the concentration e.g. of a drug of abuse in urine is below the pre-defined cut-off the result is considered "negative".
The cut-off value is generally higher than the limit of quantification (LOQ). For example, if the cut-off value of cannabis in urine is 10 µg/L, it means that all values below 10 µg/L are negative. The analytical limit of quantification (LOQ) with immunoassay or a chromatographic method (GC-MS) is much lower. So if a cannabis concentration of 5 µg/L is measured, the result is regarded as negative. The reason is the need to avoid that a low cannabis concentration as a result of passive smoking causes a positive cannabis test result.
How much time is needed for a hair analysis?
The result of negative hair test for seven drugs is available within 5 days. If a positive screening test has to be confirmed with a chromatographic method (GC-MS or LC-MS/MS) another 5 working days may be necessary.
Can the result of hair analysis be adulterated by a previous cosmetic treatment of the hair?
Coloring, discoloring and bleaching can reduce the concentration of drugs of abuse and ethylglucuronide in the hair.
Which laboratory tests are available for the detection of alcohol abuse?
Besides the determination of non-specific marker such as yGT, AST, ALT and the MCV (mean corpuscular volume of the erythrocytes) the following tests can done: CDT (Carbohydrate-deficient transferrin) which is a good marker of increased alcohol consumption, particularly if the analysis is performed with HPLC (high pressure liquid chromatography). The detection of the asialotransferrin fraction is regular alcohol consumption. A disadvantage of the method is that the variability of the CDT concentration can be caused by a genetic polymorphism. Results of the low-priced immunological tests are less certain and should be confirmed with HPLC.
Ethylglucuronide in urine is a very reliable marker of alcohol consumption. This can be explained by the fact that ethylglucuronid is a direct metabolite of alcohol and the analysis with GC-MS is very specific.
Ethylglucuronide in hair is a long-term indicator of alcohol consumption. The detection with GC-MS/MS or LC-MS/MS is very reliable and high concentrations a proof of alcohol intake. A further advantage is that based on the concentration found it is possible to differentiate between moderate and excessive alcohol consumption. A negative result is evidence for alcohol abstinence or very low alcohol intake.