Body fluid samples
Blood and other fluids are necessary for analysis in toxicological, biochemical, microbiological and serological investigation. It is not advisable to use residual blood present in cavities for analysis and considerable care must be applied in sampling. Earlier, heart blood was considered ideal for analysis. However, the modern schools suggest collection of peripheral blood from femoral or subclavian veins, ideally before autopsy is started.
Aspirating 20ml of blood by puncturing femoral veins by a needle or syringe before dissection is the method of choice, especially if only external examination is to be performed. Subclavian or external iliac veins can be used in case the body has already been eviscerated.
A cut across the iliac veins at the brim of the pelvis can provide a significant amount of blood, provided this is done before evisceration. Similarly, the internal jugular vein also provides a copious amount of blood. After the skin has been dissected off the neck, the internal jugular vein is exposed by dividing the sternomastoid muscle. When cut, a copious flow of blood is usually obtained, that can be collected directly into a container.
Urine is collected using a catheter before autopsy or using supra-pubic puncture with a syringe and long needle during autopsy. It is obtained after the abdomen has been opened, but before the organs are removed. Extra care should be taken not to contaminate the urine with blood.
Vitreous humor can be aspirated with a hypodermic needle attached to a 5 ml syringe. It is inserted into the outer canthus of the eyeball after pulling the eyelid aside so that when released it covers the puncture mark.
The needle must be directed towards the center of the globe to avoid aspirating material and both eyes should be used, as their chemical composition often varies. Collapsed eyeball following removal of vitreous is re-inflated with water, for cosmetic purposes.
Cerebrospinal fluid may be obtained by passing a needle into the theca between the lumbar spines. An alternate to this is by performing a cisternal puncture through the atlanto-occipital membrane. Any attempt to obtain clear cerebrospinal fluid from the interior of the skull after removal of the brain is not recommended, owing to false positive results.