SAMPLING METHODS USED IN ROUTINE SEROLOGY

Methods of obtaining samples for serological examination must be practical, easy to teach to farm staff, and produce serum of appropriate quality and quantity for the intended test(s).

1. Obtaining a blood sample.

Having determined the number and type of birds to sample (see statistical basis of sampling above) the first task is to obtain a sample of the required volume. The options are :

1a. Cardiac puncture using a syringe and needle. This method has the advantage of quickly providing a clean and uncontaminated sample of ample volume. The disadvantages are the need for having sterile 5 ml syringes and 18g x 1 inch needles available on farm, the greater difficulty in training staff to take such samples, and, for birds weighing over 500 grams, 2 people are required, one to take the sample and the other to hold the bird in dorsal recumbency. It is possible to approach cardiac puncture via the thoracic inlet, though, in the authors experience, this is more difficult to teach and results in a higher fatality rate than a antero-medial approach. The method for the antero-medial approach in chickens may be described as follows:

I. With the bird held in dorsal recumbency, palpate the apex of the bony triangle formed by the sternum and the metasternum, preferably on the right hand side.

II. Insert the needle at the indicated point, directing it at 45 degrees to both vertical and horizontal planes, or in the direction of the base of the contra-lateral wing (shoulder joint). If bone is struck it may be necessary to re-direct the tip of the needle to enter the thorax.

III. On entering the thorax, apply a slight vacuum while gently progressing the tip of the needle in the indicated direction. Stop this progression as soon as a satisfactory flow comes into the syringe.

IV. If the flow of blood suddenly stops the likely cause is that the cardiac endothelium has been sucked into the lumen of the needle. In this case simply release the vacuum temporarily and rotate the barrel of the syringe slightly before re-applying vacuum, maintaining the tip of the needle in roughly the same place.

1b. Puncture of a peripheral vein using a syringe and needle. Some people find it easier to learn to collect a blood sample from a superficial vein because the source of the blood can be visualized. In chickens and turkeys it is customary to use the brachial vein near the ventral surface of the elbow joint. In ducks a superficial tarsal vein above the hock is used. The method may be described as follows:

I. Hold the bird by extending both wings dorsally, gripping them firmly together with the left hand. Pluck feathers over the puncture site. Swabbing the site with a small amount of 70% alcohol may help visualize the vein.

II. Insert the needle slightly anterior to the vein and in the direction of the tip of the wing (i.e. against the flow of blood). Re-direct the needle to puncture the vein.

III. Withdraw the sample by applying gentle vacuum.

1c.Stabbing a peripheral vein Most farm staff can quickly learn to take a reasonable sample using this technique. The sampling site is prepared as in 1b. above. Instead of puncturing the vein with a hypodermic needle it is simply stabbed with the tip of a scalpel blade (usually No. 11), or a straight triangular surgical needle. The blood may be collected as a droplet in the hollow on the ventral surface of the wing and allowed to run into the receptacle being used.