The first reason may be related to your lab set-up, have you integrated with your lab?
In order to make sure you have set up your lab correctly click here and scroll down to "Lab accounts".
Second, are your lab products marked as "Labs?"
If you click "Products" at the top of your page you will see a list of all the products you've added to your system:
If you go through this list, make sure that the "Name" (e.g. Cervical Smear + HPV Testing) has "Product Type" as "Lab":
If this isn't marked as "Lab" as above then click the name of the product and you will be led to the below:
Click "Edit" and you'll be taken to the page below. Click the field in "Type" and a drop down menu will appear, make sure you select "Lab", click "Save" once complete:
To use this lab product you have just created you need to insert it into the "Product" section when writing a consultation, the lab will not be able to be ordered if the product section is not being utilised:
Finally, in "Settings" and then "Users" have you selected "Yes" to the question: "Is this user a practitioner?" This needs to be selected "Yes".