Hey.

There are various Masters courses that are available after you've completed the course of BMLT. Some of those are-

Post Graduate Diploma in Medical Laboratory Technology

Post Graduate Diploma in Laboratory Services in Science

Post Graduate Diploma in Biomedical Laboratory Technology (PGDBLT)

There are various areas in which you have an option to specialise in some of those are- 

Clinical chemistry

Clinical biochemistry

Microbiology

Biostatistics

Hematology

Molecular Biology and Applied genetics

Clinical Pathology

Coagulation

Biomedical Techniques

Cytotechnology

Ultrasonography

Phlebotomy

Urinalysis

Radiology and many more

Best of luck

Msc in Medical Laboratory Technology
Msc in medical imaging technology
Post graduate diploma in medicl laboratory technology
Post graduate diploma in Laboratory services in science
Post graduate diploma in Biomedical laboratory technology 

You can also go for MBA too .