From “What to order?” to “What did I order?”

This week, we are back with two memory tricks for lab tests. The first will help you remember the broad categories of tests that you may want to order when you have collected a sample (e.g. pleural fluid, synovial fluid, cerebrospinal fluid). The second will help you keep your PT and PTTs straight in your mind.

1) The 4 Cs for fluid analysis (note: all may not apply):

Chemistry (e.g. pH, LDH, glucose, protein)

Cell count and differential



2) PT is a measurement of the extrinsic pathway and PTT is a measurement of the intrinsic pathway. You can remember this using the following memory aid:

PTT has the extra T “in” it and therefore is the intrinsic pathway. PT has the extra “T” excluded and therefore reflects the extrinsic pathway.


Hopefully you will find this to be helpful on the wards. Thanks for reading!

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