No i haven't done a blood test, because I can't test everything which I think is depleted. I just supplement it and see what happens.
Without tests that may be very difficult. I started testing serum electrolytes and hair-mineral analysis regularly since 9 years ago. And even with regular hinds from those tests I'm still not there yet.
For example: showed below normal calcium in serum and hair the first 3 years. Only vitamin D3 (together with vitamin A and K2) brought that to normal (rather minimized supplemental calcium for avoiding soft-tissue classifications).
Had very painful muscle cramps mainly in neck, but everywhere else too, only since starting to supplement vitamin D3, which can ramp-up the utilization of magnesium greatly. Over time found I need at least 2 g of elemental magnesium supplemented to avoid these painful muscle cramps. Mg-deficiency didn't even show up in serum or hair lab tests, but in whole blood only (a substitution for RBC-Mg, not available from the labs where I live).
Sodium has been suboptimal in serum and very low in hair. The 3-4 gram of elemental sodium (note: elemental, as table salt that would be around 6 g/d!) I take at the moment hasn't resolved that yet (should get a new patch of tests soon..).
Potassium has been the easiest to correct (beside calcium with vitamin D3, which probably caused the Mg problems and further down-stream effects on all other electrolytes in the first place), by supplementing about 2 g per day.
Therefore, as my example shows, if one goes by what one is feeling from supplementing - in my case only felt the relieve from very high doses Mg - one can miss out on a lot happening at the same time.
Therefore would suggest to get at least once serum electrolytes tested from your GP as a minimum - to know how far off you are - and not to aggravate any other electrolytes further. And get a copy of the test-results, since most 'normal' lab ranges are taken from 95% of all persons tested, and which are usually very far from 'healthy' ranges. Examples from serum with my labs:
Sodium 136 - 145 mmol/mol (normal range); 142 -145 mmol/mol (~optimal range)
Calcium 2.2 - 2.55 mmol/mol (normal range); ~2,4 mmol/mol (~optimal range)
Potassium 3.5 - 5.1 mmol/mol (normal range); 4 - 5 mmol/mol (~optimal range)
Magnesium 0.66 - 1.07 mmol/mol (normal range); > 0,86 mmol/mol (~optimal range)
In the unlikely circumstance that your GP refuses these essential tests, where I live there are nearby labs where I can just walk in and each of them would cost my about €3,- only.