Calibrate that refractometer
Have you ever attempted to solve a problem that doesn't exist?
I had this experience this week. My client had a "problem" with low immunity values among calves. They had an unexpected drop in blood serum total protein readings.
They are quite consistent in drawing blood at approximately the same time each day. Samples always are allowed to sit undisturbed for about 24 hours before the same person uses the farm's clinical refractometer to assess BSTP values.
As we started to work on the "problem" I routinely asked about their protocol for calibrating the clinical refractometer. She could not recall when that was last done. We found some distilled water. Oooooops!
Somehow the refractometer was reading between 0.3 and 0.4 low. We tinkered with the adjustment screw and repeated the distilled water readings until the right-hand scale read "0."
Then we repeated the BSTP reading for the blood samples we had on hand.
Presto! The "problem" of low blood serum total protein values disappeared.
When I was doing on-farm BSTP readings I calibrated every Monday - the idea is to have some regular schedule - maybe even write it on a calendar?
Just as an aside, in the absence of distilled water I have used sterile water (usually have some on hand) to calibrate my hand held refractometer. I get the same reading as distilled water so in a pinch the sterile water probably is better than not calibrating at all.