Total solids (refractometer protein) in cats and dogs
Total solids is a quick estimate of plasma protein, read with a refractometer from the same small tube used for the hematocrit. It takes a minute, so it is often part of an in-clinic blood count. It is a screen rather than an exact number: an accurate total protein comes from the chemistry analyzer.
What it shows
After the hematocrit tube is spun, the clear plasma above the cells is placed on a refractometer, which measures how strongly it bends light (the refractive index). Proteins give most of that effect, but other dissolved substances add to it — hence the name “total solids”. Plasma also contains fibrinogen, which serum lacks, so total solids usually reads higher than total protein from the chemistry analyzer, especially in dogs and cats. Both manual and digital refractometers read higher than the analyzer.
At the same moment the colour of the plasma is noted: yellow in a dog or cat means jaundice, red means free hemoglobin (usually red cells broken in the tube, sometimes in the body), white and cloudy means fat in the blood (lipemia).
Higher than reference — what it may be a sign of
- More protein: very high values, above 9.0 g/dL, are usually due to more globulins, including fibrinogen. Together with red cells stacked like coins (rouleaux) this suggests inflammation or a tumour of B cells or plasma cells.
- Lipemia: fat particles falsely raise the reading, so the result is usually cancelled in a lipemic sample.
- Other dissolved substances: glucose above 300 mg/dL is the worst offender; sodium, chloride, urea and creatinine also add to the reading, as do colloid fluids given through a drip.
- Hemolysis: free hemoglobin is counted as protein, and on a manual refractometer it also blurs the reading line.
Bilirubin, on the other hand, does not affect the result.
Lower than reference
- Protein loss: blood loss, protein loss through a diseased gut or the kidneys.
- Protein breakdown or too little intake.
- Immune deficiency, such as a newborn that did not receive antibodies from colostrum (failure of passive transfer).
- Young growing animals naturally have lower values.
A low total solids in an anaemic animal points the vet towards blood loss.
Look at together with
- Hematocrit — read from the same tube. In anaemia, plasma protein is often low with blood loss, but normal or high with breakdown of red cells or reduced production.
- Total protein from the chemistry panel — the accurate measurement; the two numbers are not interchangeable.
- Albumin and globulin — show which part of the protein has changed.
- Fibrinogen — part of plasma protein, counted in total solids but absent from serum total protein.
Units and conversion
North American forms usually give g/dL, European and Russian forms g/L. One g/dL equals 10 g/L, so 6.5 g/dL is 65 g/L. In the app each row keeps the unit printed on the form; the chart converts to one unit. Even in the same unit, a refractometer value and an analyzer value are different measurements, so a trend is followed with one method.
Reference range
The reference range is on your lab’s form. Plasma and refractometer values run higher than chemistry total protein, so the two numbers are not compared directly. Small differences between repeated readings are part of the method: in one laboratory’s own data, repeat readings of the same sample differed by 0–0.4 g/dL. A lipemic or severely hemolysed sample may give no result at all.
Cats and dogs
In cats, as in dogs, yellow plasma in the hematocrit tube means jaundice — unlike horses and cattle, where it is normal. Refractometer values run above analyzer values more in dogs and cats than in large animals. In a cat with very high blood glucose, such as in diabetes, the reading can be falsely raised.
White, cloudy plasma is normal in dogs after a meal; outside that it can come with acute pancreatitis, Cushing’s syndrome (hyperadrenocorticism), nephrotic syndrome or an underactive thyroid, and it occurs in some breeds such as Schnauzers. Because lipemia falsely raises total solids, a fasting sample gives a more reliable reading. Puppies have naturally lower values.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.