The Results are In - 2nd post

There are LOTS of things that can be measured using serum or plasma. What I want to focus on here are the typical things we look for on a "general chemistry" or "blood chem" or "chem 6, 12, 27" or whatever.

Serum or plasma is the golden to clear liquid that is left on top after you spin all of the cells down and out of the blood. (Serum has the clotting factors and such spun out, Plasma is blood with everything BUT the cells)

Most of the things we are testing for are either waste products, electrolytes, or enzymes. The enzymes we measure are leaked out of tissues (like liver cells or pancreas) and there is always a little bit of "normal" leakage going on.

Let's break them down into groups:

Kidney

• BUN or Blood Urea Nitrogen. BUN is made by the liver from the ammonia produced when the body burns proteins. BUN is then eliminated from the body by and large from the kidneys. It is a very labile compound and can rise and fall quickly. Usually an increased BUN is associated with kidney dysfunction
• Cr or Creatinine. Cr is a waste product from muscle (mostly). It is also excreted by the kidneys. Cr is much less labile than BUN and tends to rise slowly. It is also a good indicator of renal disease. I think of Cr as the "chronic" indicator and BUN as the "acute" indicator.

Electrolytes

• All of the electrolytes are tightly regulated by the body. It's really amazing! The gut will dump electrolytes like chloride when needed. The kidneys dump sodium and potassium if needed. There are complex mechanisms by which the kidneys trade sodium, chloride, potassium, and bicarbonate and all of this is influenced by certain hormones like aldosterone and cortisol. The pH of the blood is regulated by a whole host of processes. Electrolyte regulation and pH regulation rely on each other. Additionally, the lungs (respiratory rate and function) build up or blow-off carbon dioxide. The carbon dioxide turns into bicarbonate in the blood and the pH raises and lowers accordingly. It is a fascinating process and I've just summed up entire textbooks in this paragraph.
• No one electrolyte can be looked at by itself. When evaluating these, we have to look at all of them together and ratios between them all.
• Sodium is one of the three "main" electrolytes we measure. It is very labile and can change quickly. Sodium tends to increase with dehydration. It is somewhat influenced by diet, but the body dumps extra sodium in the urine if extra sodium is in the food.
• Chloride is an electrolyte that doesn't get much respect. Probably because it tends to follow sodium around. Chloride can change fairly dramatically in cases of vomiting and diarrhea, but I have trouble getting too excited about chloride.
• Potassium is probably the one electrolyte that people pay the most attention to. It can reach dangerously high or low levels in many different disease processes and it is the one electrolyte that we are usually trying hardest to address. When the blood is more acid (like in a sick diabetic) the potassium is dangerously low. Vomiting also produces low potassium. Potassium is high when we can't urinate (as in cases of blocked tom cats). High potassium causes the heart to slow way down and stop. There is 35 times more potassium IN your cells than OUT of your cells. When total body potassium is low, it can take quite a while to get it back up.
• Magnesium - not measured often enough. Can be way off with GI disease. Not usually supplemented much, although when it is low, these patients feel MUCH better when magnesium is corrected.
• Phosphorous/Calcium - these two are like yin and yang to each other. Phosphorous will increase dramatically in cases of kidney failure. Calcium can go up and down with albumin (since albumin carries this electrolyte). Low blood calcium that happens immediately after giving birth is called eclampsia or milk fever.

Liver

• Most liver enzymes we check are enzymes made by the liver and contained within the liver cells. The idea is that damage to the liver or stress to the liver cells will cause them to "leak" more enzyme causing blood levels to increase.
• ALT (alanine amino transferase) - This one is the most specific to liver "damage" or "disease." ALT goes up when the liver cells are killed or squished (hit by car animals have high ALT because the liver was squished).
• ALKP (alk phos, alkaline phosphatase) - This enzyme is not exclusive to the liver. It's also made in bone and white blood cells, so increases in this level must be looked at in perspective. It is much more important in the cat. Increases in the cat are almost always associated with liver upset.
• Albumin - the blood protein found in the largest quantity in the blood. It is made by the liver and chronic liver dysfunction can cause albumin to go down.
• Bilirubin - bilirubin is the by-product of the body processing hemoglobin out of the body. This happens normally on a daily basis as the body takes out old, dead red blood cells. It is largely excreted from the body in the bile. Buildup of this compound (which is yellow-orange) causes jaundice or icterus. Increased bili can mean the outflow of bile from the liver is bummed up or it can mean the liver's ability to deal with all of it is overwhelmed (like if the red cells are being damaged too fast).
• GGT (Glutamine amino transferase) - Another enzyme. Very valuable to know in the cat as GGT and ALKP are usually increased together and can help you get a more accurate picture of feline liver function.
• Ammonia - Not routinely done. Ammonia is taken out of circulation and turned into BUN. If blood is shunted around the liver instead of THROUGH the liver (like it's supposed to be) the ammonia levels rise.
• Bile Acids - These are the things that the liver makes and are excreted in the bile. basically they are required to digest and assimilate fats and cholesterol. Sometimes they are used to measure liver dysfunction by measuring them on a fasted sample and one after feeding.

The Other Stuff

• Blood Proteins - Albumin (mentioned above) is made by the liver. It carries all kinds of wonderful things around the body (hormones, drugs, calcium) and when it is low we have to take it seriously. The most common reason for a low albumin is that it is being lost - blood loss or protein loss through the kidneys, gut, or skin (like in burn patients who loose BOAT LOADS of albumin in a hurry). The other population of proteins we look at are the globulins (antibodies). Globulins increase when the immune system is responding to something. Raging high globulins in a cat with fever and fluid in the belly is one hallmark for FIP, for instance.
• Glucose - blood glucose (blood sugar) is quite labile and is tightly controlled by the pancreas (insluin). During periods of stress, the blood sugar increases slightly due to stress hormones like cortisol being produced. Really high levels of blood glucose typically mean diabetes. Really low levels can happen in severe infection, liver failure, small breed puppies (puppy hypoglycemia or small breed dogs), or if there is a tumor in the pancreas secreting EXTRA insulin of if a diabetic is given TOO MUCH insulin.

I'm sure I've forgotten some and the list is already really long. If there is a particular blood chemistry that I've missed and you want to know about, just ask.

AMH