The Comprehensive Metabolic Panel (CMP) is a series of blood tests for about 20 different chemicals which the body constantly produces. It’s also called a “Chemistry Panel,” and used to be called a “SMA 20”. It includes tests for sodium, potassium, calcium, glucose (sugar), kidney function, liver enzymes, and total proteins. A “Basic Metabolic Panel” (BMP) is the same, without the liver or protein tests.
Patients like it when we order the test and then tell them “everything’s normal.” That’s a lie, of course, because a person can have all sorts of serious illnesses with a normal CMP. Laboratories really like it, because if anything’s abnormal, as it almost always is (see below), the clinician repeats it or orders more tests. The CMP and BMP are automated, and quite cheap for medical practices that have a regular account, but may be expensive when insurances are billed.
Most people have no idea what it means for a test to be “abnormal.” For example, a “normal” potassium level is usually noted to be between 3.5 and 5.2 mEq/L. But, think about it — who says so? Who defines “normal”? Actually, in most cases it’s each individual lab that sets its values, by plotting all its results on a graph, & calling the middle 95% range “normal.”
So by definition, 5% of all results will be “abnormal”, 2.5% of them “low,” and 2.5% “high.” But that doesn’t mean there’s necessarily anything wrong. Since 5% is 1 in 20, statistically, if you do the same test on 20 people, one will be abnormal. That’s also true if you do the same test 20 times on one person. Or — if you do 20 different tests on one person (thus a CMP is likely to always show something abnormal, without necessarily meaning anything).
A friend of mine went to a naturopathic physician, and was told her lipase was low. She was worried. But there are no diseases associated with a low lipase (an enzyme made by the pancreas), & 2.5% of all tests will be low by definition. I just Googled “low lipase” and found a chat group with a bunch of worried participants, which is sad. When an “abnormal” result doesn’t match the overall clinical picture, we properly ignore it. In fact, medical articles used to refer to “within normal limits,’ but now say “within reference range.” Today, no result is “abnormal,” merely “outside reference range.”
Diseases Related to Abnormal Laboratory Tests
That said, there are obviously diseases that can be diagnosed by the laboratory. In terms of the CMP, here is a brief summary of the main tests it includes:
Glucose (sugar): A high glucose is by definition Diabetes; see link for more info. Low glucose (hypoglycemia), if severe, can cause seizures, coma, and death. But it can only occur 1) if a person uses medication to lower blood glucose (like insulin, etc.); 2) from severe alcohol intoxication; or 3) from pancreas tumors & other very rare conditions. So-called “reactive hypoglycemia” in which a person feels jittery & irritable, often after a meal, is not considered an actual disease, and is never life-threatening.
Sodium: A very high or very low sodium can cause fatigue, irritability, confusion, seizures, & even death. High sodium is uncommon, and is due to unusual brain diseases that interfere with thirst. It also occurs when people not only get dehydrated from vomiting, diarrhea, intense sweating, but who also do not have access to water (picture the elderly stuck in a car in a heat wave, or an out-of-shape marathon runner who doesn’t stop to drink [but see next paragraph]). In children, there’s salt poisoning as a form of child abuse.
Low sodium is a little more common, due to certain brain or lung diseases that cause the body to retain water. It can also be due to conditions like heart failure or liver cirrhosis, and to some medications (especially diuretics [“water pills”] for hypertensio; some antidepressants; and ecstasy at raves). Those engaged in long, strenuous exercise who drink too much water can also have their sodium diluted too low.
Potassium: Both very high and very low potassium can cause muscle weakness, even paralysis. More significantly, they can stop the heart. But the word “very” is key. If 3.5 – 5.2 mEq/L is considered “in range,” problems don’t tend to occur until it’s >6.0 heading toward 7.0, or <2.5 (unless it occurs abruptly).
The most common cause of high potassium is laboratory error, if red blood cells aren’t separated out from serum son or completely enough. Certain medications can raise potassium, especially if given in combination, like if somebody taking an ACE-Inhibitor or ARB for hypertension receives a sulfa drug (Septra®, Bactrim®) as antibiotic. Kidney Failure is another cause, also some rare diseases. Low potassium can be due to heavy vomiting, diarrhea, or sweating, some uncommon diseases, and certain medications (especially diuretics [“water pills”] for hypertension).
Calcium: Blood calcium levels are commonly misunderstood. Low calcium in the blood has nothing to do with osteoporosis. And even though consuming too much calcium (dairy products or pills) can cause dangerously high blood calcium levels, and maybe clog coronary arteries in the heart, it doesn’t really protect you bones!
Another problem is that calcium levels can be falsely elevated or decreased depending on the amount of Albumin in the blood (a protein, also measured on a CMP). The usual reference range for Albumin is about 3.5 – 5.2 g/dL. Taking 4.0 as a more-or-less midpoint, for every 1.0 value of Albumin above or below that, correct the Calcium by 0.8. For example:
- If the range for Calcium is given as by the lab as 8.5 – 10.2 mg/dL, and a patient’s is reported as 10.6, that seems “high.”
- But if the Alubmin is 5.0 (i.e. 1.0 greater that our mid-point), subtract 0.8 from the Calcium result, which then comes out “normal” at 9.8.
- Same thing if the calcium is low; correct in the other direction
Lots of clinicians don’t know (or don’t remember) this. So if you’re ever told that your calcium is “low” or “high,” ask what the albumin is. If they seem confused or don’t know, show them this.
Symptoms of Low Calcium depend upon whether the amount drops abruptly, or is chronically low. Rapid onset usually only occurs due to other serious conditions, like after neck surgery, certain types of chemotherapy, acute pancreatitis, or kidney failure. It causes severe muscle pain and spasm all over, possibly seizures and death. I’ve never seen a case in out-patient primary care practice.
Chronic low calcium is usually due to an auto-immune condition hypoparathyroidism, in which parathyroid glands which regulate calcium lose their function (they’re located near, but are completely different from, the thyroid gland). This has virtually no symptoms, but over the years can cause cataracts, osteoporosis (bone loss), parkinsonism, and dementia.
High calcium is a bit more common. It can be caused by kidney failure, certain tumors that secrete a hormone, excessive calcium ingestion (milk, dairy, or calcium pills) or vitamin D ingestion (pills), lithium therapy (for bipolar disorder), Symptoms include fatigue or weakness, depression, constipation, and difficulty concentration. Kidney damage can occur. Severely elevated calcium, which can cause seizures, coma, and death, may be from an undiagnosed Cancer. To identify a tumor as the cause of elevated calcium, the key laboratory test is the Parathyroid Hormone-related protein (PTH-rp) (many clinicians don’t know this; ask for the test if your calcium is truly high)
Proteins: There are two types of protein in serum: albumin and globulins. Some labs report both. Others just report “total protein” and “albumin;” to find the globulins, subtract the albumin level from the total proteins.
High albumin is not a significant. Low albumin is due to malnutrition, or liver failure, since the liver is what makes (synthesizes) it. When a person with liver disease develops low albumin levels, we know the organ is unable to perform any of its tasks well, including detoxifying medications and unwanted substances naturally present in foods (liver failure).
However, low albumin can also be due to a reflex reaction to inflammatory illness, like infection. In this way, the lab test acts similarly to the sedimentation rate or c-reactive protein. In such cases, when the underlying illness resolves, the albumin value rises back to normal.
Elevated globulins occur with any chronic infection or inflammatory disease. I once diagnosed HIV by simply noticing a patient had high globulins, & ordered the test. Patients with high globulins and no obvious cause should also be tested for Hepatitis B and C, and for a variety of unusual diseases, including the blood cancer Multiple Myeloma. These can be suspected by ordering a Serum Protein Electrophoresis (SPEP) and similar test of the urine (UPEP). The tests will identify abnormal types of protein, that clue us in to certain conditions.