Two blood tests show up at nearly every physical: the complete blood count (CBC) and the metabolic panel, which appears on lab reports as the CMP. Together they cover your blood cells, blood sugar, electrolytes, kidneys and liver. When the results land in your patient portal, they can look like a wall of abbreviations with a few numbers flagged in red.

This guide explains what each part measures, based on the NIH’s MedlinePlus pages, and how to think about a result that falls outside the range.

First, what the reference range means

Every result sits beside a reference range. MedlinePlus explains that these ranges come from testing large groups of healthy people, and that it is common for healthy people to sometimes have results outside the reference range. Labs use different methods, so ranges differ between labs, and you cannot directly compare a result from one lab with another. Using the same lab over time makes trends easier to read.

That is why doctors look at patterns: a value compared with your own past results, alongside your symptoms and medicines. A single flag is a prompt for a question, not a diagnosis.

The complete blood count (CBC)

A CBC counts and measures the cells in your blood:

  • Red blood cells (RBC) carry oxygen from your lungs to the rest of your body.
  • Hemoglobin is the iron-rich protein inside red cells that does the carrying. Low hemoglobin is what most people mean by anemia.
  • Hematocrit is the share of your blood made up of red cells.
  • MCV (mean corpuscular volume) is the average size of your red cells. Small or large cells can point toward different causes of anemia, such as low iron or low vitamin B12.
  • White blood cells (WBC) fight infection. A “CBC with differential” also breaks the total into the five main types.
  • Platelets help your blood clot.

MedlinePlus notes that diet, activity, medicines, menstrual periods and hydration can all affect a CBC, and that an abnormal result does not automatically mean you have a condition that needs treatment.

The metabolic panel (CMP)

A CMP is 14 tests from one tube of blood. A basic metabolic panel (BMP) includes 8 of them and leaves out the liver tests and proteins. Grouped by what they tell you:

  • Glucose is your blood sugar. The CDC lists a fasting result of 99 mg/dL or less as normal, 100 to 125 as prediabetes and 126 or higher as diabetes range. A non-fasting sample reads higher, so it matters whether you ate. See prediabetes and A1c.
  • Electrolytes: sodium, potassium, chloride and bicarbonate help control fluid balance, nerve and muscle function and the acid-base balance of your blood. Diuretics and some blood pressure medicines commonly shift these.
  • Calcium matters for nerves, muscles and the heart, as well as bone.
  • Kidney tests: BUN (blood urea nitrogen) and creatinine are waste products the kidneys clear.
  • Proteins: albumin and total protein. Albumin is the main protein in blood and is made by the liver.
  • Liver tests: ALP, ALT, AST and bilirubin. ALP, ALT and AST are enzymes; bilirubin is a breakdown product of old red cells that the liver clears.

MedlinePlus notes you may be asked to fast for several hours before a CMP. Follow the instructions your doctor’s office gives you, and ask whether you should take your morning medicines.

Where kidney numbers fit in

Most labs also report an estimated glomerular filtration rate, or eGFR, calculated from your creatinine along with age and sex. The NIDDK explains that a GFR of 60 or more is in the normal range, and a GFR below 60 may mean kidney disease. Creatinine comes from muscle, so very low or very high muscle mass, dehydration and some medicines can move it. Our article on reading your kidney lab results walks through eGFR and the urine test that goes with it.

Questions worth asking about your results

  • Is this result new, or has it been like this before?
  • Could a medicine, a recent illness or not fasting explain it?
  • Does it need repeating, and when?
  • What would change in my care if it stays this way?

Call your doctor promptly, rather than waiting for a routine visit, if a result is marked critical or if you are told a value is far out of range and you feel unwell.

At Legacy Medical, Dr. Shtern goes over results with you and explains what they mean for your own health, with an internist’s and a nephrologist’s eye on the kidney numbers in particular. The labs and tests page explains how testing works at the practice. If you would like to meet her, start with a complimentary meet and greet.

This article is general information, not advice for your situation. Members can call the office with questions about their own care.