What Your Lab Results Actually Mean – Part 1

YOUR HEALTH — Issue No. 7

Most people get their lab results back and do one of two things.

They see everything marked normal and move on without a second thought. Or they see something flagged and spend the next two hours on Google convincing themselves something is seriously wrong.

Neither approach serves you well.

Your lab results tell a story. Understanding the basic chapters of that story — what each test measures, what the numbers mean, and what actually warrants concern — makes you a better participant in your own healthcare.

This issue covers the most common panels your provider orders. Not every value on every test — but the ones that matter most and the questions worth asking.

One thing to know before we start:

Normal ranges vary slightly between labs. What you see on your results may differ slightly from what you read here. Always discuss your specific results with your provider — context matters as much as the number itself.

CBC — Complete Blood Count

The CBC is one of the most commonly ordered blood tests in medicine. It gives your provider a snapshot of three things — your red blood cells, white blood cells, and platelets — and what they can tell us about your overall health.

Hemoglobin and Hematocrit

Hemoglobin is the protein in red blood cells that carries oxygen throughout your body. Hematocrit is the percentage of your blood volume made up of red blood cells. These two values move together and together they tell your provider whether you are anemic.

Normal ranges:

Low hemoglobin/hematocrit — anemia: Anemia means your blood isn't carrying enough oxygen. Symptoms include fatigue, shortness of breath, dizziness, and pale skin. The cause of anemia matters significantly — iron deficiency, B12 deficiency, chronic disease, and bone marrow issues all cause anemia but are treated very differently. When anemia is found your provider will look at additional values to determine the cause.

High hemoglobin/hematocrit: Elevated values can indicate dehydration, lung disease, or in some cases a bone marrow condition called polycythemia vera. Smoking is a common cause of mildly elevated hematocrit. Men on testosterone replacement therapy should have their CBC monitored regularly — testosterone can significantly raise hemoglobin and hematocrit levels over time.

White Blood Cell Count (WBC)

Your white blood cells are your immune system's front line. The WBC measures how many are circulating in your blood.

Normal range: 4,500-11,000 cells/mcL

High WBC: Most commonly caused by infection — your immune system is responding to a bacterial, viral, or other threat. Medications including steroids can also elevate the WBC. Persistently high WBC without an obvious cause warrants further investigation.

Low WBC: Can result from viral infections, certain medications, autoimmune conditions, or in some cases bone marrow problems. A low WBC means your immune defenses are reduced — increasing your vulnerability to infection.

Platelets

Platelets are the cells responsible for clotting. When you cut yourself platelets rush to the site and form a plug to stop bleeding.

Normal range: 150,000-400,000/mcL

Low platelets (thrombocytopenia): Can cause easy bruising, prolonged bleeding, or in severe cases spontaneous bleeding. Causes include medications, viral infections, autoimmune conditions, and liver disease.

High platelets (thrombocytosis): Often a reactive response to infection, inflammation, iron deficiency, or acute bleeding. Persistently elevated platelets can in some cases increase clotting risk and warrants follow up.

CMP — Comprehensive Metabolic Panel

The CMP gives your provider a broad look at how your organs are functioning — specifically your kidneys, liver, and electrolyte balance. It also includes a random glucose.

Kidney Function — BUN, Creatinine, and GFR

BUN (Blood Urea Nitrogen) and creatinine are waste products filtered by your kidneys. When kidneys aren't filtering efficiently these values rise.

The most important kidney number on your CMP is your eGFR — estimated Glomerular Filtration Rate. This number estimates how well your kidneys are filtering your blood and is used to stage kidney function.

GFR Staging — what the numbers mean:

90 and above — Stage 1. Normal or high kidney function. Kidney disease may still be present with other markers such as protein in the urine.

60-89 — Stage 2. Mildly decreased kidney function.

45-59 — Stage 3a. Mildly to moderately decreased.

30-44 — Stage 3b. Moderately to severely decreased.

15-29 — Stage 4. Severely decreased. Preparation for kidney replacement therapy typically begins at this stage.

Below 15 — Stage 5. Kidney failure. Dialysis or transplant required.

An important clinical note: a single low GFR reading does not diagnose chronic kidney disease. Two consecutive GFR readings at the same level — separated by at least 90 days — are required to confirm a CKD diagnosis and stage. A single low reading may reflect temporary dehydration, illness, or medication effect. Always recheck before drawing conclusions.

A GFR of 58 that has been stable for years tells a different story than a GFR of 58 that was 75 six months ago.

Liver Enzymes — ALT and AST

ALT (Alanine Aminotransferase) and AST (Aspartate Aminotransferase) are enzymes found inside liver cells. When liver cells are stressed or damaged they release these enzymes into the bloodstream — raising the values on your CMP.

An important clarification most patients don't hear: elevated liver enzymes do not mean your liver is failing or not functioning. They indicate inflammation or stress to the liver cells. The cause — and the degree of elevation — determines what it means.

Common causes of mildly elevated liver enzymes include fatty liver disease, alcohol use, certain medications, and strenuous exercise. Significantly elevated enzymi require further investigation.

Electrolytes — Sodium, Potassium, CO2

Your CMP includes sodium, potassium, chloride, and bicarbonate (CO2). These electrolytes regulate fluid balance, nerve function, and muscle activity — including your heart.

Sodium — Normal: 136-145 mEq/L

Low sodium (hyponatremia) is one of the most common electrolyte abnormalities seen in clinical practice. It can result from too much fluid in the body diluting the sodium — as seen in heart failure or liver disease — too little sodium intake, or medications that cause the kidneys to retain water inappropriately. Symptoms range from mild (fatigue, nausea, headache) to severe (confusion, seizures) depending on how low the sodium drops and how quickly. Mild chronic hyponatremia is often asymptomatic but still warrants investigation.

High sodium (hypernatremia) is most often related to dehydration.

Potassium — Normal: 3.5-5.0 mEq/L

Both high and low potassium can affect heart rhythm. Diuretics — commonly called fluid or water pills — are among the most common culprits for lowering potassium. This is why your provider checks it regularly if you take one.

Calcium

The CMP also includes calcium. Abnormal calcium levels — both high and low — have important clinical implications and warrant follow up with your provider. We will cover calcium in a future issue.

Random Glucose

The CMP includes a random glucose — a blood sugar reading taken at the time of your draw regardless of when you last ate. Normal fasting glucose is 70-99 mg/dL. A random glucose above 200 mg/dL on two separate occasions meets the diagnostic criteria for diabetes.

A random glucose is not the same as a fasting glucose or an A1c — it is a single snapshot that provides context but requires interpretation based on when you last ate.

Iron and B12 — When Anemia Leads to More Testing

When a CBC comes back showing anemia your provider doesn't stop there. Iron and B12 are the two most common next steps — and understanding why they are ordered helps you follow the clinical reasoning.

Iron Panel

An iron panel is typically ordered when anemia is present and microcytic — meaning red blood cells are smaller than normal. It includes serum iron, ferritin, and TIBC (Total Iron Binding Capacity).

Serum iron measures the actual amount of iron currently circulating in your blood — not your stored iron. It can fluctuate significantly day to day based on recent dietary intake, time of day, and illness. This is why serum iron alone is not a reliable indicator of iron deficiency — it needs to be interpreted alongside ferritin and TIBC together.

Ferritin is the most clinically useful value — it reflects your body's iron stores. Low ferritin confirms iron deficiency even when other iron values appear normal. Normal ferritin ranges vary by lab and gender but values below 12-15 ng/mL are generally considered deficient.

One important caveat: ferritin is also an inflammation marker. In patients with active infection or chronic inflammatory conditions it can appear falsely normal or elevated — even when iron stores are actually low. This is why your provider looks at the full iron panel together, not ferritin alone.

TIBC — Total Iron Binding Capacity measures how much iron your blood could carry if fully loaded. In true iron deficiency TIBC is typically elevated — your body is increasing its capacity to grab more iron because stores are low. In chronic disease anemia TIBC is normal or low — a key distinction that helps differentiate the two.

Iron deficiency is the most common cause of anemia worldwide. In adults over 50 — especially men and postmenopausal women — iron deficiency anemia warrants investigation into the source of iron loss, not just treatment with supplements.

B12 (Cobalamin)

B12 is ordered when anemia is present and macrocytic — meaning red blood cells are larger than normal. B12 is essential for red blood cell production and neurological function.

Normal B12: 200-900 pg/mL. Values below 200 are generally considered deficient. Values in the 200-300 range are borderline and may warrant further evaluation especially if symptoms are present.

Many commonly prescribed medications can deplete B12 over time — including metformin, PPIs, and GLP-1 medications. We cover this further in the Member deep-dive.

If your iron or B12 comes back low — what typically comes next:

Iron deficiency: Oral iron supplementation is the first line treatment in most cases — ferrous sulfate being the most commonly recommended form. It is best absorbed on an empty stomach but can cause GI upset in some patients. IV iron is an option for patients who cannot tolerate oral iron or have absorption issues.

The source of iron loss should always be investigated in adults over 50 — supplementing without finding the cause is treating the symptom, not the problem.

B12 deficiency: Oral B12 supplementation works well for most patients — including many with dietary deficiency or medication-related depletion. High dose oral B12 can overcome absorption limitations in many cases.

B12 injections are reserved for patients with pernicious anemia or severe malabsorption where the gut cannot absorb B12 at all regardless of dose.

A note about lab tests and billing — something most patients never hear:

Your provider cannot simply add a test to your lab order without a qualifying diagnosis. If they do — your insurance may not cover it and you will receive a bill for the full cost.

B12 testing is a good example. It is covered when there is a clinical indication — anemia, neurological symptoms, long-term metformin use, or malabsorption conditions. Without a qualifying diagnosis on the order you may receive an unexpected bill.

This applies to any lab test your provider adds. Before your next blood draw — ask:

"Do I have a qualifying diagnosis for every test on this order? Will my insurance cover all of these?"

The Member deep-dive this week goes deeper on everything flagged above — CBC indices and what they reveal, causes of anemia, abnormal WBC and platelet causes, potassium breakdown including the hemolyzed specimen, CKD progression, and the medications most likely affecting your lab values.

Next week: What Your Lab Results Actually Mean — Part 2. Lipid panel, TSH, A1c, PSA, and Vitamin D — the tests that drive some of the most important conversations in medicine.

Plain Medicine is published for educational purposes only and does not constitute medical advice or establish a patient-provider relationship. Always consult your healthcare provider before making medical decisions.

— Kyle