What a CBC Test Checks and Factors That Influence It

A Complete Blood Count (CBC) does not directly check liver and kidney function, but it may show indirect signs of problems.

Doctors use other blood tests, like CMP or BMP, to assess how well your liver and kidneys are working.

A CBC can help find anemia, infections, or clotting issues, which may be linked to liver or kidney disease.

Read more: CBC vs CMP: How These Blood Tests Differ?

A CBC does not test for drugs or alcohol, as it only checks blood cells and overall health indicators. Drug tests look for specific substances in blood, urine, or hair, depending on what needs to be detected.

A CBC test won’t show drugs, but if drug use affects your blood health, it might change red or white blood cell counts or platelet levels.

Yes, alcohol can affect a CBC, but don’t mistake it - this test is not used to detect alcohol consumption.

Drinking alcohol before a blood test can cause dehydration, which might lead to higher red blood cell counts and misleading results.

Regular alcohol use can lower white blood cells, weaken the immune system, and affect platelets. That increases the risk of bruising and bleeding. So CBC can show indirect signs of long-term alcohol use.

To get the most accurate results, avoid alcohol for at least 24 hours before your test and stay hydrated with water.

A CBC test won’t tell you if you have skin cancer, but it might show changes if the cancer has spread.

Doctors use biopsies and imaging instead because blood tests aren’t reliable for detecting early-stage skin cancer.

If skin cancer is advanced, blood tests might show higher white blood cell counts or other signs of inflammation or organ stress.

No, a CBC test does not detect pregnancy. 

It measures red blood cells, white blood cells, and platelets, but not pregnancy hormones.

Pregnancy can cause changes in blood cell levels, but to confirm pregnancy, doctors use a blood or urine test for hCG.

A CBC test does not measure blood sugar. It checks blood cell counts, not glucose levels.

If blood sugar is very high or low, a CBC might show indirect changes in blood cells, but it’s not reliable for diagnosis.

For blood sugar levels, doctors order a fasting blood glucose test or an A1C test instead.

Yes, menstruation can slightly affect CBC results, especially if bleeding is heavy.

It may lower hemoglobin and red blood cell counts, making it look like mild anemia.

For the most accurate results, some doctors suggest waiting until after your period to take the test.

A CBC test alone cannot diagnose ovarian cancer, but it might show anemia or an increased white blood cell count.

Doctors use imaging tests, CA-125 blood tests, and biopsies to detect ovarian cancer, as a CBC is not specific enough.