Common Lab Values You Need to Know

Welcome to this video tutorial on lab values. Diagnostic lab tests help determine a patient’s condition, therefore it is important for nurses to be knowledgeable about the different tests and their values in order to make informed clinical decisions. We’re going to look at some common lab values that every nurse needs to be familiar with. Be aware that the normal values, or reference ranges, I’ve listed are just a guide, as the ranges vary from one lab to another.

A complete blood count (CBC) gives an overview of a patient’s general health status by providing information about the cells in a patient’s blood. It includes red blood cells (RBC), white blood cells (WBC), platelets, hemoglobin (Hgb), and hematocrit (Hct).

The normal range of RBCs for males is 4.5-5.5 million/μL, the range for females is 4.0-4.9.

WBCs should range between 4-10.5 thousand/μL.

Platelets range from 140-400 thousand/μL.

The normal range for hemoglobin is 13-17 g/dL for males and 12-15 g/dL for females.

Hematocrit is the ratio of the volume of RBCs to the total volume of blood. In males, it ranges from 41%-50% and females range from 36%-44%.

Another common hematology test is the glycosylated hemoglobin (HgbA1C), which measures the average level of blood glucose over the previous 3 months. It is used to screen for and diagnose diabetes and prediabetes in adults. A nondiabetic person should have a result less than 5.7%. 5.7%-6.4% indicates an increased risk for diabetes. An A1C level of 6.5% or greater is consistent with diabetes.

A lipid profile is used to help predict a patient’s risk of developing heart disease. The total cholesterol measures all of the cholesterol in all the lipoprotein particles and the desirable range is less than 200 mg/dL. The low-density lipoprotein (LDL) cholesterol measures the cholesterol in LDL particles and is called the “bad cholesterol” because it is the main source of cholesterol buildup and blockage in the arteries, contributing to atherosclerosis. LDL should be less than 100 mg/dL. The high-density lipoprotein (HDL) cholesterol measures the cholesterol in HDL particles and is called “good” because it helps remove cholesterol from the arteries. It should be 60 mg/dL and higher to be considered protective against heart disease. You can remember ‘H’ for ‘Happy’ HDL. Triglycerides measures all the triglycerides in all the lipoprotein particles and should be less than 150 mg/dL.

The comprehensive metabolic panel (CMP) is a panel of 14 blood tests that provide a screening of kidney and liver function, diabetic and parathyroid status, and electrolyte and fluid balance. The CMP is an expanded version of the basic metabolic panel (BMP), which does not include liver tests. The individual tests on the CMP include:

Electrolytes in the CMP include sodium, potassium, total CO2 (bicarbonate), and chloride. Electrolyte measurements help investigate conditions that cause electrolyte imbalances such as dehydration, kidney disease, lung diseases, or heart conditions.

Tests specific to the kidney include BUN (blood urea nitrogen) and creatinine.

The BUN test evaluates kidney function. Urea is a waste product formed in the liver when protein is metabolized. When urea is released into the blood, it is carried to the kidneys, where it is filtered out of the blood and released into the urine. If the kidneys are not properly filtering wastes out of the blood, the level of urea in the blood will rise. Normal range for BUN is 8-21 mg/dL.

Creatinine is also an indicator of how well the kidneys are working. Creatinine is a waste product produced by muscles breaking down creatine, which is then filtered from the blood by the kidneys and released in the urine. Normal creatinine blood level is 0.8-1.3 mg/dL.

Tests specific to the liver include ALP, ALT, AST, and bilirubin.

ALP, or alkaline phosphatase, is an enzyme found in the liver and bones and is used to help detect liver disease or bone disorders. Normal range is 25-100 U/L.

ALT, alanine amino transferase, is an enzyme found mostly in liver and kidney cells. When the liver is damaged, ALT is released into the blood, making this blood test useful for early detection of liver damage. The normal range is 7-56 U/L.

AST, aspartate aminotransferase, is an enzyme found in liver, muscle, and other tissues and is usually ordered along with the ALT to detect liver damage. It has a normal range of 10-40 U/L.

Bilirubin is an orange-yellow pigment made during the normal breakdown of red blood cells. It is processed by the liver to allow for elimination from the body. If there is an acceleration of the breakdown of RBCs or the processing and elimination process is affected, there may be an elevated blood level of bilirubin.

There are two forms of bilirubin that can be measured: unconjugated bilirubin and conjugated bilirubin. The total bilirubin includes unconjugated plus conjugated and has a reference range of 0.2-1.2 mg/dL. If the total bilirubin is increased, a direct bilirubin gives an estimate of the amount of conjugated bilirubin present, and ranges from 0.1-0.4 mg/dL. The indirect bilirubin gives the amount of unconjugated bilirubin, which should range from 0.0-1.1 mg/dL.

We’ve now covered all 14 tests on the CMP.

Now let’s look at a brief overview of coagulation studies. You can get a more detailed explanation of these on our videos, ‘Warfarin as an anticoagulant’ and ‘Heparin as an anticoagulant.’

Prothrombin time (PT) measures the number of seconds it takes blood plasma to clot. It evaluates the efficiency of the extrinsic pathway and is used to monitor coumadin therapy. The reference range is 9.5-13.5 seconds.

The INR (International Normalized Ratio) is a calculation based on results of the PT and is used to monitor patients on warfarin/coumadin therapy. The normal range is less than 1.3 and the therapy range is 2-3, with a high INR indicating a higher risk of bleeding, and a low INR suggesting a higher risk of developing a clot. The INR can be used to adjust the patient’s drug dosage to get the PT into the desired range.

The PT is usually performed with a partial thromboplastin time (PTT) and together they assess the amount & function of coagulation factors. PTT is called ‘partial’ because of the absence of tissue factor. The activated partial thromboplastin time (aPTT) tests for the same functions as PTT, but is more sensitive and results in a narrower reference range. It is most commonly used to monitor heparin therapy, with the reference range for PTT at 60-70 seconds and aPTT at 30-40 seconds. The PTT/aPTT evaluates the function of the intrinsic clotting system.

If you like mnemonics, remember PeT PiTT bull for PT evaluating the extrinsic pathway and PTT for the intrinsic pathway. Also, remember the ‘sum of ten’: PT is used to monitor coumadin therapy & the letters add up to 10. PTT is used to monitor heparin therapy & those letters add up to 10 also.

ABG’s (arterial blood gas) measurements are used to evaluate lung function and acid/base balance. An imbalance may occur with heart failure, kidney failure, uncontrolled diabetes, severe infections, and drug overdose.

Arterial blood pH should range between 7.35-7.45. Acidic blood has a lower pH, whereas alkaline blood has a higher pH. PaCO2 is the partial pressure of carbon dioxide and ranges from 35-45 mmHg. When it is out of range, it always indicates a respiratory issue. HCO3 (bicarbonate) ranges from 22-26 mEq/L, and when it is out of range, it always indicates a metabolic issue. PaO2, the partial pressure of oxygen, is 80-100 mmHg, and SaO2 is the oxygen saturation, ranging from 95-100%.

When studying acid-base imbalances, it is helpful to remember ROME – Respiratory Opposite, Metabolic Equal. Both respiratory acidosis and alkalosis have arrows going in the opposite direction for pH and CO2. Metabolic acidosis has both arrows going down, metabolic alkalosis has both arrows going up. For a more detailed explanation, see our video on blood gases.

Thank you for watching this video on lab values!

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