Nursing is all about applying what you know to effectively promote health, prevent illness, and compassionately care for the ill and dying. Although the NCLEX rarely offers up any knowledge-based questions, studying for your boards or nursing school exams invariably means a lot of memorization; after all, you need to learn the knowledge to apply it.
One area where this is especially true is when it comes to lab values. If you know what’s normal, you can easily determine what’s not, so we’ve put together some ways to help memorize some common values.
Complete Blood Count (CBC)
White Blood Count (WBC)
The percentages in WBC that make up the whole count vary a little, but as an aid to memorizing them, stick with just ‘average’ numbers.
Never Let Monkeys Eat Bananas
60, 30, 6, 3, 1
Neutrophils: 60% (range: 55-70% or 2.5-8.0 x10⁹/L SI units)
Lymphocytes 30% (range: 20-40% or 1.0-4.0 x10⁹/L SI units)
Monocytes 6% (range: 2-8% or 0.1-0.7 x10⁹/L SI units)
Eosinophils 3% (range: 1-4% or 0.0-0.5 x10⁹/L SI units)
Basophils 1% (range: 0.5-1% 0.02-0.05 x10⁹/L SI units)
Red Blood Cells (RBC), Hemoglobin and Hematocrit
There are about 5 (million) RBCs (4.2-6.1 million)
Multiply the RBCs by 3 to estimate normal Hemoglobin (Hb) = 15 g/dL or multiply the RBCs by 25 to find the SI units = 125 mmol/L
Hemoglobin for men is 14-18 g/dL (140-180 mmol/L) and women is 12-16 g/dL (120-160 mmol/L)
Multiply the Hb by 3 for the hematocrit = 45% (If you know an easy way to memorize volume fraction, let us know!)
Hematocrit for men is 42-52% (0.42-0.52 volume fraction) and women is 37–47% (0.37-0.47 volume fraction)
A general rule of thumb is that Hematocrit is three times the Hemoglobin (in US values).
Creatinine and BUN
Some people say that Creation took 7 days, which is half (0.5) of 14. 0.5 is the number to remember for Creatinine.
Creatinine for women is 0.5 – 1.1 mg/dL (44-97 mcmol/L) and for men is 0.6-1.2 mg/dL (53-106 mcmol/L).
BUN is 10-20 mg/dL, which is about 20 times greater than creatinine for US values (0.5 x 20 = 10).
To estimate BUN in SI values, creatinine values can be divided by 5 (50/5 = 10 or 100/5 = 20).
Potassium and Magnesium
When it comes to the heart, these two have great influence over each – try to remember the lower range of these values, using the first prime numbers: 1,3 and 5.
Magnesium (Mg): 1.3 mEq/L
Potassium (K): 3.5 mEq/L
35s and 45s
When you are memorizing lab values, you might notice plenty of 35s and 45s. Use this chart to see how they line up.
We have tried to make these work for Canadian lab values as well, but not all of them work. Let us know if you have any mnemonics that are useful for learning lab values in the units common in Canada!