Do I need to memorize common lab values?

Memorizing common lab values used to be a toughie, but thanks to the modern Electronic Health Record (EHR) and full computer access, nurses don’t need to memorize most lab values.

The other caveat to lab values is that each institution has its own set of normal value ranges. One “norm” may not be the same as another neighboring institution or facility. The difference is usually ± 1-3 percent.

As a nurse, it’s normally your job to notice and address extreme values that do not coincide with your patient assessment, but always keep them in the context of the patient.

And to make matters even more complicated, some values will be read and displayed using different methods of measurement. Instead of mmHg, they could use cm of H2O. Just something to pay attention to.

Outside of memorizing the values outright, here are a couple helpful tips to keep in mind:

Hemoglobin and Hematocrit (H and H)

• General rule of thumb is a 1:3 ratio
• Hematocrit should be approximately 3X the Hemoglobin
• Norm ~ Hgb 10 / Hct 30 (minimum values)
• Also Hgb 13 / Hct 40 accepted

BUN and Creatinine (Cr)

• General rule of thumb is a 1:20 ratio
• BUN should be approximately 20x the Creatinine
• Norm ~ BUN 20 / Cr 1.0

Sodium (Na)

• As a critical care nurse, I memorized the last two digits
• The last two digits were the same for a normal pH level
• (normal pH ~ 7.35 — 7.45)
• Normal Na ~ 135-145

Potassium (K) and Magnesium (Mg)

• These two electrolytes have a great influence over each other
• Significant cardiac involvement
• Memorize and use them together as a pair — always
• K ~ 3.5-5.2
• I started by memorizing 5.0 as a limit
• Mg ~ 1.8-3.0
• I started by memorizing 2.5 as acceptable
• 2.5 happens to be half of 5.0
• How convenient, since K and Mg are treated as a pair!

Phosphorus (Phos) and Calcium (Ca)

• These two electrolytes have an inverse relationship. As one increases, the other decreases, and vice-versa
• Phos sometimes gets treated as a trio with K and Mg (depends on the physician ordering or treating abnormal levels)
• Normal Phos ~ 2.4-5.1
• You could start by using 2.5 as minimum reference (since you already are memorizing that number for Mg)
• Normal Ca ~ 8.5
• Sorry, no cool suggestions for this one. Just simple memorization!

Whatever you do, don’t treat ANY lab value as if it lived in a vacuum. Apply what you see in the context of the patient. Above all, always verify.

What are some of your memorization tips and tricks?