"Basic Labs"

[DeadCactus]

What describes you typical testing practice for "basic labs" particularly when the patient is already getting an IV for fluids, meds, or a specific lab test. Examples:

"You're getting an IV, might as well get a CBC and CMP."

"CBC and BMP vs CMP based on clinical situation."

"I carefully deliberate the need for each and every test on every patient."


I think we all support the philosophy of ordering only what is indicated and will make a clear difference in treatment or disposition but in reality likely often sacrifice in the name of decision fatigue or efficiency. I'm curious where people fall on the spectrum.

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[bravotwozero]

usually cbc/bmp for most cases. If it's a gi or CHF issue, will get cmp. If it's a Vag bleeder/miscarriage, will just get a CBC and type and screen.

 

[GeneralVeers]

My discharge papers are included in "basic labs".

 

[Fox800]

Basic labs to me are CBC, BMP, and Mg. I think it’s annoying that Mg isn’t on the BMP. I rarely care about Ca which is included, yet I fairly often replace potassium and would like to know the Mg level. LFTs seem a little more specific and don’t really seem necessary to check a lot of the time so I don’t just routinely order a CMP.

I’m not sure what the point of ordering “basic labs” is though. I’m usually ordering labs for an indication and don’t put a ton of thought into it initially once I see the complaint from an efficiency standpoint. A few examples:

• Chest pain: CBC, BMP, Mg, Troponin (plus/minus ddimer, HCG and UDS)
• Abdominal pain: CBC, BMP, Mg, UA (plus/minus LFTs, lipase and HCG)
• Vaginal bleeding: CBC, HCG (plus/minus T&S if pregnant)
• GI bleeding: CBC, BMP, Mg (plus/minus INR, LFTs, T&S, lactate, ROTEM - not available at my current shop)
• Flank/Back pain (if I even get labs): CBC, BMP, Mg, UA (plus/minus HCG and ESR/CRP in IVDA, sometimes rarely ddimer)
• Headache (only really if I anticipate CTA): CBC, BMP, Mg plus/minus HCG
• AMS: CBC, BMP, Mg, LFTs, lipase, UA, UDS, EtOH (plus/minus troponin, CK, VBG, TSH/fT4, ASA, APAP, ammonia)

Serum mag is not indicative of total body stores. I basically never check it except it's on the DKA order set.

Just give 2 g of magnesium IV if you're giving potassium.

 

[Fox800]

Same for potassium levels, yet we check them. An elevated WBC or lack thereof doesn’t rule in or out an infection. A lot of labs have limitations. I like checking mag levels.

If the serum magnesium level is normal but the K+ is low, would you not give magnesium IV?
I'm not tryna troll. Just curious what you would do.

 

[Fox800]

If the magnesium level is completely normal, and I’m just generally providing basic hypokalemia repletion (hypokalemia of ~2.5-3.5) outside of a scenario such as a toxic overdose or dysrhythmia, then no, I don’t typically also give empiric IV magnesium repletion in addition to potassium. Also from a practicality standpoint you can’t give IV magnesium and potassium at the same time compatibility wise unless separate IVs.

IV mag + PO potassium.

 

[BoardingDoc]

Why bother waiting 30 minutes for the IV magnesium if you are just giving PO potassium. PO and go. Discharge. These are mostly just style things.

Should always give Mg PO if you're doing it for repletion unless the patient is symptomatic. IV Mg is poorly absorbed. Even when doing it PO, you should be ordering it as MgCl and not as Mg oxide if possible as the former is slow absorbing and subsequently is also absorbed to a greater degree.

IV mag is for asthma, preeclampsia, severe HypoMg with sx etc etc.

 

[WilcoWorld]

Of course basic labs include a blood count, otherwise it's right there in the names.

Basic metabolic panel = BMP
Comprehensive [sic] metabolic panel = CMP

 

[Fox800]

Should always give Mg PO if you're doing it for repletion unless the patient is symptomatic. IV Mg is poorly absorbed. Even when doing it PO, you should be ordering it as MgCl and not as Mg oxide if possible as the former is slow absorbing and subsequently is also absorbed to a greater degree.

IV mag is for asthma, preeclampsia, severe HypoMg with sx etc etc.

I love that we're all arguing like a bunch of internists in here. Makes me strangely happy.
I think you just changed my practice, FWIW.
Have never ordered PO magnesium chloride, I'll give it a go next time.

 

[thegenius]

If the serum magnesium level is normal but the K+ is low, would you not give magnesium IV?
I'm not tryna troll. Just curious what you would do.

I don't

 

[turkeyjerky]

I love that we're all arguing like a bunch of internists in here. Makes me strangely happy.
I think you just changed my practice, FWIW.
Have never ordered PO magnesium chloride, I'll give it a go next time.

I happened to do a deep dive on mag replacement a few months ago (well, if you consider reading an online article about it 'deep', but you know). A local NP had referred her patient in for "Needs IV Mag" for like the 4th time in a month. Evidently the patient kept having mag levels in the .6-1.2 range. They'd get sent it, get a couple of grams of IV mag and then discharged +/- continued PO replacement.

It turns out we're all doing mag replacement wrong.

--IV is poorly performed, because most of it just gets excreted by the kidneys. If you are going to give it IV, then it should be via longer infusion (the typical 2 g over 2 hours) in contrast to other indications for IV mag (afib, asthma, etc) where you should be giving it rapidly.
--PO replacement is also poorly absorbed (diarrhea), and takes a long time. 1-2 tabs of mag oxide for a few days doesn't cut it. Better is MgCl, and about 2 tabs QID. Long duration of therapy often required (because it takes long time to equilibrate between serum and intracellular stores)

 

[Groove]

Well, how about that. You learn something new every day. Thanks for the Mg PO tip, I'll order MgCL next time.

I'm another one that does order Mg more frequently than my partners for many of the reasons above. Apparently, I've been repleting it incorrectly.

I also have a weird habit of ordering Direct Bili with my CMP. It's beyond frustrating to me that they don't include a direct bilirubin. I guess I could just order a BMP and LFT panel but I don't seem to ever do that.

To the OP, it really just depends on why you're ordering the tests. I don't order labs on plenty of people, nor do I need any to disposition them. However, with the majority of chief complaints, you can generally rationalize the need for a chemistry at the very least in my experience. Especially when you are in a pt population like mine where everyone seems to be in heart failure and on dialysis.

 

[BoardingDoc]

We are now in the electrolyte weeds. Is this the Nephro forum?

You contradict yourself somewhat though in saying that you should always give PO mag if for repletion without symptoms, but IV mag for severe hypomagnesemia with symptoms. If IV mag is poorly absorbed compared to PO why give it IV if they have symptoms? I’m skeptical too that it’s easy to correlate symptoms with mag levels.

So @turkeyjerky touched on the answer above. To get further into the weeds on this one, Mg is slowly absorbed, regardless of whether it is IV or PO. Patients who are symptomatic from HypoMg usually have critically low Mg levels and are at risk of seizures or torsades and generally need to be admitted and monitored. Because of said risks, they also generally need to be NPO. Hence the IV Mg.

If they're actively seizing, you're giving them the 2g push of Mg like you would with preeclampsia. The point is to get a bunch of Mg in their system and hope that enough absorbs. That said, much of it won't absorb and you likely need to treat with standard modalities such as benzos. Same for torsades. Give them a hit of Mg, but you're not foregoing the electricity. After you give the IV push, you keep them on a mag drip, but it is SLOW. Like, infusing it over a full day or more slow. Otherwise, they're just going to piss out all the Mg you're giving them.

The same is true for Mg oxide (except they're mostly going to crap it out instead of pissing it out as Mg Oxide works as an osmotic laxative).

MgCl is a slow release preparation. This has the benefit of A: not giving the patient the runs, and B: accomplishing the same thing that the slow trickle infusion of Mg IV does, but now the patient can go home instead of hooking them up to an IV for a full day.

TL;DR: Mg is absorbed very slowly, regardless of whether it is PO or IV. There's no point in IV Mg for repletion unless the patient is critically ill or has a level so low that you expect them to seize/have torsades and they're being admitted/monitored/NPO.

 

[Brigade4Radiant]

Just send patients home with mag chloride

 

[pkwraith]

I had a (incrediably smart) ICU Attending one time, and magnesium was one of his biggest obsessions. We would be giving like 8 -10 grams of IV magnesium replinishment to patients with essentially normal range magnesium, and pharmacy would be also like "WTF? Oh it's Dr X".

BMP is my standard. I just go with BMP+LFT instead of a CMP when I am interested in the liver. But I will just get one lab on someone if they're young and they're here for a specific reason.