1a/ You are on the medicine consult service.

The page comes through “Consult request - hypocalcemia.” https://twitter.com/DxRxEdu/status/1511751200353493003

1b/ How comfortable do you feel with this topic?

2/ I love it when I don’t know something. It is an opportunity to grow. It is more important to know what you don’t know than what you do know. And know that through reflection you can grow.

3/ Do you care about the total serum calcium or ionized (free) Ca?

4/ Ca++ homeostasis is necessary for proper cell function and therefore proper tissue function and therefore life. The cells only see free (ionized) calcium. The total doesn’t matter.

5/ I correct calcium for albumin?

6/ No correction formula highly correlates w/ ionized calcium levels - the Ca that matters - despite what we were taught in training. The bottom line is to obtain ionized calcium if you are concerned about symptomatic hypocalcemia assuming your lab offers it.

7/ What tissues might demonstrate symptoms from acute hypocalcemia?

8/ Note the word “acute” in #7. Chronic hypocalcemia presents differently as the body adapts somewhat to the slow change. Always put a time course on symptoms though know that it won’t be perfect. Just ask @rabihmgeha

9/ The hallmark of low Ca is neuromuscular excitability referred to as tetany. (A single stimulus produces repetitive discharges). The earliest symptoms include perioral and limb paresthesia.

10/ Other symptoms include seizure, hypotension, heart failure, muscle spasms/cramps, papilledema, anxiety, depression, and QTc prolongation though torsades is less common compared to low K and Mg.

11/ Back to the patient. He had just undergone a leg amputation. He had zero symptoms of hypocalcemia. EKG w/ QTc 485. Total serum calcium when corrected for albumin was normal but ionized calcium was quite low.

12/ Do you care about total or ionized?

13/ We need to focus on Rx b/c of the prolonged QTc. Acute + severe AND symptomatic hypocalcemia requires IV Ca. In most instances, you can start oral simultaneously.

14/ It is easy to fix a derangement. Low iron -> give iron. Low potassium -> give potassium. BUT must ask why why why???

15/ I did not feel confident in approaching hypocalcemia but in reading about it quickly recognized the approach is similar to hypercalcemia. Always look for connections. The first step is PTH.

16/ Let’s talk about Ca homeostasis. 3 organs. 3 hormones. 1 Ca++. Say that out loud, no one is judging you. 3 organs. 3 hormones. 1 Ca.

17/ The 3 organs include bone, GI (lumen and liver), and kidney. The hormones act on these three sites. Ca provides appropriate feedback on the kidney and PTH gland through Ca sensing receptors (CaSR).

18/ 1/25-D acts on the GI tract to absorb Ca. But to have 1,25 D need adequate intake, sun, liver function (convert D to 25D), and normal kidney function (converts 25D to 1,25D).

19/ Therefore GI absorption is dependent on the kidney. PTH acts on all 3 sites to increase calcium (osteoclast activation, decreased renal excretion, and increased conversion of 25D to 1,25D and therefore GI absorption).

20/ When creating a DDx you need to think of the base rate.

In vegas, if they asked what caused the hypocalcemia in any patient what would be your response?

21/ ALERT ALERT low calcium is the strongest stimulus for PTH secretion.

22/ What is the cause of hypocalcemia in a patient w/ normal PTH.

23/ #22 highlights when normal is not normal. PTH should be high in low calcium and LOW in hypercalcemia. <3 @rabihmgeha @Sharminzi @ArsalanMedEd

24/ Back to our patient. His PTH was appropriately elevated and vitamin D normal. Then why hypocalcemia??? Twitter said I can't add any more tweets HAHAHAH. Let me know if you want to hear the end of the story <3

25/ Now need to apply the clinical reasoning principle of “sequence of events.” He just had surgery. He did not receive blood products and therefore it was not citrate binding to calcium.

26/ BTW w/ low Ca after citrate usually occurs in patients w/ poor kidney or liver function b/c citrate is quickly metabolized by those organs.

27/ INTERJECTION. Mg is not only potassium’s best friend but also calcium's second cousin. Create a reflex. The patient’s Ca or K is low … What is the Mg? Mg required for PTH to both be secreted and work properly

28/ The patient had respiratory alkalosis. High pH causes ionized calcium to bind to albumin making up for the departed hydrogen ions which leads to low ionized but normal serum calcium in our patient.

29/ Many patients w/ CKD have low calcium (decreased 1-alpha hydroxylation and high phosphate chelating Ca) but don’t have symptoms. Maybe the metabolic acidosis leads to normal ionized Ca despite low total Ca b/c of its makes Ca bind less to albumin.

30/ Hold on!!! We are not done. Why respiratory alkalosis? I will save that for another day. No director reveals all in one thread OR maybe this is just getting too long, LOL.

31/ You are on medicine consult service. The page comes through “Consult request - hypocalcemia.”

How comfortable do you feel with this topic?