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William Aird Profile picture
@WilliamAird4
Mar 21 • 4 tweets • 2 min read • Read on X
1/4
IGNORE THE MCH!

I don't know about you, but our institution provides the mean corpuscular hemoglobin (MCH) with the CBC.

Not only is it a virtually useless (and redundant) parameter, but it often gets confused with the much more meaningful MCHC. Image
2/4
The MCH is the ave weight of the RBC in Hb (reported in pg). In contrast to the MCHC, it has no place in diagnostic algorithms for anemia.

MCH tracks with the MCV and MCHC (MCH = MCV x MCHC; MCV has the largest effect because % deviation is far greater than with the MCHC). Image
3/4
MCH has been said to be a surrogate marker for MCV. But if we have the MCV in hand, why do we need a surrogate marker?

There are really only two situations in which the MCH yields additional information to the MCV and MCHC: Image
4/4
1. Additive effect low-normal MCV and low-normal MCHC may yield a LOW MCH. So what?

2. The MCH is admittedly a useful surrogate for MCV in situations where the MCV is artifactually altered, for example with prolonged storage of blood.

Bottom line: IGNORE THE MCH!!

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More from @WilliamAird4

William Aird Profile picture
Mar 19
1/4
DEFINITION OF ANEMIA

Yesterday, I posted a poll showing Hb 10.4 and Hct 41 and asked whether or not the patient had anemia.

About 62% of respondents answered YES.

That is the CORRECT answer. Image
2/4
Anemia is best defined by the Hb because patients with anemia have a deficit in oxygen carrying capacity. Hb binds and carries oxygen. The Hct, by contrast, is a function of cell size (MCV) and RBC count. It is impervious to the contents of the RBC. Image
3/4
RBCs could contain Swiss cheese for all the Hct cares. The Hb and Hct happen to correlate with each other only because RBCs package Hb.

This patient has severe iron deficiency (the only other explanation for the discordant Hb/Hct [i.e. low MCHC] would be thal major). Image
Read 4 tweets
William Aird Profile picture
Feb 20
1/12

PERNCIOUS ANEMIA AND ENDOSCOPY

I posted a poll yesterday asking whether you would refer a patient with pernicous anemia (PA) to a gastroenterologist for consideration of upper endoscopy.

Most of you answered YES. Image
2/12

There is no evidence that initial or surveillance endoscopy affects the outcome of patients with PA.

That being said, most GI practice guidelines recommend endoscopy, whereas the sole hematology guideline (BSH) does not.
3/12

All recommendations are consensus based. The justification for endoscopy is that PA is a manifestation of chronic autoimmune gastritis and that the latter is associated with an increased risk of carcinoid tumors and gastric adenocarcinoma. Image
Read 12 tweets
William Aird Profile picture
Feb 19
1/7
CASE

Yesterday, I posted a time series of CBCs and reticulocyte counts and asked a series of questions.

Let's address each question in turn. Image
2/7
Q1. Describe the CBC on 2/11.
A1. Leukocytosis (WBC > 11 x 10^9/L) with normocytic, normochromic anemia (Hb < 12-13 g/dL, MCV 80-100 fL, MCHC 32-36 g/dL), anisocytosis (RDW-SD > 46 fL) and thrombocytosis (PLT > 400 x 10^9/L). Image
3/7
Q2. Why does the MCV increase?
A2. There are only two ways to acutely increase the MCV above normal: reticulocytosis and in vitro artifact. In this case, the retic count is increasing, accounting for the new macrocytosis. Image
Read 7 tweets
William Aird Profile picture
Feb 17
1/5

SVT - TO ANTICOAGULATE OR NOT TO ANTICOAGULATE

I posted a poll asking whether and how you would anticoagulate a patient with superficial vein thrombosis (SVT) of the leg. There was a pretty even split in votes between the 4 options. Image
2/5

Most respondents chose to anticoagulate, though there was no clear consensus on the type/duration of anticoagulation.

In fact, clinical practice guidelines would recommend anticoagulating this patient with either fondaparinux or rivaroxaban for 45 days. Image
3/5

Guideline recommendations for treating patients with SVT of the leg depend on:

1. The proximity of the clot is to the junction with the deep vein.

2. The length of the clot.

3. Whether there are severe symptoms and/or higher than normal risk factors for extension. Image
Read 5 tweets
William Aird Profile picture
Feb 14
1/5

DVT IN BEHCET SYNDROME - TO ANTICOAGULATE OR NOT TO ANTICOAGULATE

I posted a poll yesterday asking whether you'd choose to anticoagulate a 41 yo F with a history of Behcet syndrome (BS) presenting with a DVT. Image
2/5

Most responded YES, which actually reflects current practices (in a 2012 survey 87% of physicians from USA preferred anticoagulation in this setting) but runs counter to some expert opinion and clinical guidelines.
3/5

A. In favor of anticoagulation:

As with any VTE, goal is to prevent clot extension, promote vein recanalization and reduce PTS.

B. In favor of no anticoagulation:

1. Thrombi are formed as a result of inflammation, so therapy should be aimed at the inflammatory axis.
Read 5 tweets
William Aird Profile picture
Jan 26
1/8
DEVELOPMENTAL PLASTICITY AND IRON DEFICIENCY

Developmental plasticity refers to the property (typically adaptive) by which the same genotype produces distinct phenotypes depending on the environmental conditions under which development takes place.
2/8
Developmental plasticity acts by definition over long time-scales, linking conditions present during early stages (development) to phenotypes that may not arise for many years (e.g., late childhood-adulthood).
3/8
A previous study showed that iron deprivation in development (third trimester) in the nonhuman primate, rhesus macaques, was associated in the infant with:

1. Lower mean MCV
2. Lower MCH
3. Lower MCHC
4. Higher RBC count
Read 8 tweets

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