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Red-cell indices

13 min

Skills you'll build4 skills
  • Calculate MCV using the stated hematocrit and RBC units
  • Calculate MCH using the stated hemoglobin and RBC units
  • Calculate MCHC from hemoglobin and hematocrit
  • Calculate RDW-CV from the standard deviation of red-cell volume and the MCV

Try first

Try first

Hematocrit is 39% and the red blood cell (RBC) count is 4.55 × 10⁶/µL. What is the mean corpuscular volume (MCV)?

Keep going to see the reasoning.

Right. Keep going to follow the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

Calculated red-cell indices

The complete blood count reports the red blood cell (RBC) count, hemoglobin, and hematocrit as separate measurements. Three more values, the red-cell indices, are calculated from them and describe the average red cell.2

MCV (fL) = hematocrit (%) × 10 ÷ RBC count (× 10⁶/µL)

MCH (pg) = hemoglobin (g/dL) × 10 ÷ RBC count (× 10⁶/µL)

MCHC (g/dL) = hemoglobin (g/dL) × 100 ÷ hematocrit (%)

These formulas use a hematocrit measured by the manual spun method. Most automated analyzers measure the MCV from the size of each counted cell and calculate the hematocrit from the MCV and the RBC count.2

MCV classifies red cells as microcytic, normocytic, or macrocytic. MCH usually follows cell volume, because a larger red cell usually contains more hemoglobin. MCHC is the hemoglobin concentration in the average red cell, independent of its size.2

Red-cell distribution width

The indices above describe an average red cell. Red-cell distribution width, reported as a coefficient of variation, describes how much individual cell volumes vary around that average.

RDW-CV (%) = RBC-volume standard deviation (fL) ÷ MCV (fL) × 100

A raised RDW-CV points to a mixed population of cell sizes, such as a newly forming group of smaller cells with older, larger ones. RDW-SD is a separate measurement, reported in femtoliters, and it is interpreted with its own reference interval.1

An MCHC above the physiologic limit

A red cell's hemoglobin concentration has a physiologic ceiling, so an MCHC well above about 36 to 38 g/dL points to a measurement problem.1 Lipemia, in vitro hemolysis, cold agglutinins, and a markedly raised white-cell or platelet count can each raise the measured hemoglobin or lower the counted red cells enough to raise the MCHC above that ceiling.3 Check the analyzer's flags and the blood film before the indices are released.

Follow the bench demonstration

Sources for this step
References
  1. Keohane EM, Preston MM, Mirza KM, Walenga JM, eds. Rodak's Hematology: Clinical Principles and Applications. 7th ed. Elsevier; 2025. Accessed September 26, 2026. https://www.us.elsevierhealth.com/rodaks-hematology-9780323936507.html
  2. Marin MJ, van Wijk XMR, Boothe PD, Harris NS, Winter WE. An introduction to the complete blood count for clinical chemists: red blood cells. J Appl Lab Med. 2024;9(5):1025-1039. doi:10.1093/jalm/jfae031
  3. Gulati G, Uppal G, Gong J. Unreliable automated complete blood count results: causes, recognition, and resolution. Ann Lab Med. 2022;42(5):515-530. doi:10.3343/alm.2022.42.5.515

Watch one

Read each decision and its explanation.

A CBC shows hemoglobin 14.4 g/dL and hematocrit 30%. The collection note says the plasma looked visibly turbid. What do you do with the MCHC before it is released?

  1. Calculate the MCHC: 14.4 × 100 ÷ 30 = 48.0 g/dL.

    MCHC is calculated from hemoglobin and hematocrit, so both are checked before the result is accepted.

  2. Compare it with the physiologic ceiling. MCHC rarely exceeds about 36 to 38 g/dL in a true red-cell population, and 48.0 g/dL is well above that.

    A red cell's hemoglobin concentration has a physiologic ceiling, so a value far above it points to a measurement problem.

  3. Check the rule of three. The hematocrit is usually about 3 times the hemoglobin, within about 3%. Here 14.4 × 3 = 43.2, so the expected hematocrit is about 40.2% to 46.2%. The reported 30% does not fit.

    The rule of three compares hemoglobin with hematocrit independently of the MCHC, and a mismatch confirms that the two do not agree.

  4. Check the collection note. The turbid plasma explains a falsely raised hemoglobin, which raises the calculated MCHC without a true change in the red cells.

    The analyzer measures hemoglobin by the light absorbed by the lysed specimen. Turbid plasma scatters that light and raises the hemoglobin result without a change in the red cells.

Keep the CBC pending release. A repeat on the same turbid plasma has the same interference. Replace the plasma with an equal volume of analyzer diluent, rerun the specimen, and recalculate the MCHC from the corrected hemoglobin.3

Practice this skill

Your turn

Problem 1 of 3 · Hints available

Hematocrit is 36% and the red blood cell (RBC) count is 4.0 × 10⁶/µL. What is the mean corpuscular volume (MCV)?

Correct. MCV (fL) = hematocrit (%) × 10 ÷ RBC count (× 10⁶/µL) = 36 × 10 ÷ 4.0 = 90 fL.

Incorrect. Dividing 36 by 4.0 gives 9 and leaves out the factor of 10 that turns a hematocrit in percent and an RBC count in × 10⁶/µL into femtoliters.

Incorrect. Using a factor of 100, as 36 × 100 ÷ 4.0, gives this value. With hematocrit in percent and the RBC count in × 10⁶/µL, the factor is 10.

Hint
  1. Start from the two measurements the formula uses.
  2. Multiply the hematocrit by 10 before dividing.
  3. Keep the hematocrit as a whole percent.

Review Red-cell indices and RDW-CV

Problem 2 of 3 · Hints available

Hemoglobin is 13.6 g/dL, hematocrit is 42%, and the RBC count is 4.25 × 10⁶/µL. What is the MCH?

Hint
  1. MCH uses the hemoglobin and the RBC count. The hematocrit is not one of its inputs.
  2. Multiply the hemoglobin by 10 before dividing by the RBC count.
Show the answer

32 pg

MCH = 13.6 × 10 ÷ 4.25 = 32.0 pg.

Review Red-cell indices and RDW-CV

Problem 3 of 3 · On your own

The analyzer's RBC-volume standard deviation is 14.0 fL and the MCV is 87.5 fL. What is the RDW-CV?

Show the answer

16 %

RDW-CV = 14.0 ÷ 87.5 × 100 = 16.0%.

Review Red-cell indices and RDW-CV

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • A basic CBC on an adult man (MRN 4471928) is drawn on a medical ward.
  • His CBC 2 days ago was unremarkable: hemoglobin 13.9 g/dL, hematocrit 41%, RBC count 4.55 × 10⁶/µL, MCV 90.1 fL, MCH 30.5 pg, MCHC 33.9 g/dL.
  • The collection note for today's specimen says the plasma looked visibly turbid.
  • No transfusion or fluid order appears in his chart between the two draws.
TestResultPreviousReference intervalFlag
RBC4.62 × 10⁶/µL2 days ago: 4.55 × 10⁶/µL4.55 × 10⁶/µL2 days ago4.20–5.90 × 10⁶/µL4.20–5.90
Hemoglobin18.4 g/dL High2 days ago: 13.9 g/dL13.9 g/dL2 days ago14.0–18.0 g/dL14.0–18.0High
Hematocrit42 %2 days ago: 41 %41 %2 days ago42.0–50.0 %42.0–50.0
MCV90.9 fL2 days ago: 90.1 fL90.1 fL2 days ago80.0–98.0 fL80.0–98.0
MCH39.8 pg High2 days ago: 30.5 pg30.5 pg2 days ago28.0–32.0 pg28.0–32.0High
MCHC43.8 g/dL High2 days ago: 33.9 g/dL33.9 g/dL2 days ago33.0–36.0 g/dL33.0–36.0High

Specimen: EDTA whole blood.

Decision 1 of 3

Which explanation fits these results best?

Spherocytosis raises MCHC only mildly, typically to about 36 to 38 g/dL. It does not explain a value of 43.8 g/dL.

The plasma was visibly turbid, and an MCHC of 43.8 g/dL is well above the physiologic ceiling. Turbidity raises the measured hemoglobin and the calculated MCHC.

Hemoglobin, MCH, and MCHC all changed sharply in 2 days with no transfusion or fluid order to explain it. A change this large in 2 days is more often a specimen problem than a real change.

Review Quantitative hemoglobin: the cyanmethemoglobin method

Decision 2 of 3

Is the MCH result reliable as reported?

MCH is calculated from hemoglobin and the RBC count. Any error in the hemoglobin also affects the MCH.

Divided the hemoglobin by the hematocrit

MCH is hemoglobin per red cell: hemoglobin (g/dL) × 10 ÷ RBC (× 10⁶/µL), so 14.4 × 10 ÷ 4.8 = 30.0 pg. Dividing by the hematocrit calculates a concentration, which is the MCHC.

MCH = hemoglobin × 10 ÷ RBC count. The RBC count is close to the patient's baseline, so the falsely raised hemoglobin raises both the MCHC and the MCH.

The RBC count here is close to its previous value and within its reference interval. The turbidity affects the hemoglobin.

Review Red-cell indices and RDW-CV

Decision 3 of 3

Is the MCV result affected by the turbidity the same way?

The analyzer measures the MCV from the size of each red cell it counts. Turbidity affects the light-based hemoglobin reading, and hemoglobin is not part of the MCV.

The analyzer sizes each red cell as it counts it and reports the average volume as the MCV. Turbidity raises the light-based hemoglobin measurement but does not affect cell sizing, so the MCV stays close to the patient's baseline.

Every specimen on this analyzer is diluted for the count, including one without turbidity. Dilution does not explain why some results are affected and others are not.

Review Red-cell indices and RDW-CV

The MCHC of 43.8 g/dL and the pattern of changed and unchanged results point to the hemoglobin:

  • The MCHC is well above the physiologic ceiling of about 36 to 38 g/dL.
  • The MCH rose with the hemoglobin it is calculated from.
  • The RBC count and the MCV stayed close to the patient's own baseline from 2 days ago.

The visibly turbid plasma explains the falsely raised hemoglobin. The indices calculated from that hemoglobin need the same correction before they are released.

For reference

Sources checked