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Red-cell indices

13 min

  • 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

Read the full reference

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)?

The next section explains it.

Right. The next section explains why.

The next section explains it.

The next section explains it.

Get the idea

Two measurements make three numbers

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 (%)

MCV sorts a red cell as microcytic, normocytic, or macrocytic. MCH tracks cell volume, because a larger red cell usually carries more hemoglobin. MCHC states the hemoglobin concentration inside the average red cell, apart from its size.2

RDW-CV describes the spread

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 alongside older, larger ones. RDW-SD is a separate measurement, reported in femtoliters, and it is read against its own reference interval.1

When the indices don't agree

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 push the MCHC past that ceiling.3 Check the analyzer's flags and the blood film before the indices are released.

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

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 divides hemoglobin by hematocrit, so both inputs need a look before the ratio is trusted.

  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 past that.

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

  3. Check the rule of three: 14.4 × 3 = 43.2, so the expected hematocrit runs about 40.2% to 46.2%. The reported 30% does not fit.

    The rule of three checks hemoglobin against hematocrit outside the MCHC formula, so a mismatch confirms the two don't fit together.

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

    Turbid plasma scatters light at the wavelength the photometric method reads, so it raises the hemoglobin result without a matching change in the red cells themselves.

  5. Keep the CBC pending release, and correct the hemoglobin with a plasma blank or further dilution before the indices go out.

    A repeat on the same turbid plasma reads the same interference again.

Keep the CBC pending release. Correct the turbidity-raised hemoglobin, then recalculate the MCHC, before the indices are reported.

Your turn

Problem 1 of 3

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

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

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

  • 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/µL4.55 × 10⁶/µL2 days ago4.20–5.90 × 10⁶/µL
Hemoglobin18.4 g/dL13.9 g/dL2 days ago14.0–18.0 g/dLHigh
Hematocrit42 %41 %2 days ago42.0–50.0 %
MCV90.9 fL90.1 fL2 days ago80.0–98.0 fL
MCH39.8 pg30.5 pg2 days ago28.0–32.0 pgHigh
MCHC43.8 g/dL33.9 g/dL2 days ago33.0–36.0 g/dLHigh

Specimen: H 3, L 95, I 2. EDTA whole blood; plasma visibly turbid at collection.

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 lipemia index is far above the specimen's usual range, and an MCHC of 43.8 g/dL sits well past the physiologic ceiling. Turbidity from the lipemia raises the photometric hemoglobin reading and, with it, the calculated MCHC.

Hemoglobin, MCH, and MCHC all moved sharply in 2 days with no transfusion or fluid order to explain it. A change like this over 2 days is more often the specimen than the patient.

Review Red-cell indices and RDW-CV

Decision 2 of 3

Is the MCH result reliable as reported?

MCH is calculated from hemoglobin and the RBC count. Whatever affects the hemoglobin reading reaches the MCH as well.

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 sits close to its own baseline, so the same falsely raised hemoglobin that inflates the MCHC inflates the MCH.

The RBC count here sits close to its previous value and within its reference interval. The reading distorted by the turbidity is the hemoglobin.

Review Red-cell indices and RDW-CV

Decision 3 of 3

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

MCV is calculated from the hematocrit and the RBC count. Turbidity affects the photometric hemoglobin reading, and neither of MCV's own inputs is a photometric reading.

MCV = hematocrit × 10 ÷ RBC count. Turbidity raises the photometric hemoglobin reading, and the hematocrit and RBC count are measured a different way.

Every specimen on this analyzer is diluted for the count, including one without turbidity. Dilution is not what separates the affected results from the unaffected ones here.

Review Red-cell indices and RDW-CV

The clue that settles this case is the size of the MCHC, together with what moved and what did not:

  • MCHC of 43.8 g/dL sits well past the physiologic ceiling of about 36 to 38 g/dL.
  • MCH moved the same direction as the hemoglobin that built it.
  • The RBC count and the MCV built from it stayed close to the patient's own baseline from 2 days ago.

The lipemia index and the visibly turbid plasma point to the hemoglobin reading. The indices built from that hemoglobin need the same correction before they are read.

Keep

Sources checked