HesapHanem

Estimated Plasma Volume Calculator

Estimate plasma volume and congestion status from body weight, hematocrit and hemoglobin.

How it is calculated

Two estimates are produced. First the Kaplan-Hakim plasma volume: total blood volume is a + 41 × weight (kg) mL, where a = 1,530 for men and 864 for women, and plasma is the part that is not red cells, plasma = (1 − hematocrit ÷ 100) × blood volume. Second the Duarte plasma volume status, ePVS = 100 × (1 − hematocrit ÷ 100) ÷ hemoglobin, in mL per g/dL of haemoglobin (a ratio, not a percentage). The tool reads the ePVS as below 4.0 low, 4.0 to 5.5 usual, above 5.5 suggesting expansion (congestion), and the interpretation text appears in the page language. Weight is in kg (2 to 650), hematocrit in percent (5 up to just under 100) and haemoglobin in g/dL (2 to 30); anything outside these ranges shows no result. The sex field selects the constant; a missing or unrecognised value is treated as male. Educational use, not medical advice.

Worked example

A woman weighs 62 kg with a hematocrit of 38% and haemoglobin of 12.5 g/dL. Blood volume = 864 + 41 × 62 = 3,406 mL. Red cells take 38%, so the plasma fraction is 1 − 0.38 = 0.62. Plasma volume = 0.62 × 3,406 = 2,112 mL, which is 2.11 L. ePVS = 100 × 0.62 ÷ 12.5 = 4.96 mL/g, inside the 4.0 to 5.5 band the tool calls the usual range.

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Common mistakes

  • Entering hematocrit as a fraction (0.38) instead of a percentage (38). Values below 5 are rejected, so you get no result rather than a wrong one.
  • Entering haemoglobin in g/L (125) instead of g/dL (12.5). Anything above 30 is rejected, so the tool shows no result.
  • Choosing the wrong sex, or leaving it unset: the unset value counts as male, and the constant differs by 666 mL of estimated blood volume.
  • Comparing the ePVS figure with the plasma-volume litres: they measure different things, one a volume and the other a ratio.
  • Calling a single ePVS a diagnosis of congestion or dehydration; it is a screening number that depends on the lab values on that day.

Sources

About this calculator

The Kaplan-Hakim formula estimates plasma volume from routine blood values: Plasma volume (mL) = (1 − hematocrit) × [a + (b × weight in kg)], with sex-specific constants. From that estimate, estimated Plasma Volume Status (ePVS) is the Duarte value, 100 × (1 − hematocrit) ÷ hemoglobin, expressed in mL/g. It is not a percentage against an “ideal” volume; instead it is read in bands (below 4, 4 to 5.5, above 5.5 mL/g) that indicate whether plasma volume looks low, usual or high, as a pointer to volume depletion or congestion.

Cardiologists use ePVS specifically in heart failure management, where it has emerged as a useful, calculation-only marker of congestion — since it's derived entirely from a standard complete blood count (hematocrit, hemoglobin) and body weight, it doesn't require the invasive or expensive testing that direct plasma volume measurement would, making it practical to track at every clinic visit or hospital admission.

Body weight, hematocrit, hemoglobin and sex give the estimated plasma volume, the estimated blood volume and the ePVS value with its band.

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