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Globulin, indirect bilirubin and LDL cholesterol

14 min

Skills you'll build

  • Calculate globulin and the albumin/globulin ratio
  • Calculate the indirect bilirubin fraction from total and direct results
  • Calculate non-HDL cholesterol from total and HDL cholesterol
  • Calculate Friedewald LDL cholesterol in mg/dL or mmol/L

Read the full reference

Try first

Try first

A lipid panel reported in SI units shows total cholesterol 5.20 mmol/L, HDL cholesterol 1.30 mmol/L and triglycerides 1.76 mmol/L. What is the Friedewald LDL cholesterol?

Keep going to build the reasoning.

Right. Keep going to follow the reasoning.

Keep going to build the reasoning.

Keep going to build the reasoning.

Get the idea

Use the explanation to check your first decision.

Several routine chemistry results are calculated by subtraction from other results on the same report. Each calculation follows the same rules:

  • use results from one specimen
  • keep them all in the same units
  • label the calculated value apart from the measured ones

Globulin and the A/G ratio

Total protein minus albumin gives the calculated globulin, and albumin divided by that globulin gives the albumin/globulin (A/G) ratio:1

globulin = total protein − albumin

A/G ratio = albumin ÷ globulin

With total protein 6.8 g/dL and albumin 3.9 g/dL, globulin is 2.9 g/dL and the ratio is 3.9 ÷ 2.9 = 1.34. The units cancel, so the ratio has none.

  • Dividing albumin by total protein skips the globulin step and gives a much smaller number.
  • A globulin of zero or below means the component results need checking before any ratio is reported.

Indirect bilirubin

The direct-reacting fraction is measured, and the rest of the total is reported as calculated indirect bilirubin:2

indirect bilirubin = total bilirubin − direct bilirubin

A total of 5.6 mg/dL with a direct of 1.9 mg/dL leaves 3.7 mg/dL indirect. Both results must come from the same draw. A direct result from yesterday's specimen, or one reported in µmol/L, makes the difference meaningless.

Non-HDL and Friedewald LDL cholesterol

Non-HDL cholesterol is all the cholesterol outside HDL, and it works on fasting or nonfasting specimens:3

non-HDL cholesterol = total cholesterol − HDL cholesterol

The Friedewald equation estimates LDL cholesterol by also removing the cholesterol in very-low-density lipoprotein (VLDL), estimated from triglycerides:4

LDL cholesterol = total cholesterol − HDL cholesterol − (triglycerides ÷ 5)

Results inDivide triglycerides byUse the equation only when triglycerides are
mg/dL5Below 400 mg/dL
mmol/L2.2Below 4.5 mmol/L

The original equation was developed on fasting specimens. At 400 mg/dL (4.5 mmol/L) or higher, the VLDL estimate is unreliable, and the laboratory follows its procedure for another method.3,4

Follow the bench demonstration

Sources for this step
References
  1. Bishop ML, Fody EP, Van Siclen C, Mistler JM, Moy M. Clinical Chemistry: Principles, Techniques, and Correlations. 9th ed. Jones & Bartlett Learning; 2023.
  2. Mayo Clinic Laboratories. Bilirubin, Direct, Serum. Accessed August 31, 2026.
  3. Blumenthal RS, Morris PB, Gaudino M, et al. 2026 ACC/AHA/AACVPR/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of dyslipidemia: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2026;153:e1154-e1276. doi:10.1161/CIR.0000000000001423
  4. Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18(6):499-502. doi:10.1093/clinchem/18.6.499

Watch one

Follow each move and the reason beside it.

A fasting lipid panel from one specimen shows total cholesterol 240 mg/dL, HDL cholesterol 38 mg/dL and triglycerides 210 mg/dL. Calculate the Friedewald LDL cholesterol.

  1. Check the triglycerides: 210 mg/dL is below 400 mg/dL, so the equation applies.

    The equation is used only when triglycerides are below 400 mg/dL.

  2. Estimate VLDL cholesterol: 210 ÷ 5 = 42 mg/dL.

    The results are in mg/dL, so the mg/dL divisor is the one that estimates VLDL cholesterol.

  3. Subtract: 240 − 38 − 42 = 160 mg/dL.

    LDL is what remains of the total after the HDL and VLDL shares are removed.

  4. Check: 160 + 38 + 42 = 240 mg/dL.

    The three shares must add back to the total, which catches a slip in the subtraction.

The Friedewald LDL cholesterol is 160 mg/dL.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

Total protein is 7.0 g/dL and albumin is 4.0 g/dL in the same specimen. What is the albumin/globulin ratio, rounded to two decimal places?

Incorrect. 4.0 ÷ 7.0 divides albumin by total protein. First subtract albumin to obtain globulin.

Correct. Globulin is 7.0 − 4.0 = 3.0 g/dL. The ratio is 4.0 ÷ 3.0 = 1.33, with no unit.

Incorrect. 3.0 g/dL is the calculated globulin concentration. Divide albumin by that value to obtain the ratio.

Hint
  1. Globulin is not on the report. Calculate it first.
  2. Globulin is total protein minus albumin.
  3. Then divide albumin by that globulin.

Review Albumin/globulin ratio

Problem 2 of 3 · Hints available

Today's serum specimen has a total bilirubin of 3.6 mg/dL and a direct bilirubin of 0.8 mg/dL. Yesterday's specimen had a direct bilirubin of 1.5 mg/dL. What is today's calculated indirect bilirubin?

This adds the two fractions. The direct result is part of the total, so it is subtracted.

This subtracts yesterday's direct result from today's total. A difference across two draws describes neither specimen.

Subtracted results from different draws or units

Calculated indirect bilirubin is total minus direct from the same specimen in the same units. A difference taken across two draws, or with one result in µmol/L and the other in mg/dL, describes neither specimen and can produce an impossible fraction.

Both results come from today's specimen: 3.6 − 0.8 = 2.8 mg/dL.

Hint
  1. Use results from one draw only.
  2. The indirect fraction is what is left of the total after the direct fraction is taken away.

Review Bilirubin fractionation

Problem 3 of 3 · On your own

A nonfasting lipid panel shows total cholesterol 192 mg/dL, HDL cholesterol 54 mg/dL, LDL cholesterol 118 mg/dL and triglycerides 100 mg/dL. What is the non-HDL cholesterol?

Show the answer

138 mg/dL

Non-HDL cholesterol = 192 − 54 = 138 mg/dL. It needs only the total and HDL cholesterol, whether or not the patient fasted.

Review Friedewald LDL and non-HDL cholesterol

For reference

Sources checked