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Vitamins, trace elements and nutrition markers

15 min

Skills you'll build3 skills
  • Match a vitamin question to a direct, functional, or metabolite measurement
  • Choose metal-free tubes, stoppers, and pipette tips for a trace-element specimen
  • Tell inflammation or protein loss from malnutrition behind a low albumin or prealbumin

At the bench: Assess specimen interference before reporting a chemistry result

Try first

Try first

A clinician orders 1,25-dihydroxyvitamin D to check the vitamin D status of an older woman who rarely goes outdoors. Her calcium and creatinine are within their intervals. Which test assesses her vitamin D status?

Keep going to see the reasoning.

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.

Direct, functional and metabolite assays

  • Direct. The assay measures the vitamin or its active form.
  • Functional. A vitamin-dependent enzyme is assayed with and without added cofactor. A large rise on addition, a high activation coefficient, means the cells were deficient in cofactor. Erythrocyte transketolase for thiamine and glutathione reductase for riboflavin work this way.
  • Metabolite. The assay measures a substrate that builds up when the dependent reaction slows, such as methylmalonic acid for cobalamin.1

For vitamin D the status test is 25-hydroxyvitamin D, with a half-life of 2 to 3 weeks. 1,25-dihydroxyvitamin D has a half-life near 4 hours. PTH, calcium and phosphate keep it near a set point, so it is often normal or high in deficiency.2

Albumin, prealbumin and inflammation

Albumin, prealbumin (transthyretin), transferrin and retinol-binding protein are negative acute-phase proteins. They fall with inflammation regardless of intake.3 Albumin also falls with liver disease, nephrotic syndrome, protein-losing enteropathy, capillary leak and dilution.1 No laboratory value diagnoses malnutrition. It is identified from weight loss, low body mass, muscle loss and reduced intake.4 Report a low protein marker with C-reactive protein, which shows the inflammation that lowers it.3

Trace element contamination

Trace elements are present at such low concentrations that the materials around the specimen can change the result.5,6

  • Stoppers, transfer utensils, ordinary pipette tips, iodine disinfectants and dust add elements, and most contamination raises the result.
  • Puncturing another tube's stopper can carry metal on the needle, so one reference laboratory draws its trace-element tube first. Follow the performing laboratory's own tube, device and draw order. Cap color alone does not certify a tube.
  • Red cells contain about 10 times the plasma zinc and 26 times the plasma manganese. About 1% hemolysis raises zinc by about 5%. Hemolyzed zinc specimens are recollected, because no calculation corrects them.5,7

An unexpected high result is checked against the collection record, and recollected with the specified materials when the procedure calls for it, before it is interpreted as exposure.6

Follow the bench demonstration

Sources for this step
References
  1. Rifai N, Chiu RWK, Young I, Burnham CAD, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier; 2023.
  2. Makris K, Bhattoa HP, Cavalier E, et al. Recommendations on the measurement and the clinical use of vitamin D metabolites and vitamin D binding protein: a position paper from the IFCC Committee on Bone Metabolism. Clin Chim Acta. 2021;517:171-197. doi:10.1016/j.cca.2021.03.002
  3. Evans DC, Corkins MR, Malone A, et al. The use of visceral proteins as nutrition markers: an ASPEN position paper. Nutr Clin Pract. 2021;36(1):22-28. doi:10.1002/ncp.10588
  4. Cederholm T, Jensen GL, Correia MITD, et al. GLIM criteria for the diagnosis of malnutrition: a consensus report from the global clinical nutrition community. Clin Nutr. 2019;38(1):1-9. doi:10.1016/j.clnu.2018.08.002
  5. Versieck J. The collection and preparation of human blood plasma or serum for trace element analysis. J Res Natl Bur Stand (1977). 1986;91(2):87-92. doi:10.6028/jres.091.014
  6. ARUP Laboratories. Trace Elements: Specimen Collection and Transport Guidelines. ARUP-INFO-0016, Rev 0. ARUP Laboratories; September 2019. Accessed September 27, 2026. https://www.aruplab.com/Specimen-Handling/resources/pdf/TraceElements.pdf
  7. Killilea DW, Rohner F, Ghosh S, et al. Identification of a hemolysis threshold that increases plasma and serum zinc concentration. J Nutr. 2017;147(6):1218-1225. doi:10.3945/jn.116.247171

Watch one

Read each decision and its explanation.

An outpatient's serum zinc is 188 µg/dL (reference interval 60 to 120 µg/dL). The requisition records no occupational exposure and no supplements. The collection record shows a gel serum separator tube, drawn third after two other tubes, separated at 1 hour, with a hemolysis index of 5. The performing laboratory's procedure calls for its royal-blue trace-element tube without gel, drawn first. What do you do with the result?

  1. Assess the result. A zinc of 188 µg/dL with no exposure or supplement is unexpected.

    Most contamination raises a trace-element result, so an unexplained high value is investigated first.

  2. Check the tube. A gel serum separator tube does not meet the procedure, and its stopper and gel are not certified for zinc.

    Only a tube and stopper certified for the element keep it free of added metal.

  3. Check the draw order. Two stoppers were punctured before this tube.

    A needle that passes through other stoppers can carry metal into the next tube.

  4. Check for release from red cells. An index of 5 and separation at 1 hour exclude the red cells as a source.

    Red cells contain about 10 times the plasma zinc, so hemolysis or slow separation would also raise it.

  5. Do not report the result as the patient's zinc. Recollect in the trace-element tube, drawn first and handled with certified materials.

    A recollection with the specified materials shows whether the high value is the patient's.

The zinc of 188 µg/dL came from uncertified collection materials. It is not reported as exposure, and the specimen is recollected in the specified trace-element tube drawn first.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

An erythrocyte enzyme is measured with and without added vitamin cofactor. A large activity increase after addition indicates which principle?

Incorrect. Direct measurement quantifies the vitamin or its active form in the specimen. An activation coefficient describes an enzyme's response inside the cell.

Correct. A large increase when cofactor is added means the cell was deficient in the cofactor. Erythrocyte transketolase for thiamine and glutathione reductase for riboflavin work this way.

Incorrect. A metabolite assay quantifies a substrate that accumulates when a vitamin-dependent reaction slows, such as methylmalonic acid. This test measures an enzyme's response to added cofactor.

Hint
  1. The test adds cofactor to an enzyme taken from the patient's cells.
  2. Consider what a large rise in activity shows about the cofactor already in the cells.

Review Three ways to measure a vitamin

Problem 2 of 3 · Hints available

A serum manganese result is unexpectedly high. The collection device, tube, and draw order met the procedure, and the serum was separated on time without hemolysis, then transferred with an ordinary plastic pipette. Which step best explains the result?

Incorrect. Red cells contain far more manganese than plasma, but prompt separation without hemolysis limits their release. The ordinary pipette is the uncontrolled step.

Correct. Ordinary pipette tips and transfer utensils can add trace elements after the draw, and contamination usually raises results. Treat the result as possibly contaminated, and obtain a specimen handled with validated materials before reading it as exposure.

Incorrect. The device and draw order met the procedure, which covers needle-derived metal. The transfer used a pipette not verified as trace-element-free.

Hint
  1. Go through each step from the needle to the analyzer.
  2. Identify the steps the procedure did not cover.

Review Specimen collection and contamination prevention

Problem 3 of 3 · On your own

Three days after abdominal surgery, a man's albumin is 2.4 g/dL, his prealbumin is 9 mg/dL (reference interval 20 to 40 mg/dL) and his C-reactive protein is 180 mg/L. The request reads "nutrition assessment." How do you interpret these results?

Both proteins fall with inflammation regardless of intake, and a C-reactive protein of 180 mg/L shows a strong acute-phase response after surgery. Malnutrition is identified from weight loss, intake and muscle loss.

Read a low albumin or prealbumin as malnutrition

Albumin and prealbumin fall with inflammation, liver disease, renal or gut loss, capillary leak, and dilution, even with adequate intake. Reading a low value as malnutrition labels an acute-phase or loss state as a feeding problem. No laboratory value diagnoses malnutrition, which is judged by weight loss, intake, and muscle loss. A C-reactive protein reported with them detects inflammation.

Albumin and prealbumin are negative acute-phase proteins, and the high C-reactive protein shows the inflammation lowering them. Report them together. Malnutrition is assessed by its clinical criteria.

A repeat will reflect the inflammation as it resolves. A rising prealbumin tracks falling C-reactive protein and cannot confirm or exclude malnutrition.

Review Serum proteins are not nutrition markers

Use it

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

  • A man in a rehabilitation unit has zinc, 25-hydroxyvitamin D, prealbumin and C-reactive protein ordered.
  • The zinc went into the laboratory's royal-blue trace-element tube, drawn first, and it came back hemolyzed after a slow start to the draw.
  • The other tests share one serum separator tube with no hemolysis.
  • Your procedure rejects zinc above a hemolysis index of 50.
TestResultReference intervalFlag
Zinc131 µg/dL High60–120 µg/dL60–120High
25-hydroxyvitamin D14 ng/mL Low20–50 ng/mL20–50Low
Prealbumin11 mg/dL Low20–40 mg/dL20–40Low
C-reactive protein96 mg/L High≤8.0 mg/L≤8.0High

Specimen: Zinc tube H 150, L 10, I 1. Serum separator tube H 8, L 10, I 1. Zinc tube hemolyzed after a slow start to the draw

Decision 1 of 3

What do you do with the zinc?

With a comment, the reported value still includes zinc released from lysed red cells. The index is three times the zinc limit.

No fixed correction gives the patient's true zinc. Hemolyzed zinc specimens are recollected.

Red cells contain about 10 times the plasma zinc, so lysis raises the result. A careful new collection in the specified tube gives a zinc that reflects the patient.

The correct tube prevents contamination from collection materials, but zinc released from lysed red cells raises the result.

Review Specimen integrity and interference

Decision 2 of 3

What do you do with the 25-hydroxyvitamin D of 14 ng/mL?

The serum separator tube is not hemolyzed, and 25-hydroxyvitamin D is the status test. The hemolysis in the zinc tube does not affect it.

1,25-dihydroxyvitamin D is often normal or high in deficiency, because PTH drives its production. It cannot confirm vitamin D status.

Used 1,25-dihydroxyvitamin D as the vitamin D status test

PTH, calcium, and phosphate keep 1,25-dihydroxyvitamin D near a set point, so it can be normal or high in vitamin D deficiency. Vitamin D status is measured as 25-hydroxyvitamin D, which has a half-life of weeks. Measuring 1,25-dihydroxyvitamin D is reserved for the few conditions that change its production, such as kidney failure.

The two tests came from different tubes. The vitamin D specimen is suitable, and waiting delays a result that is ready.

Review Three ways to measure a vitamin

Decision 3 of 3

What do you do with the prealbumin?

Prealbumin falls with inflammation regardless of intake, and the C-reactive protein of 96 mg/L shows inflammation. No laboratory value diagnoses malnutrition.

Read a low albumin or prealbumin as malnutrition

Albumin and prealbumin fall with inflammation, liver disease, renal or gut loss, capillary leak, and dilution, even with adequate intake. Reading a low value as malnutrition labels an acute-phase or loss state as a feeding problem. No laboratory value diagnoses malnutrition, which is judged by weight loss, intake, and muscle loss. A C-reactive protein reported with them detects inflammation.

The specimen is suitable. Reported with the high C-reactive protein, the low prealbumin is interpreted as part of the acute-phase response.

The result is valid for this specimen. The C-reactive protein reported with it gives the reader the context.

Review Serum proteins are not nutrition markers

Each result was handled by the tube it came from:

  • The zinc tube has a hemolysis index three times the zinc limit, and red cells contain much more zinc than plasma, so the zinc is redrawn.
  • The serum separator tube has no hemolysis, so the vitamin D, prealbumin and C-reactive protein are released together.

For reference

Sources checked