11.4 Point-of-Care and Waived Hematology Tests
Key Takeaways
- CMLA performs FDA-waived/POC hematology: waived hemoglobin, assigned spun microhematocrit, waived ESR, and cartridge devices such as i-STAT-type systems only when that cartridge is waived and on the laboratory menu.
- The heterophile mononucleosis (mono) test is immunology (Chapter 12), not this hematology section.
- Clotted, underfilled, or overfilled EDTA invalidates many hematology results; recollect rather than reporting a printed number from a bad tube.
- Lipemia and hemolysis can bias photometric hemoglobin; mix settled tubes before sampling, and escalate interferents per the IFU and SOP.
- Off-label changes such as extra incubation or dilution of a waived hemoglobin or ESR kit default the method to high complexity, which a CMLA must not independently perform.
CMLA III.6.D is one competency stated as practice: perform point-of-care and waived hematological tests. Terminology, cell functions, instrument QC, and PT/PTT/INR pairing were the earlier lettered areas. This section is the bench: which hematology methods a Certified Medical Laboratory Assistant (CMLA) actually runs, which look-alikes belong in other chapters, and which specimen problems (clotted ethylenediaminetetraacetic acid (EDTA), overfill/underfill, lipemia, hemolysis) make a printed number unreportable.
Quick Answer: Run Food and Drug Administration (FDA)–waived hemoglobin, assigned spun microhematocrit, waived erythrocyte sedimentation rate (ESR), and i-STAT-type cartridges only when that cartridge is waived and on the menu. Follow the instructions for use (IFU). Reject clotted or misfilled EDTA. Watch lipemia and hemolysis on photometric hemoglobin. The mono test is not this section (Chapter 12). Do not modify a waived kit.
What counts as waived hematology on CMLA
Clinical Laboratory Improvement Amendments (CLIA) waived tests are simple methods with insignificant risk of an erroneous result when the IFU is followed (42 CFR 493.15). The original federal waived list includes spun microhematocrit, hemoglobin by copper sulfate, and nonautomated ESR, among other non-hematology tests. FDA has additionally waived specified hemoglobin photometers and some ESR and cartridge systems. Your legal menu is whatever is waived (or otherwise assigned) on the laboratory's CLIA certificate plus the current IFU—not a brand you saw in another clinic.
| Method | CMLA performance | Classic integrity rules |
|---|---|---|
| Waived hemoglobin photometer (cuvette or strip) | Yes, if trained and on the menu | Mix the specimen; correct volume; no clots; no off-label dilution or extra incubation |
| Spun microhematocrit | Yes when the laboratory uses this assigned method | Seal, balance, spin the timed IFU cycle; read the red-cell column, not the buffy coat; no air bubbles |
| Waived ESR kit/device | Yes if that kit is waived and assigned | Level, still, timed; no clots, vibration, or delay beyond IFU |
| Cartridge blood analyzer (i-STAT-type) | Only the cartridges that are FDA-waived and listed on the laboratory menu | Fill the cartridge as IFU shows; no air; no off-menu cartridge |
| Automated CBC counter and smear differential | No independent CMLA performance | Deliver mixed unclotted EDTA to MLT/MLS personnel |
| Heterophile mono test | Not this section | Immunology/serology, Chapter 12 |
Fecal occult blood appears on the federal waived list but is not a hematology cell-count method; skip it here (chemistry/urinalysis-adjacent waived testing is covered elsewhere). Copper-sulfate hemoglobin is historically waived; many sites have replaced it with photometers. If your SOP still uses copper sulfate, follow that IFU exactly—do not invent a specific-gravity cutoff AMT did not print.
i-STAT-type devices are a CMLA trap because the analyzer is not automatically waived. Some cartridges are FDA-waived (for example certain chemistry/hematocrit combinations cleared as waived); other cartridges on the same handle are moderate or high complexity. You perform only the waived cartridge that is on the menu, with that cartridge's IFU. Grabbing a nonwaived hematology or coagulation cartridge because the device is on the counter is practicing beyond the certificate.
How you actually perform the common waived tests
Waived hemoglobin. Confirm patient identification, mix well-mixed capillary or venous whole blood exactly as the IFU specifies, fill the cuvette or strip without bubbles, and read in the labeled time window. Apply the lot calibration (code chip or factory cuvette). Run required QC first (Section 11.2). Capillary first-drop technique follows Chapter 8: wipe the first drop when the IFU/SOP says to, do not milk the finger, and do not use a clotted globule. A hemoglobin photometer result is not a CBC. If the provider ordered a CBC, the waived hemoglobin is not a silent substitute unless the SOP says so.
Spun microhematocrit. Fill the capillary tube from mixed EDTA or from a capillary collection to the IFU mark, seal one end with clay (not your glove), wipe the outside, place the sealed end against the gasket, balance the rotor, close the lid, and spin for the manufacturer's time and speed. Read the packed red-cell column as a percentage of total blood column. Do not include the buffy coat (white cells and platelets) in the hematocrit. Air bubbles, unsealed tubes, an unbalanced head, and reading before the cells are packed invalidate the result. Duplicate tubes are used when the SOP requires them; a large mismatch means recollect or repeat per SOP, not averaging a bubble tube with a good tube.
Waived ESR. Mix the assigned anticoagulated blood, fill to the mark without bubbles, place the tube vertical in a rack that is not bumped, and time the IFU interval. Classic teaching is that delays, clots, vibration, direct sunlight, and a tilted tube falsely change how far red cells fall. Follow the kit; do not move a nonautomated ESR tube halfway through to a busier bench.
Specimen problems: clots, fill, lipemia, hemolysis
Waived methods do not forgive bad specimens. A number on the screen is not automatically reportable.
| Problem | What it does | CMLA action |
|---|---|---|
| Clotted EDTA | Cells and platelets trapped in fibrin; counts and many whole-blood hemoglobin/hematocrit results invalid | Reject and recollect; do not pick out the clot |
| Underfilled EDTA | Excess EDTA shrinks red cells; hematocrit and mean cell volume can fall; morphology distorts | Recollect to the fill line; do not top off from another tube |
| Overfilled EDTA | Additive may be insufficient; microclots form | Recollect; do not shake harder and hope |
| Unmixed / settled | Sampling the plasma layer under-reads hemoglobin/hematocrit; sampling the packed layer over-reads | Invert again per IFU immediately before testing |
| Hemolysis | Free hemoglobin and turbidity; photometric hemoglobin can be biased; many methods flag or invalidate | Do not report against the IFU; recollect a nonhemolyzed specimen if possible |
| Lipemia (and marked icterus) | Turbidity (and pigment) can falsely raise some spectrophotometric hemoglobin readings | Follow IFU interference limits; notify qualified personnel; do not report a known invalid |
| Microhematocrit air bubble or broken seal | Column height is not a true packed-cell fraction | Repeat with a new tube; do not estimate past the bubble |
Hemolysis from a traumatic stick, a squeezed finger, or a shaken tube is a collection error you prevent. If the waived photometer still prints a number, the IFU—not the waiting provider—decides whether that number may leave the bench. Lipemia is milky plasma from high triglycerides (or recent fat load). You may see it in a spun hematocrit tube above the cells. Some hemoglobin methods read the turbidity as extra hemoglobin. Escalate; do not mentally subtract a guess.
Capillary versus venous hemoglobin and hematocrit can differ slightly. Do not relabel a fingerstick as a venous CBC specimen. Warm the site, wipe as required, and fill without air.
What this section is not
- Mono test: heterophile agglutination is immunology (Chapter 12). Mention it only to avoid running it as a hematology CBC substitute.
- High-complexity differential or core-lab CBC: still MLT/MLS work even if you can power the analyzer on.
- Off-label tweaks: extra incubation of a faint hemoglobin cuvette, saline dilution so a thick sample will fill, an expired ESR kit, or an unapproved specimen type defaults the method to high complexity (Chapter 5). A CMLA must not independently perform that high-complexity testing. A control line or a plausible number does not restore waived status.
Scenario
Clinic orders a waived hemoglobin and an ESR. The EDTA tube is underfilled and the plasma layer looks milky. You do not squeeze extra drops from a previously poked finger into the short EDTA tube, and you do not run the lipemic sample because the photometer will print something. You recollect a proper EDTA, mix it, run in-control QC on the hemoglobin photometer, and set up the waived ESR on an unclotted, well-mixed specimen. A nurse hands you an i-STAT cartridge that is not on the waived menu and asks you to incubate a faint cuvette longer. You decline both: off-menu cartridge and extra incubation are not CMLA waived hematology.
Exam traps
- Treating every cartridge on a handheld analyzer as waived.
- Putting the mono test in this section.
- Reporting hemoglobin from clotted, underfilled, hemolyzed, or frankly lipemic specimens against the IFU.
- Including buffy coat in a spun hematocrit, or spinning an unbalanced centrifuge.
- Diluting or over-incubating a waived kit to make it work.
Perform the waived method exactly. Protect the specimen. Leave mono, differentials, and nonwaived cartridges off this bench.
Which set is appropriate CMLA point-of-care and waived hematology work?
How should clotted EDTA, underfill, hemolysis, and lipemia be handled on waived or point-of-care hematology tests?
A nurse asks you to run an i-STAT-type hematology cartridge that is not on the waived menu and to incubate a faint waived hemoglobin cuvette extra time. The correct response is: