Clinical pathology

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Author: Mikael Häggström, M.D. [note 1]
Memorization-worthy:[note 2] For the most likely types of cases and/or questions that you may be responsible for, know where to find local policies and procedures, and have a good idea of whom to ask for further advice. Make sure you have access and/or contact details for whenever and wherever you are likely to need them.


For learning hematopathology, focus on the aspects of it that you may be expected to handle rather independently, mainly including peripheral blood smears and general screening of lymph nodes. Otherwise, a hematopathology workup is generally a very complex matter that should be performed by subspecialists thereof. In the unlikely event that you will end up at an institution without an internal arrangement for how to consult a hematopathologist, make such arrangement yourself, since it will save you a lot of time compared to even trying to learn yourself how to perform a modern hematology workup.

Sample tube types

The following is an overview of the main types of sample tube types, organized by order of draw (the recommended sequence by which fluid is drawn) during blood draws:

Tube cap color or type in order of draw Additive Usage and comments
Blood culture bottle Sodium polyanethol sulfonate (anticoagulant) and growth media for microorganisms Usually drawn first for minimal risk of contamination.[1] Two bottles are typically collected in one blood draw; one for aerobic organisms and one for anaerobic organisms.[2]
Light blue Sodium citrate (anticoagulant) Coagulation tests such as prothrombin time (PT) and partial thromboplastin time (PTT) and thrombin time (TT). Tube must be filled 100%.
Plain red No additive Serum: Total complement activity, cryoglobulins
Gold (sometimes red and grey "tiger top"[3]) Clot activator and serum separating gel[4] Serum-separating tube: Tube inversions promote clotting. Most chemistry, endocrine and serology tests, including hepatitis and HIV.
Dark green Sodium heparin (anticoagulant) Chromosome testing, HLA typing, ammonia, lactate
Light green Lithium heparin (anticoagulant) Plasma. Tube inversions prevent clotting
Lavender ("purple") EDTA (chelator / anticoagulant) Whole blood: CBC, ESR, Coombs test, platelet antibodies, flow cytometry, blood levels of tacrolimus and cyclosporin
Pink EDTA (chelator / anticoagulant) Blood typing and cross-matching, direct Coombs test, HIV viral load
Royal blue EDTA (chelator / anticoagulant) Trace elements, heavy metals, most drug levels, toxicology
Tan EDTA (chelator / anticoagulant) Lead
  • Sodium fluoride (glycolysis inhibitor)
  • Potassium oxalate (anticoagulant)[5]
Glucose, lactate[6]
Yellow Acid-citrate-dextrose A (anticoagulant) Tissue typing, DNA studies, HIV cultures
Pearl ("white") Separating gel and (K2)EDTA PCR for adenovirus, toxoplasma and HHV-6

Lab management

Lab management is essentially about handling each of the extremely various lab-related situations that arise, and can generally be achieved by:

  • Common sense
  • Gathering enough information before a decision
  • Identifying what questions needs answering
  • Asking proper expertise and/or looking up relevant information in proper sources (see learning pathology), which may include local protocols as well as policies of accrediting organizations of the department (which are generally more stringent than the national or regional laws).

Test question

Retention time

(You may skip this question if you don't expect to ever be part of laboratory management in the US.)

You work in a pathology department in the United States, which is accredited by the College of American Pathologists (CAP). Your local procedure manual states that non-forensic paraffin-embedded blocks must be retained for at least 10 years before being thrown away. In order to save storage space, one suggestion that gets brought up is to reduce the retention time to 5 years. You look up the issue, and find that federal U.S. law (the Clinical Laboratory Improvement Amendments; CLIA) states that such blocks must be retained for at least 2 years. Is it acceptable to finish the look-up here, and agree to reduce the retention time of non-forensic paraffin-embedded blocks to 5 years in this department?

  • Answer: This pathology department is accredited by CAP, whose requirements commonly exceed those of CLIA, in this case stating at least 10 years for non-forensic paraffin-embedded blocks. Therefore, it is not acceptable to relax minimum retention times without first having had a look at CAP requirements, if the lab is accredited by it (don't assume it isn't without checking). Thus, the answer to this question is: no. Furthermore, state laws need to be considered as well, as they may exceed those of CLIA.

For quick look-up in the future, the following are the most relevant retention times, as given by CLIA[7] as well as by CAP[8] (more comprehensive lists are available in their sources):

Microscopy slides Histology and non-forensic autopsy 10 years[7]
Forensic autopsy Indefinitely[7]
Cytology, fine needle aspiration 10 years[8]
Cytology, apart from fine needle aspiration 5 years[7]
Paraffin-embedded blocks Non-forensic 2[7] or 10 years[8]
Forensic Indefinitely[7]
Requisition forms and test reports Pathology reports 10 years[7]
Other 2 years[7]
Blood bank records Quality control records 5 years[8]
Donor and recipient records 10 years[8]
Records of indefinitely deferred donors Indefinitely[8]
Wet tissues Until report is completed[7] or 2 weeks thereafter[8]
Proficiency testing records and quality management/quality control records (except for blood bank) 2 years[7]
Discontinued procedures 2 years[7]
Blood smears and other body fluid smears, microbiology slides (including Gram stains) 7 days[8]
Flow cytometry plots 10 years[8]

Other clinical pathology articles


  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.
  2. Further information on what is memorization-worthy or not: Learning pathology

Main page


  1. Pagana, KD; Pagana, TJ; Pagana, TN (19 September 2014). Mosby's Diagnostic and Laboratory Test Reference - E-Book . Elsevier Health Sciences. ISBN 978-0-323-22592-2. 
  2. "Chapter 3.4.1: Blood cultures; general detection and interpretation". Clinical Microbiology Procedures Handbook . Wiley. 6 August 2020. ISBN 978-1-55581-881-4. 
  3. . Test Tube Guide and Order of Draw. Guthrie Laboratory Services (June 2019).
  4. . Specimen requirements/containers. Pathology & Laboratory Medicine, UCI School of Medicine.
  5. "Effects of standard anticoagulants and storage procedures on plasma glucose values in seals. ". J Am Vet Med Assoc 201 (1): 145–8. 1992. PMID 1644639. Archived from the original. . 
  6. Amitava Dasgupta; Jorge L. Sepulveda (20 July 2019). Accurate Results in the Clinical Laboratory: A Guide to Error Detection and Correction . Elsevier Science. p. 131. ISBN 978-0-12-813777-2. 
  7. 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 . 42 CFR § 493.1105 - Standard: Retention requirements.. Cornell Law School. [68 FR 3703, Jan. 24, 2003; 68 FR 50723, Aug. 22, 2003]
  8. 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 . CAP Policy Manual - Policy PP. Minimum Period of Retention of Laboratory Records and Materials. Adopted August 1995. Revised September 2020

Image sources