Tangent's Challenge

[DrBaboon]

lets try one more: what's the smallest and lightest weight med lab you can come up with. Points for low weight, small size, and most tests performed (both tested for [robustness] and number of single tests that can be done with supplies [longevity] - emphasis on former). Lets aim for a size of fitting in 2 BDU side pockets and under 6 pounds... or a standard M-6 (? - 3 pocket one w/ sholder strap) medic bag as a maximum. Anyone want to try?

A kit fit for a Baboon...

Compur M1000 miniphotometer - hemoglobin 6 3/4" long x 3" wide x 1 1/4" thick ~guestimated at 6-8 ounces empty + 5 AA cells. Miniphotometer Case is more or less rigid -- 8" long x 7 1/2" wide x 1 3/4" thick. About the same weight as the empty miniphotometer, but weight includes 8-10 cuvettes filled with Drabkin's reagent for hemoglobin, associated capillary pipettes, etc.

A jar of urine dipsticks - including: 1) specific gravity, 2) protein, 3) ketone, 4) blood, 5) bilirubin, 6) urobilinogen, 7) nitrite, 8) leukocyte esterace, 9) pH, 10) glucose.

Whole Blood Glucose test strips - one of the brands that can be read visually. I believe some are also individually wrapped. Keep the color chart for reading them. Toss a few in the urine dipstick jar.

Azostix for BUN. Keep the color chart for reading them, and toss some sticks in the urine dipstick jar.

Unheparinized capillary tubes for Whole Blood Clotting time. Either a tube/sleeve/jar of them, or a few tucked into either the miniphotometer case or the urine dipstick jar.

Heparinized capillary tubes for micro Erythrocyte Sedimentation Rate along with a dab of clay to seal one end. Same storage as the unheparinized capillaries above.

Miscellaneous lancettes and supplies, and/or a few tuberculin syringes with 25gauge needles - for blood collection. Tuck them into whatever location seems to work for you - shirt pocket, miniphotometer case or whatever.

Cards and devloper bottle (dropper bottle) for fecal occult blood testing.

A couple Eldon Cards for blood type and Rh. Toss them in the miniphotometer case.

A couple urine pregnancy tests. I believe there are a couple brands that consist of only the strip that's inside the stick. Most people buy one that's inside a plastic stick. Toss the strips in any of the above locations.

Nitrazine Paper - used to help determine if liquid is urine or amniotic fluid. Toss it in whereever you can do so.

Total Tests (if you don't count each test on the urine dipstick individually, and you don't count blood type and Rh as 2 tests):

1) hemoglobin 2) urinalysis 3) blood glucose 4) BUN 5) clotting time 6) ESR 7) occult blood 8) blood type/Rh 9) pregnancy testing 10) Nitrazine Paper.

Size: the case dimensions as above, plus a few things in a pocket, plus the size of a urine dipstick jar. I don't know about fitting cargo pant pockets easily or comfortably - I wouldn't want to walk 20 miles with it rubbing on my leg. Jacket pockets would be OK. Ought to fit into most medical bags with room for other supplies.

Weight: I dunno - haven't packed and weighed it. Guestimate - 4 or 5 pounds - maybe a bit more, maybe a bit less. Pretty sure it would be under 6 pounds.

Short comings: No microscopy, and any of the myriad of things you do with the microscope. There's a long list of tests to get points on that list. No microbiology. AFAIK, neither is going to happen within the 6 pound and size constraints (microscopes, supplies, stains, culture media, incubators, etc.).

Most of the "serology on a card" type tests that I can think of require refigeration, so I did not include them. However, if you wanted to stuff them in someplace, you could claim 1-2-3 or whatever additional tests for the purpose of the challenge - even if they might be ruined.

[tangent]

Excellent post!

buffering and making a shopping list :)

there is that one field microscope - believe under 2 pounds and flat... it was the one used in a portable med lab by one of the relief orgs.

thanks,

-t

ps: how about something on what these tests can tell you and how to interpret the results?

[tangent]

I still don't know med lab stuff well enough to pull together a good list, but some thoughts so far coinside with the list above.

1) whenever possable, use test strips if portability is an issue. The downside is shelf life and cost.

2) the primary piece of basic equipment is a microscope. the most compact one with decent resolution only supports 800x, and for some tests 1000x seems to be the minimum. Is this good enough or what is the smallest one that will do 800x? Other issues are light spectrum, mechanical stage and dark field.

3) secondary piece of equipment is a centrafuge. if very high RPM is not required, a hand crank unit will do and substitutes can be improvised. some tests require very high RPM. best (high RPM unit) I've found is a microcentrifuge using capilary tubes, however, due to volume this won't do for some tests. A different rotor may support larger tubes.

4) reagents can be made up and base components are more stable in their seperate and concentrated form. Downside is that you have to make a fair ammount of the accuracy of the resulting soluton (reagent) is hard to get right. ie: not good for making up for one or a few tests. Also, containers, while potentially lightweight, do take up space.

Things to figure out: what tests are OK at 800x and what need 1000x
what tests require high RPM and what tests are OK at low RPM
what tests are ok w/ capilary tubes and what needs more vollume

think that's the major items... - well, a colorometer...

-t

[DrBaboon]

microscope. the most compact one with decent resolution only supports 800x, and for some tests 1000x seems to be the minimum. Is this good enough or what is the smallest one that will do 800x? Other issues are light spectrum, mechanical stage and dark field.

*snip*

Things to figure out: what tests are OK at 800x and what need 1000x
what tests require high RPM and what tests are OK at low RPM
what tests are ok w/ capilary tubes and what needs more vollume

Darkfield microscopy is useful for some things. I've used a lot of different types (meaning methods - not brands or models) of microscopy at one time or another. I did a lot of phase-contrast on tissue cultures in medical school, and some fluorescence microscopy with labelled "stains." I can't say I've used darkfield microscopy. It's used with intact, unstained cells. You can improvise it if needed. The main purpose I could imagine would be for Treponema pallidum (syphilis). I suspect the yield is quite low for microscopy, compared to serologic testing, so that's probably why we don't use it very often. It's one thing to have primary syphilis and visible lesions, and another thing to show adequacy of treatment, or looking at people with other manifestations of syphilis. You'd pretty much be looking for T. pallidum from (primary) lesions.

The flip side of that becomes whether you'd give someone antibiotics appropriate to primary syphilis based on the lesion even if they had a negative darkfield preparation. I think it's likely you might do so, and regard the darkfield result as either non-diagnostic or a false-negative. OTOH - if you are looking to exclude other types of illness causing a sore -- for example herpes -- you might simply do a Tzanck smear and look for viral inclusions.

I've done Tzanck smears in the office - they are fairly easy as these things go. You need stains appropriate to tissue or blood smears or pap smears. I've used Wrigth-Giemsa stain satisfactorily for them. IOW - if I saw viral inclusions, I wouldn't expend the antibiotics on the assumption of syphilis. I also don't want to give the mistaken impression that clinical history and clinical appearance of the lesions is not important - it's probably at least as important to the decision making.

Anyhow - here are some darkfield links (including how to conjure up a "stop" and use it):

http://micro.magnet.fsu.edu/primer/techniques/darkfieldindex.html

http://www.wsu.edu/~omoto/papers/darkfield.html

http://www.olympusmicro.com/primer/techniques/darkfieldsetup.html

Doing a reality check here... Helpful Terminology: Parfocal and Par-center. What it comes down to is whether the image you see at one magnification ends up being centered on the same point when you switch to a different magnification (parcentered), and whether what was in focus at one magnification is (nearly or approximately/close enough) in focus when you switch to the other magnification.

Inexpensive microscopes are often not either parfocal or parcentered. Beating up a microscope that was once parfocal/parcentered often makes it lose both properties.

I'd insist on one that is both.

The highest power lens should be spring loaded - sooner or later you will run the lens into a slide going the wrong way as you focus. The same goes double for the oil lens. You need to develop habits of approaching the slide or cover slip cautiously while watching from the side, and then moving away from the slide/cover slip while looking through the eye pieces.

Magnification Needs: Well, you can look around and get the general set up at 400 power, but you're not going to see much of diagnostic value. It's really for picking the area of the slide you want to inspect, and approximating your focus. If you're looking at histology, you would also get an overview of how the tissue appears. Basically, you're going to be looking at urine sediment at "high power" so you can estimate how many RBC's and WBC's and epithelial cells or whatever are there per HPF - high power field. That will be 800x.

You're also going to be looking at the hemacytometer most of the time at 800x.

You're probably going to look at gram stains and peripheral blood smears under oil at 1,000x.

You will be surprised how much focus will vary even moving through a smear. That's because the depth of field gets really short at high magnification. Even the thickness of a cell results in slightly different plane of focus.

FWIW - all I have available on my microscope is regular light microscopy, with the addition of my polarizing sunglass lenses when needed (to look at crystals in urine sediment or at joint fluid). Polarizing microscopy will probably be 400x or 800x - depending on what you are seeing. A crystal can be large, and may very well stick out from the slide enough to only focus on a "slice" of it at 800x.

I don't really intend to go after additional capabilities with either a 2nd microscope or accessories. Fluorescence microscopy is very useful clinically for some things, but the reagents are overly specialized and degrade with light exposure, so I don't see it as being helpful. Phase contrast is great for living cells - such as in tissue culture. Not high on the list for austere circumstances, as best as I can tell. Some labs have been known to offer to inspect urine sediment by phase contrast, but the yields are so much higher that it is confusing to shift gears from the regular expectations of how many WBC's or RBC's per HPF is normal/abnormal in conventional light microscopy.

The tests you can do in the capillaries (leaving the blood there) will be hematocrit, possibly whole blood clotting time, and perhaps micro-ESR. If you're using capillaries for other things - you're probably doing so by using the capillary as a measuring device. That means you need to either be able to dislodge the blood into your reaction vessel by aggitating it, or expelling the blood into the reagents.

I don't know if they are still in use, but Wampole used to include tiny rubber bulbs with their "serology on a card" type tests - used to expell a measured amount of serum from the capillary. An example of the test kit that I'm talking about would be a mono-spot (heterophile agglutinin) - correlating it with infectious mononucleosis. I haven't used those kits in 10 years or so.

http://www.wampolelabs.com/clinical/Serology-Agglutination-Test-Menu.asp

Those are the kinds of kits I mean - I didn't find a picture of the individual test and components, so I can't say if it has changed since I used them. I have used the Mono and Rheumatoid factor products.

I don't really see the shelf-life and need for refrigeration of that kind of kit being a help under austere circumstances. I am discussing it for 2 reasons - 1) general information; 2) it *might* be worth getting one kit to have the bulbs available if they still come with it. Of course, that's a little like ordering a pizza so you can have a big sheet of cardboard to stick under your car to see what's leaking... Kind of overkill, and a bit expensive to do it that way. ;)

OTOH - if you have a chance to grab the bulbs when someone is done with the kit, get them. How tiny are they? I don't have one in front of me - but I'd say they are under 1cm - maybe even a few mm in diameter. There's a nipple to go on one end of a capillary, and the other end of the bulb is an open hole to cover with your finger tip before squeezing the bulb to expell the blood.

I think I mentioned previously that Drabkin's hemoglobin recipe uses 5ml reagent and 20microliters whole blood. Or 5 microliters of whole blood in 1.25ml reagent, as is the case with the cuvettes for my photometer. There are 5 microliter capillaries out there - the OEM version called for dropping the capillary into the cuvette with the reagent, and oscillating it to dislodge the blood and mix it with reagent.

You could play with graduating a hematocrit sized capillary or doing volume calculations based on inner diameter. You'd need a way to expell that volume of blood or serum or whatever - hence the tiny bulb.

The other thing to consider would be whether one or 2 fixed volume micropipettes that were the right scale for your assay(s) would be a better choice in some ways. Sure, it's more money, and it's more junk to store, but it's less aggravating, and more repeatable. There are adjustable micropipettes, but I wouldn't use them and keep changing the volume without verifying the volume being dispensed every time I changed the setting on the pipette. That also brings up the question of having pipette tips, and how many trays of them you store, etc. They are not commonly re-used, but I think they could be washed.